RPM theshold discussion

[Larry Gibson]

DrB

Here's the thread. Please address the examples and points I gave you to consider in your thread, answer my questions and give the parameters of that "test" you mentioned to prove or disprove the RPM threshold.

Larry Gibson

[Char-Gar]

This ought to be interesting.

[Larry Gibson]

This ought to be interesting.

That it should be unless all they want to do is argue it is a "limit" or request a hard and fast RPM figure to say it is a "limit'..Do I have to mention the RPM threshold is not a "limit" BTW?:wink:

Larry Gibson

[Wayne Smith]

Larry, how many times have you mentioned that already? I think I can remember at least six!

[Larry Gibson]

Larry, how many times have you mentioned that already? I think I can remember at least six!

Umteen bajillion probably.........:roll:

Larry Gibson

[303Guy]

OK. So for me, I want to know what a reasonable velocity is going to be for my 303 Brit. A threshold is going to mean a zone into which things start to get difficult. If you tell me the thrshold is 2200fps then I would expect to not have spin rate issues below that velocity but above that I do need to take it into account. That means that 2200 fps isn't a threashold but rather, from about 2200 fps to about 2400 fps is. The threashold is going to be a 'grey area'. It could also mean that above that threshold things could get better because one set of influencing factors give way to another. Maybe those would include boolit distortion as it exits the muzzle of after it has left the muzzle. Maybe even friction erosion of the boolit in flight plays a role but that's independant of spin rate.

[geargnasher]

Larry, how about a cut'n'paste of your condensed thesis, say, in the OP, so the rest of the world that hasn't been reading about this for years knows what you're talking about?

Gear

[Larry Gibson]

303 guy

It is not a "grey area". However, I can not tell you what it will be, your rifle with the bullet and componants you use will. That is just as i can not tell you the exact velocity your rifle will be the most accurate at. Sounds like a non answer but it is not. Let me explain; assuming your 303 Brit has a 10" twist and you use a 311291 or some similar cast bullet, you cast them of WWs and WQ, they are sized correctly, you use an adequate lube and a GC, the cases are properly fire formed to the chamber and you are using a medium burning powder such as 4895. With such your best accuracy will be in the 120,000 - 140,000 RPM or 1650 fps to 1950 fps. If the bullet fits really well and you use a slower burning powder such a AA4350 or one similar that give consistent ignition then you may push it maintaining that best accuracy up through 2100 fps/ 151,000 RPM. However, if you use one of your custom solid type cast bullets that leave little to no room for unwanted obturation, setback, sloughing, etc. during accelleration with a slow burning powder then you may very well get equal accuracy upwards of 2300 - 2400 fps or 170,000 RPM give or take.

Somewhere in there at a certain point (RPM) with either bullet and componants the centrifugal force will act upon any imbalance in that bullet and the bullet will begin to helically spiral losing accuracy in a non linear fashion as range increases. The rifle and the load/componants will tell you when it has reached the RPM threshold because you will begin to get those uncalled pesky little flyers. Exactly where that will be (either in velocity or RPM) I can not tell you. I will tell you though that if you are using a regular cast bullet of proper alloy that is well cast to get or maintain "best" accuracy at higher than 1950 fps/140,000 RPM will take attention to detail on your part in the casting, sizing, loading process. If i recall correctly you are getting some decent accuracy out of the 303 at higher than 1950 fps. I also recall that you do take care and pay attention to detail which is why you are successful in pushing the RPM threshold higher with your loads and componants.

Larry Gibson

[Larry Gibson]

Gear

Have you any idea how many times I have posted all that in the last 8 years on this forum? Here's what I posted on DrB's thread;

I have described the RPM threshold many times. I have already posted the basis of it in this thread but will post it here again;

“The bullet is unbalanced or becomes unbalance due to obturation in the bore during acceleration. The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around its geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release. After exiting the muzzle, the geometric center will begin to revolve about the center of mass and it will depart at an angle to the bore (line of departure). At 54,000 RPM to 250,000 RPM, depending on velocity and twist, the centrifugal force can be tremendous. It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.”

Generally this means that with a regular cast bullet common today, cast of an alloy with a BHN of 16 – 22, GC’d properly, with a good lube, sized correctly, driven with a medium burning powder in a case with a medium bore ratio capacity will give its best accuracy up through 120,000 – 140,000 RPM. Where, exactly, in there depends on the combination of variables and conditions. Above that the RPM threshold is when the centrifugal force becomes strong enough that the bullet begins to follow a helical path outwardly from the line of departure or intended path. The “diameter of the path” is dependant on the centrifugal force (the higher the RPM over the threshold the higher the centrifugal force and the larger the diameter of the helical spiral will be) and the range at which measured. It is not a constant diameter but increases as the range increases. This is the why/where the non linear expansion of the groups comes from and why it is more pronounced at longer ranges past 100 yards.

The RPM threshold may be lowered in a given cartridge with a given bullet simply by using a faster burning powder. You may very well get 1 ½ moa accuracy in an ’06 with a 10" twist using a 311291 cast bullet with 4895 powder at 1900 fps. But if you switch to Unique powder will you get 1 ½ moa at 1900 fps? No, you won’t because the acceleration (the time/pressure curve) is much quicker with Unique and the bullet sustains more obturation, setback, sloughing, etc. during this acceleration. This creates a much more unbalanced bullet of which the centrifugal force will act on sooner and to a greater degree to begin that helical spiral. Conversely the RPM threshold can be raised by using a slower burning powder than 4895 and we can get 1 ½ moa upwards of 2000+ fps. That of course has an increased RPM. what we have done there is to lengthen the time/pressure curve to lesson the obturation, setback, sloughing , etc. and thus having a less unbalanced bullet on exit from the barrel. Thus there are many variables and conditions that affect exactly at what RPM the threshold occurs so we can not give an exact RPM that it will occur at.

The point being is that at some level of RPM the helical spiral will begin if the bullets center of spin does not coincide with the center of gravity and center of form. This is the RPM point at which threshold for that particular cartridge and components will begin. Most every ballistics book/manual has a description of the helical spiral. I use that ballistic definition. The “forward progress per revolution” or the diameter of the helical spiral is dependant on the degree of unbalance and the amount of centrifugal force as already explained. By “per revolution” if you are thinking of the revolution of the bullet (spin) then you misunderstand. The revolution of the helical spiral around the line of departure (intended flight path) is not the same as the revolutions (spin rate) of the bullet to maintain point on stability. The bullets may very well maintain complete rotational stability while following the helical spiral caused by increased centrifugal force acting upon the unbalanced bullet.

If, perhaps, you’re not still understanding my explanation of "helical spiral" then consider the simple example of a balanced tire vs an unbalanced tire as speed/RPM is increased. What occurs to the balanced vs unbalanced tire is the same as what happens to the cast bullet (actually any unbalanced bullet but it's more pronounced and obvious with cast bullets). Consider that you are looking a a cross section of the bullet as you consider the tire and are looking down along the line of departure.

Larry Gibson

[btroj]

So if I understand this correctly a bullet that is cast with no voids from a very round mould, size correctly, and well balanced will have a better potential to be shot at high velocity with good accuracy than one that is somewhat our of round or sized such that it becomes slightly unbalanced.
Interesting concept Larry. I do like the explanation of why a bullet can be accurate at a certain velocity with one powder yet with a different powder accuracy at that velocity may be very poor.
I rarely shoot cast over 1800 fps but will need to look at RPM as a variable along with pressure, velocity, and others.

Interesting.

Brad

[geargnasher]

Larry, I know that every time this comes up it seems that you get swarmed with a bunch of people simply hell-bent to discredit you, and a couple interested in polite conversation. I'm not out to put you on the defensive, so please don't get that way, but the more I shoot cast the less I subscribe to your theory. I observe similar trends with RPM and accuracy limitations, but I simply don't believe that RPM has much to do with it, both because I've noticed corollary trends involving other factors, the physics doesn't make sense, and because I've noticed some things that just don't support the boolit behavior you postulate is responsible for large groups exceeding the particular "RPM Threshold" of the load.

First, and someone brought this up on DrB's Lotak thread, why is it that even an average reloader can take a boolit, say the classic 311291 in a .30-06, find that cast from Lyman #2 and checked it can be fired with 1.5 moa accuracy up to about 1800 fps from a ten-twist bolt-action sporter, but if the same boolit, sans check, is sized to .301" and half-arsed patched with some cheap notebook paper it can be fired with the same accuracy at, say, 2500 fps with a powder appropriate for the velocity/pressure/boolit weight? This happens predictably, often with no special loading techniques or case prep, and often with bore-rider designs where the nose portion, the portion most often blamed for HV unbalance is left bare and un-supported by the patch! WHY? A patch supporting the driving bands at the land contact points doesn't explain much, because that part is supported by the barrel anyway, right? The paper doesn't have any power to protect the nose from slump, the lube grooves from collapsing (boolit accordion), or anything else related to balance that I can think of. If you twist a tail and clip it long enough to make a wad behind the base accuracy is improved, I think mainly due to acting as a wad and sabot to the boolit's base and making it exit the muzzle straight. The way the patch seems to work is by literally acting as a flexible gasket which prevents gas-cutting and leading to a degree large enough to allow the boolit to be fired 25-30% faster with the same accuracy. So I don't think RPM is ultimately what makes a PP boolit reach an accuracy limit. In many cases the peak pressure of the load is the limiting factor to velocity, not the projectile, and accuracy can be maintained in many cases up to that pressure limit.

Second, and I don't think this has ever occured to anyone, if lack of balance from some boolit defect (incited at launch or when cast or loaded) is truly making a boolit follow a helical path of any significance (significant being enough to cause your group dispersion observations partly responsible for your theory's existence), then the groups would show a certain trend to being rings on the target. They would be doughnuts. I do not observe this in my HV groups when they start to fall apart, have you?

Last, following my second query, are some thoughts and questions based on with my observations of boolits being actually fired. I've had several opportunities recently to observe long-range shooting of cast boolits that were, in one case at least, well above the RPM threshold for the gun/boolit, and were indeed making fairly large groups at long range. The interesting thing for me, sitting directly behind and inches above the shooter with a 50-power spotting scope, was I could call a 300 yard shot right out of the muzzle after I'd had a chance to note trends of flight and get used to seeing the boolit in the air. If it were going high and right, it was doing so right out of the muzzle, NOT smacking the paper high and right just because it encountered the target at that point in it's corkscrew path. I never saw any significant "helix" pattern to the flight, and I could clearly see it's path, arc, turbulence of the air around it, and impact with the target. Out further, at 400 and 500 yards it's harder to see the whole path of the boolit, and at my local range there is a valley with some wind currents between 300 and 400 yard berms, but I could clearly see the boolit ride the wind currents. They tended to zig and zag, really neat to watch the boolit's flight path as it encountered temperature layers of the air, currents, and gravity/loss of velocity. It's also possible to see the subsonic transition with jacketed bullets, brief blur of the copper streak and almost a "puff" of mirage from the shockwave. I didn't note this with cast, not certain that the ones I saw were going subsonic at the ranges being observed. Now, the persistence of human vision is a measureable constant, and the frequency of the helix, if anywhere near the rpm (and it would practically have to be, or an order above or below that frequency) of the boolit's rotation, would exceed that persistence by many, many times, and the boolit would appear simply as a grey blur the size of the helix spiral diameter. I can clearly see the boolit as its actual size diameter-wise (but a streak a few feet long) right until it punched the target, so I don't believe that any of the boolits or bullets I've ever observed at long distance followed a helical path anywhere near the size of the groups on the target. No doubt the physics dictate that the boolit/bullet will rotate about it's center of mass once out of the barrel and follow a "corkscrew" path, but I think that the helix would be measured in fractions of an inch, maybe only a few percent of boolit cross-section, rather than inches or feet. Comments?

I just think that there is something else is going on here, not just RPM. I find most fliers caused by lube or powder-fouling purging from the barrel, or just plain old bad boolits once in a while. I find regular ol' lousy groups caused by something going awry at launch, most commonly in my case poor boolit fit and excessive chamber neck clearance. In fact, assuming decent powder/boolit/cartridge combinations, I find excessive chamber neck clearance or eccentric static boolit body/bore alignment to be my biggest detriment to achieving accuracy with regular, unpatched boolits. Lube has it's limitations, some earlier than others in the velocity world. Here I gotta poke a little fun and say facetiously that your whole theory of RPM threshold is really just a mistaken observation of the accurate velocity limits of Javalina Alox! (I know you've done your homework on lubes, but so have I). Alloy, of course, is a factor. I'm beginning to think that barrel harmonics has more to do with HV limits with cast than has previously been thought, at least my me.

Gear

[303Guy]

Thanks Larry.

What I meant by 'grey area' was that it is not a sharp cut-off point but rather an increasing degree of boolit instabilty as velocity increases.

What I find useful in the RPM thrshold hypothesis is the difference of normally expected accurate velocity versus rifling twist rate.

What this tells me is that to maximise performance from a given twist barrel, I need to select an appropriate boolit weight. The faster the twist, the heavier the boolit and lower the velocity.

[crabo]

Trying to understand all of this makes my head hurt, but there is an interesting article in July Rifle Magazine by John Haviland on the 220 Swift. He quotes Lester Womack in P.O. Ackley's Volume 1 Handbook for Shooters and Reloaders about the 220 Swift.

It is Womack's opinion that the 220 Swift was far superior to all of the cartridges used in a burro culling operation that weighed up to 600 pounds.

Womack contends that the reason for the Swift's "phenomenal sucess" was the bullet's fast rotational spin. "Velocity falls off rapidly due to air resistance, BUT, the bullet loses very little of it's rotational spin during its entire flight... As a bullet enters an animal. at any range, and begins to upset, the centrifugal forces cause it to go to pieces- with devastating effect"

Now if I am following this discussion correctly, we are talking about accuracy vs wound channels, and cast boolets and not bullets, but I thought I would throw this tidbit in the mix.

[geargnasher]

Crabo, I've heard reports of .22 caliber j-words being fired at such velocity as to disintegrate upon muzzle exit.

Gear

[303Guy]

I've often wondered about the influence of spin in wound effects. Then I started using my hornet with its 1 in 16 twist which made me think spin had no influence on penetration or wound effects. I had a mini-14 with a 1 in 10 twist and shot bullets to the same velocity. However, if a boolit driven to its RPM threshold it may well play a major part in wound effects.

[geargnasher]

The boolit will only be making one rotation per X number of inches, even at half the muzzle velocity in a 9" twist it's only going to make one revolution in 4-1/2", not exactly a tornado. The action of boolits buzz-sawing their way through a target, in my opinion, is highly overestimated.

Gear

[303Guy]

The action of boolits buzz-sawing their way through a target, in my opinion, is highly overestimated.Yes, that's a total myth. But a boolit that is spinning fast enough to be only just staying together might just blow up with the additional forces of impact. I don't know, it's just a question.

(I can see Larry is going to be kept busy with this thread! :mrgreen: )

[lwknight]

303 , the rpm will be reduced my mass expassion instantly. I'm too tired to articulate this idea thoroughly but its like a gyro-pendrulem effect. An object spinning in its own energy will slow down as the object expands because a longer radius off the axis would have more energy and since its rotational energy is limited to what you gave it in the barrel it has to slow the rate of spin.

Conversly , things spin faster if they get squeezed tighter like the things in the toilet whirl faster as it nears the vortex

[crabo]

Crabo, I've heard reports of .22 caliber j-words being fired at such velocity as to disintegrate upon muzzle exit.

Gear

I think it has something to do with the jacket being designed for a slower velocity while being used in a higher velocity platform.

[303Guy]

303 , the rpm will be reduced my mass expassion instantly. I'm too tired to articulate this idea thoroughly but its like a gyro-pendrulem effect.Got it! A light just went on. Thanks. That explains quite a bit.

[Tatume]

The boolit will only be making one rotation per X number of inches, even at half the muzzle velocity in a 9" twist it's only going to make one revolution in 4-1/2", not exactly a tornado. The action of boolits buzz-sawing their way through a target, in my opinion, is highly overestimated.Gear

If the barrel has rifling of one turn in nine inches, the bullet will make one turn in nine inches at any speed. Further, rpm decreases only slightly over the time the bullet is in flight. There is very little air resistance to rotation of a bullet. But you're right, the "buzz-saw" cartoons we saw during the misinformation campaign against Black Talon ammunition were completely false.

[44man]

Gear, I used a 60 gr Hornady in my 220 Swift long ago for long range. It was a thing to see when it hit a crow at 400 yards, wings came out of the tree!
I was shooting at paper one day and did not see a hole. I walked down to find the paper full of little shrapnel holes. Back stepping a foot, I found one blade of grass cut off.
Now the helix thing. I watched thousands of bullets go down when I shot IHMSA.
Using the 240 gr bullet in the S&W 29 always showed the helix and it was pronounced. The bullet was super accurate at all ranges and would consistently shoot 1/2" at 50 meters. The only thing we ever seen was if distance was changed a little the POI would shift about as much as the helix.
Just going to a 250 gr bullet eliminated the helix.
The strangest boolit was from the 30-30 TC. Watching it being shot at 200 meters, the boolit would curve way to the right halfway down and it looked like it was going to hit the next ram in line, then it would swing back and hit the ram aimed at. Wind or no wind or from any direction did not change that. This boolit needed different windage settings for different ranges.
Yet with a scope on the gun from bags I could hit pennies at 100 meters. It was strange to shoot pennies at 100 meters from a pistol with a cast boolit but I could do it over and over.

[Bret4207]

Larry, your persistence and gluttony for punishment is admirable. Nothing wrong with that friend!

You mention obturation in the explanation and speak of imbalances. I can agree with at least part of that whole heartedly. Controlling obturation by using a properly sized boolit, IMO, will always give better, more predictable results that depending on obturation mashing the boolit into putty and then hopefully fitting the grooves. Same thing for alignment. An off centered boolit isn't likely to be more accurate than a well centered one.

As for the RPM theory itself, it makes sense to me that there is a point where a spinning object exceeds it's capability of remaining stable. Where and how that occurs...got me.

[44man]

Watching bullets and boolits do the strangest things is hard to believe. Yet none of the goofy stuff ever affected accuracy and most shot better then bullets going in a straight path.
The same thing about a WFN not being able to shoot distance, it is just not true. They were just shot wrong.
To shoot 1/2" down to 1/4" groups at 100 meters with a 10" barrel Contender 30-30 and cast is not possible either---or is it?

[Junior1942]

In my considerable cast bullet experience (CCBE??) with MY ACWW alloy, as a bullet exceeds 120,000 RPMs and heads toward 150,000+ RPMs, two things happen simultaneously: (1) groups start becoming patterns; and (2) bullet holes in the paper target start containing commas.

The commas are caused by the ridges between lube grooves separating from the bullet. Think of a Q shaped bullet hole. Larry is 100% correct.

[44man]

I have always believed under spun bullets are the worst. They give up accuracy with range too fast.

[pdawg_shooter]

In my considerable cast bullet experience (CCBE??) with MY ACWW alloy, as a bullet exceeds 120,000 RPMs and heads toward 150,000+ RPMs, two things happen simultaneously: (1) groups start becoming patterns; and (2) bullet holes in the paper target start containing commas.

The commas are caused by the ridges between lube grooves separating from the bullet. Think of a Q shaped bullet hole. Larry is 100% correct.

I have recovered a number of 311284 bullets from my berm and none had missing ridges. These were fired at just over 3000fps with a 1 in 10 twist. They were supported in the barrel with a paper patch that prevented distortion due to acceleration. The bullet noses were mangled but the shank was near perfect. That is 216,000rpm if my math is correct. I use a slow powder that gives me near 100% load density and the most gentle acceleration possible, maybe that is why one powder shoots better than another. Accuracy was just under MOA.

[geargnasher]

If the barrel has rifling of one turn in nine inches, the bullet will make one turn in nine inches at any speed. Further, rpm decreases only slightly over the time the bullet is in flight. There is very little air resistance to rotation of a bullet. But you're right, the "buzz-saw" cartoons we saw during the misinformation campaign against Black Talon ammunition were completely false.

Incorrect. The number of turns per distance traveled is variable because it is a function of TIME. If a boolit makes one turn in nine inches after leaving the muzzle, and it hits a target downrange going half the muzzle speed, the boolit will still be rotating almost the same number of turns per minute as when it left the muzzle, but going half the distance in the same amount of time, so it will turn almost one revolution in 4.5 inches as it enters the target.

Take a cordless drill with a bit in it. Hold the trigger wide open and jam the bit into a board as fast as you can, then do it normally. Note the effect.

Gear

[Larry Gibson]

Gear

The paper patch on the cast bullet is like a jacket; it does support the bullet. Pdawg's post in this thread is absolutely correct. I have shot enough PP'd cast bullets to know that also.


I have recovered a number of 311284 bullets from my berm and none had missing ridges. These were fired at just over 3000fps with a 1 in 10 twist. They were supported in the barrel with a paper patch that prevented distortion due to acceleration. The bullet noses were mangled but the shank was near perfect. That is 216,000rpm if my math is correct. I use a slow powder that gives me near 100% load density and the most gentle acceleration possible, maybe that is why one powder shoots better than another. Accuracy was just under MOA.

The PP does support the bullet and prevent collapse of the lube grooves. A collapsing lube groove or grooves on one side can also cause the nose to slump to one side (a well observed/documented fact with unsupported nose bore riders). I’m sure that Pdawg will tell you here as he has reiterated in other threads that the faster you push (increased acceleration) the harder the alloy must be to prevent unwanted and uneven obturation, setback, sloughing, etc. Remember also that the obturation, setback, sloughing, etc most often do not happen evenly around the bullet. However I believe much of the success with softer AC’d alloys some are using at HV is because they do tend to obturate, setback, slough, etc. more evenly around and throughout the bullet during acceleration. They maintain a better balance that way.

The point being here is the PP does support the cast bullet and prevents unwanted unbalancing of the bullet during acceleration which is why it can be driven faster, at higher RPM than the regular unsupported cast bullet.

How “significant” do you think the helical spiral is? DRB seemed a bit confused (he never answered my query one way or the other) as to bullet rotation (the spin to stabilize the bullet) and the helical spiral. The spiral may take several hundred yards to complete. It may be less, it may be more depending on the degree of imbalance of the bullet and the amount of centrifugal force to act upon that imbalance. If the imbalance is small enough and the centrifugal force isn’t high it may not complete a spiral at all during the bullets flight. I also have watched enough cast bullets in flight at long range and have seen the helical spiral, not a complete spiral but a partial one. On the other hand I have seen complete helical spirals on very long ranges where .50 cals were in use. One can observe tracers at long range begin to spiral around the flight path as the tracer element burns out and the bullet becomes unbalanced.

Go back to my above description and in the quoted portion you will find;

“ It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.”

That is not my theory, thesis or what ever you or anyone else wants to call it. That is straight from most every ballistics book or manual. It is well known, factual and understood by ballisticians. Unfortunately many here who want to discredit the science of ballistics have not really studied the subject.:cry:

Of course there are “other things going on”. All of the “other” things you mention are what causes the bullet to be unbalanced. But then realize that once in flight it is the increased RPM that increases the centrifugal force to act upon those imbalances in the bullet that causes inaccuracy or those pesky little flyers. We can shoot those bullets up to a certain velocity/RPM quite accurately but at a point in the higher rate of acceleration we create enough imbalances for the higher RPM to adversely affect accuracy in flight. That is where the RPM threshold is.

Let’s go back to the balanced tire vs the unbalanced tire. As we look at the rotating tire imagine that we are looking at a cross section of the bullet. The center of the hub is the center of form. With the balanced tire we can increase the speed which increases the RPM. Since the tire is balanced the center of spin and the center of gravity of the tire coincide with the center of form. Correlating that by increasing the speed of the tire is the same as increasing fps of a bullet which increases the RPM of both. Thus with a balanced tire we can increase the speed/RPM to a very high rate and the tire will spin smoothly. If it were a balanced bullet it would shoot accurately.

Now let us consider the unbalanced tire. If you not ever driven a car with an unbalanced tired then go pop off the WWs off on of the front tires and drive it up to 70 mph or so and you will experience the phenomenon. No, don’t really do that but those who have driven with unbalanced tires are well aware of what I am describing. As we observe the unbalanced tire spinning we can see that up to a certain speed/RPM it spins smoothly. However, as we increase the speed/RPM at a certain point it begins to wobble. With my old ’56 Ford that was around 30 mph. This is because with the unbalanced tire the center of form remains the same at the center of the hub. The center of gravity is moved out because the tire is not balanced and the center of gravity is rotating around the center of form. This also moves the center of spin away from the center of form which is what was causing the initial wobble at a certain speed/RPM. The centers of spin, form and gravity most often are not coincidental in the unbalance tire or an unbalance bullet either.

As speed/RPM increases the tire begins to hop, with the old ’56 Ford this was around 50 – 55 mph. This is the point where the centrifugal force over comes the rotational stability and the helical spiral begins, i.e. the RPM threshold. Note that the helical spin is at a much, much slower rate that the rate of spin of the tire. As we increase the speed/RPM of the unbalanced tire even more we see the “hop” (helical spiral) of the tire gets larger and much more pronounced. The rate of rotation of the helical spiral is much less that the rotational spin of the tire. The very same phenomenon happens with cast bullets and even jacketed bullets.

Where does, or at what speed/RPM does the “wobble” and the “hop” begin? That obviously depends on the size of the tire, the degree of imbalance, how for the centers of spin and gravity are from the center of form and how far they are from each other. There is no exact speed or RPM. The do know that around 25 – 30 MPH the tire will begin to wobble and at some speed/RPM it will begin to hop. It’s the same with a cast bullet; around 120,000 – 140,000 RPM they will begin to “wobble” and at a higher RPM they will begin to “hop”. The “wobble” is where group accuracy begins to deteriorate and the “hop” is where it goes completely bad as in patterns instead of groups.

A completely unbalanced tire will wobble and hop at a low speed/RPM. If we partially balance the tire it won’t wobble and hop until a higher sped/RPM is reached. The perfectly balanced tire (centers of form, spin and gravity coincide) won’t wobble or hop at all regardless of the speed/RPM because the centrifugal force is radiating equally in all directions. It is the same with bullets; we mitigate the wobble and hop by keeping them as balance during casting, loading and acceleration as possible. The better balanced the bullet the higher the speed (fps) and RPM we can shoot them accurately at.

If we had 10 perfectly balanced cast bullets on exit from the muzzle, given all other things being correct, then we could shoot them very accurately regardless of the RPM up to the structural strength of the alloy. Some here have and do claim to cast and shoot perfectly balanced bullets. They do up to a point. All will admit that at some point accuracy goes. So guess what? That’s the point at which their perfectly balanced bullets are not perfectly balanced anymore and they have found the RPM threshold with their bullets and components.

Larry Gibson

[Tatume]

Incorrect. The number of turns per distance traveled is variable because it is a function of TIME. If a boolit makes one turn in nine inches after leaving the muzzle, and it hits a target downrange going half the muzzle speed, the boolit will still be rotating almost the same number of turns per minute as when it left the muzzle, but going half the distance in the same amount of time, so it will turn almost one revolution in 4.5 inches as it enters the target.

Take a cordless drill with a bit in it. Hold the trigger wide open and jam the bit into a board as fast as you can, then do it normally. Note the effect.

Gear

You're right, sorry.

[Larry Gibson]

Incorrect. The number of turns per distance traveled is variable because it is a function of TIME. If a boolit makes one turn in nine inches after leaving the muzzle, and it hits a target downrange going half the muzzle speed, the boolit will still be rotating almost the same number of turns per minute as when it left the muzzle, but going half the distance in the same amount of time, so it will turn almost one revolution in 4.5 inches as it enters the target.

Take a cordless drill with a bit in it. Hold the trigger wide open and jam the bit into a board as fast as you can, then do it normally. Note the effect.

Gear

Gear

You hold a common belief that is incorrect. The RPM of a bullet is determing at exit from the muzzle. It is a function of twist and velocity and is pretty much "fixed" on muzzle exit. The Bullets RPM slows down very, very little over a bullets flight, even at maximum range. It is not a function of nor affected by velocity decay down range.

Originally Posted by Tatume
If the barrel has rifling of one turn in nine inches, the bullet will make one turn in nine inches at any speed. Further, rpm decreases only slightly over the time the bullet is in flight. There is very little air resistance to rotation of a bullet.

Tatume, you were correct.

Larry Gibson

[44man]

Time is important. Revolutions per MINUTE.
However the helix a boolit exhibits might not be due to imbalance at all. I have seen it with the best bullets made.
Bullets will go to sleep after velocity drops and to just say it comes into balance might not be correct.
Bullets not spun up enough will be good at close range but will stray farther and farther at longer ranges.
I am afraid to blame it on out of balance bullets.
Take the most perfect bullet made and it will exhibit these traits.

[felix]

What's amazing, is how much energy it takes to get a boolit up to the terminal RPM. Up to a third of the amount given to the VELOCITY. ... felix

[Larry Gibson]

44man

Bullets with yaw and nutaions are the ones that can "go to sleep". That is not the same affect as the helical spiral caused by centrifugal force on an imbalance. It may appear to be so at short range but the two are different. The yaw and nutation causes settle out and the bullet "goes to sleep" with accuracy being better within 100 - 300 yards. With the helical spiral it gets larger as range increases (non linear group expansion as range increases) and the bullet does not "go to sleep". Two different affects. The most "perfect bullets" that exhibit that are from over stabilization (causes yaw) or a muzzle crown defect (creates the nutation).

Larry Gibson

[geargnasher]

Larry, your grasp of basic physics is much weaker than I ever imagined. Velocity and RPM are both a function of TIME (rounds-per-minute, feet-per-second), where time and rotational velocity are considered constants (in non-relativistic physics). Actually, velocity itself is a functon of time, whereas acceleration/deceleration would be the second derivative.

Now, you say that the boolit's rotation per distance is fixed, right? Like the barrel itself is three hundred yards long, and the boolit tracks the same rotational path from muzzle to target, regardless of velocity. You also say that, for practical purposes, the boolit's rotational velocity doesn't decay, right? Those two things can't exist simultaneously unless the boolit is traveling the same speed at the target that it was in the muzzle. Savvy? There are four factors: Rotational velocity, forward velocity, (actually a formula of increasing deceleration), distance, and time. The laws of freshman algebra dictate that if you change one thing (in this case, forward velocity) you must balance the equation, in this case by increasing the rotational velocity with regard to time/distance.

Let me put it another way. You're drilling cull burros with a 220 Swift. Your muzzle velocity is 3000 fps, the twist is one in nine. The burro is two feet across. If you shot the burro point-blank at 3000 fps, the bullet would make 2-2/3 revolutions through the burro. Your impact velocity is 2000 fps at, say 300 yards, but the rotational velocity is still a function of time, and is still turning practically the same amount of RPM, only velocity (distance traveled in a given time period) is LESS. Therefore, at 2000 fps, the boolit that was traveling at a rate of 4,000 rotations in 3,000 feet at the muzzle is now traveling at a rate of 4,000 rotations in 2,000 feet, and will be making one rotation in SIX INCHES instead of one rotation in NINE INCHES that it was at the muzzle. When the bullet passes through the burro, it will make four revolutions going through instead of the 2-2/3 it would have made at point-blank.

Your error is that you forget that both rotational velocity and RPM are variables,or functions (fX), directly related to time and distance NOT fixed values, and even excluding the derivatives involved with negative acceleration and taking only two-foot snapshots of distance at muzzle and impact points you can see that the function of time is the factor you and Tatume forgot about.

Gear

[44man]

Larry, I watched thousands of bullets and never seen "yaw", only the helix around the original flight path. Bullets never shown other then the base to me. No wobble of the bullet.
Yaw is real, no doubt but this was not the case. There was no degradation of accuracy.
I showed the 30-30 boolit and how it shot. I ran out of gas checks one time so I loaded them anyway. Every single boolit went through the paper sideways at 50 yards. I would call that yaw. I went outside the limits of boolit length to twist to velocity. There was nothing wrong with the boolit except it did not fit anymore. Yes, the lack of the GC length changed the boolit into a scud.

[303Guy]

I've seen yaw. Not in flight but the imprint it makes on paper. The holes have a slight 'feathering' on one side or the other, mostly random.

I'd suggest that the amount of yaw that causes the spiral patch is very small and would not be visible. By 'yaw' I mean the slight boolit misalignment with the flight path that has the same rotational speed as the helix itself and is an effect of gyroscopic forces. (Support a spinning gyro on one side and it will slowly 'spiral').

The yaw Larry is refering to is the yaw caused by an internal imbalance of the boolit due to uneven mass distribution and has the same rate as the spin. That would cause a spiral path that opens up exponencially. That's the yaw that makes the non-round holes on paper.

I would think that the likelyhood of complex spiral paths would exist with an imbalanced boolit.

[geargnasher]

As far as yaw goes, I've shot some decent groups with oval holes, and often the ovals were indicating yaw in the same direction, in other words true yaw, not wobble unless the wobble was miraculously synchronized at impact.

On to the Helix. I thought of a perfect analogy that just about every american male between the ages of 6 and 90 should have witnessed at some point in their lives: The spiral of a well-thrown football. Footballs have a built-in embalance at the laces. When thrown with a good, balancing spiral rotation the football will trace the path of a helical spiral as it wobbles about it's center of mass, which is off the center of axis by about an inch. This may be compounded by the forces perpendicular to the line of departure imparted by the quarterback's fingers as he rolls his fingers downward to wind the ball into the spin as he releases it, but the ball has a natural tendency to "go to sleep" after a few yards and settle into a consistent helical path. At some point, say if the football were fired from a pumkin cannon at speed great enough to exceed the RPM threshold of the football, it might go wildly out of control. This analogy, together with your "tire" analogy, show two things: That unbalanced rotating objects have limits to stablity, and that the helix they follow is directly related to the rate of revolution or a order therof. Also, the diameter of the helical path is less than half the cross-section of the object up to a point, then the path can go wild. Does that pretty much sum up your theory?

I think you could make a lot more sense with your theory if you considered a factor called "resonant frequency". You talked all around it with your tire analogy but didn't ever mention it. I've forgotten more about road force variation, match-mounting, dynamic and static balance combined with damping rate and unsprung mass vs. sprung mass of vehicle than most folks probably ever even thought of, so let me explain what I mean about resonance. A tire/wheel/suspension assembly moves as a unit. It's interesting to note that most dynamic road force variances (think soft spot or knot on a tire) usually occur at 30 mph, regardless of tire size, wheel size, suspension type, or type of vehicle. A 10K lb 4x4 diesel pickup with 37" MT Boggers will start to shake at the same SPEED (albeit a different FREQUENCY) that a Honda will if there is a knot on the tread. This factor will usually occur again in the next order of the harmonic, that being TWICE the rotational velocity, and in the case of a tire in contact with the road, twice the vehicle speed. At the next order, 120 MPH, the tire explodes. It's RPM threshold being exceeded. Compare that to a static embalance, which is really what we have with boolits. A tire-wheel assembly that is out of static balance will usually start to vibrate at 35 mph, smooth out, and do it again at 70. This seems more related to tire size than road force variances, I think because it's more direct and constant of an embalance than tire tread variances. On a small tire a balance problem might show up at 25, 50, and 100, while larger tires might tramp at 45 and nobody has reason to find out if they do so again at 90. What I'm driving at here is that an unbalanced boolit will behave in a very predictable manner up to a certain point based upon it's resonant properties, and if you want to gain some credibility to your theory and make it useful, it would be a simple matter to develop an equation where a person could determine first the resonant frequency of a given boolit, then enter values for twist rate, muzzle velocity, etc. into an equation and get a viable "threshold number" that they can expect to achieve with accuracy.

You also don't explain why the helix, if it is reponsible for blown groups according to your theory, doesn't make circular doughnut patterns on the targets. If a boolit only makes one or two spirals of the helix between muzzle and target, then that isn't responsible for blown groups at all. It might explain why groups get printed in different places on the targets at different distances, but not blown groups. I can understand that a wild loss of stability at a certain point in the RPM spectrum would blow groups, but if it's a predictable, ever-growing helix it would only move the point of impact, not print a group the size of the helical sprial at one distance, unless the helix was making a revolution about every ten feet and the ES of the velocity was equal to that 10 feet or close. In that event the group patters would be doughnuts, anyway, as I already mentioned. Bascially I don't buy your helix theory of embalance causing non-linear group dispersion above the RPM threshold because, based upon what we do know to be true and documented, the patterns on paper don't reflect it. Also, I don't buy it because an identical boolit that's PP'd can be fired at higher velocity and don't pretend to tell me that it isn't subject to the same external forces that an unpatched one is. Paper won't save a boolit nose from slump, especially if the nose isn't patched, and I challenge anyone to show me recovered samples of PP'd GG boolits vs. unpatched GG boolits fired from the same gun at the same velocity where the patch prevented GG collapse or any other damage being done to the boolit during it's trip down the bore except possibly more secure engraving. This overwhelmingly convinces me that RPM has very little to do with accuracy deterioration from 100k to 200k rpm, that there is something else like barrel whip, muzzle exit tip, or deformation at muzzle exit. The only other thing I can think a PP does to increase usable velocity is gas seal and helping the boolit fit the throat so it doesn't deform on launch by creating a cushion around it.

Here's a good test of the theory. Take jacketed bullets and deform them, either by bending the noses slightly, or by drilling small holes in the side of the jacket to create an unbalanced condition. Then observe the RPM limits and patterns on the targets of THOSE. If the theory is true, similar limits should be observed as we commonly note with cast boolits. They should shoot accurately to 120k-140K rpm, then go to hell suddenly, just like cast. If the group dispersion is more linear with regard to rpm increase, then we can assume that there is something else going on with cast than just the effects of imperfections showing up catastrophically at a certain RPM.

Gear

[geargnasher]

What's amazing, is how much energy it takes to get a boolit up to the terminal RPM. Up to a third of the amount given to the VELOCITY. ... felix

....Which offers an explanation of why any kind of jacket, be it copper or paper, offers better performance by increasing the bearing strength of the engraved portion so the unit can resist the torque forces imparted by the lands without deforming too badly.

Gear

[303Guy]

I was shooting at paper one day and did not see a hole. I walked down to find the paper full of little shrapnel holes.44man, how far was the paper target? Did you do any tests to determine at what distance the boolit came apart? And how far it was effective in crow after it had come apart?


I've shot some decent groups with oval holes, and often the ovals were indicating yaw in the same direction,That supports 44man's account of the S&W 29 and the 30-30 TC.

[para45lda]

Not to sound retarded ( my head is hurting from all this. It's been a while since school) but can you share the formulas you're using? I've got one differed out but would lime to make sure im understanding correctly.

Wes

[Bret4207]

Incorrect. The number of turns per distance traveled is variable because it is a function of TIME. If a boolit makes one turn in nine inches after leaving the muzzle, and it hits a target downrange going half the muzzle speed, the boolit will still be rotating almost the same number of turns per minute as when it left the muzzle, but going half the distance in the same amount of time, so it will turn almost one revolution in 4.5 inches as it enters the target.

Take a cordless drill with a bit in it. Hold the trigger wide open and jam the bit into a board as fast as you can, then do it normally. Note the effect.

Gear

Okay, I read the response further down the page and this is just confusing. Twist is not RPM, time has nothing to do with twist. But you aren't saying that a 1/9" twist boolit, no matter what the speed, is somehow going to be going appreciably slower than 1 turn in 9" are you? I can see some rotational slowing but it's not much in, say, 100 yds. So please clear this up for me because what you said makes zero sense to me.

[onceabull]

to the time to introduce the "expert"at Sierra Ballistics cited by the great "starmetal" in support of his idea that the twist rate wasn't fixed by the the rifling twist but got greater and greater as it whistled down range in that E.Tennessee air.. Maybeso some should call the physics teacher at the local High School.. Onceabull

[357shooter]

Aren't the two time measures completely disconnected, with no relationship to each other. One being RPM, which is a result of twist and bullet velocity when the bullet exits the barrel. The RPM doesn't change much, and the velocity no longer has an impact, out of the barrel.

Two is bullet velocity in FPS. That can decrease significantly over a long range.

Since there is no direct connection, out of the barrel, the RPM decreases little, the velocity decreases much more.

Tying them together confuses the issue.

[onesonek]

Crabo, I've heard reports of .22 caliber j-words being fired at such velocity as to disintegrate upon muzzle exit.

Gear

I have heard such also.
While I haven't tried it in a deliberate sense,,, I loaded up some 35 grainers designed for the Hornet once in my Swift,,,,, guessing 4000 fps.
At initial sight in, at the range of first line of sight crossing of about 38 yds iirc, after the first shot I could see, what I would call a vapor trail of lead surrounding the bullet hole. It did have a slight spiral pattern, that means anything.
I can't say more velocity added, would have resulted in total disintegration. But suspect it is possible, as they were not designed for that velocity, with their light jackets and a fair amount of exposed lead.
I didn't persue it further to find out, as they did fine, for near vaporization of the 13 Stripped diggers, at 3500 out of the .223. Which is still close to a 1000 fps faster than intended.

[Larry Gibson]

Gear

I’m going to suggest you research rate of spin as it relates to bullets. You will find that the rate of spin of bullet deteriorates very little as range increases and velocity drops. That is a fact. A thrown football, regardless of the quarterback, comes no where near the RPM we are talking about. Not a good analogy at all. As I explained to 44man, a bullet “going to sleep” is a different aspect of ballistics and not the same as the RPM threshold, apples and oranges.

BTW; the bullet will make more turns in the donkey but the RPM of the bullet remains the same. Spin a top on a small stool. Now quickly lift the stool 6 feet. Does the RPM of the top increase? Now low the stool very quickly. Does the RPM decrease? It does neither because the RPM of the top will remain relatively constant whether the top is moving in either direction. You correctly answer your own argument here with “a rate of 4,000 rotations in 3,000 feet at the muzzle is now traveling at a rate of 4,000 rotations in 2,000 feet”. The bullet is making the same 4000 revolutions (that’s the same RPM) regardless of the distance. You really do need to read up on this in a good ballistics book or manual.

You’re reading more into the tire analogy than is there. Jack the car up and spin the tires free of road surface and the same thing I described will happen.

An equation? So why then can’t you or DrB come up with an equation that will tell us the exact velocity at which a .308W with a 150 gr bullet will get the best accuracy? You can't. Once again you, like DrB, want an exact RPM figure or a way to figure exactly at what RPM the threshold will be reached and will happen. As with an equation to tell us exactly at what fps accuracy will occur, it doesn’t work that way. I have already explained that the reason is the variables.

But once again; we can assume with a regular cast bullet with a BHN of 15 -18 in a medium capacity case using a medium burning powder that the bullet will reach the RPM threshold between 120,000 – 140,000 RPM. That is based on my 45+ years of shooting such and 45+ years of observing the same with other shooters. Many here like felix also agree. No equation, no way to determine the exact RPM when that set of components in that particular rifle under the conditions tested comes up to the threshold other than to test it.

Again; the helix is not my theory. The helix is a ballistic fact. If you would research it in a ballistics book or manual you will find that out. I suggest Understanding Modern Ballistics by Robert A. Rinker for those just beginning a study of ballistics. A better understanding of ballistics might enhance the credibility of your statements.

In the above post to you I explained that the helical spiral may take a long distance to even make a significant arc around the flight path. I also explained that it may not spiral but may simply go off on a tangent (the “blown group” you refer to. Many here have pushed cast bullets to the point they don’t even print on target anymore because the group is so large. The definition I posted in quotations and italics in this thread in above posts and the other thread explain it quite well and is a direct quote from a ballistics manual. It is not my theory; again should you bother to research it you would find out. “Donut patterns”; what is the “distance to the target” are you talking about? Just how many helical spirals do you perceive happen between muzzle and 100 yards, or 200 yards? The helical spiral may take several hundred yards if not more to be noticeable (probably why those who say they haven’t seen it haven’t seen it), it may take far more range than that and as explained it may not make a complete spiral to the maximum range of the bullet. As already explained; it depends. By “donut” patterns” you have perceived something happening that I have not said does and, in fact, explained doesn’t. No, there will not be “donut patterns” on the target at any reasonable range we shoot cast bullets at and I’ve never indicated there would be “one or two spirals of the helix between muzzle and target”. You perceive that apparently and your perception is not correct.

I’m sure Pwdawg or others on the PP forum can satisfy you needs for pictures. However, why don’t you test them and find out for yourself rather than hypothesis how it can't be? I have already explained on this thread and others the difference between a PP’d cast bullet and a naked one. Pwdawg is probably the most experienced here at shooting PP’d cast bullets at HV and he has also told you the difference on this thread. You are free to believe what you will but the facts supporting the differences are readily apparent.

“Here's a good test of the theory. Take jacketed bullets and deform them, either by bending the noses slightly, or by drilling small holes in the side of the jacket to create an unbalanced condition. Then observe the RPM limits and patterns on the targets of THOSE. If the theory is true, similar limits should be observed as we commonly note with cast boolits. They should shoot accurately to 120k-140K rpm, then go to hell suddenly, just like cast. If the group dispersion is more linear with regard to rpm increase, then we can assume that there is something else going on with cast than just the effects of imperfections showing up catastrophically at a certain RPM.?"


I already ran that test for Bass Ackwards several years back. I used M118SB ammunition in a 10” twist .308W rifle. I shot 10 shot groups at 50 yards, 100 yards and 200 yards with unmodified bullets. I then drilled on .3 gr of the bullet out on the side of 30 more rounds. I then fired the same 10 shot groups at 50, 100 and 200 yards. The expansion of the regular unaltered M118SB was predictable and linear between all ranges. The non linear group expansion of the altered M118SB was also predictable; a small difference between 50 and 100 yards and a large non linear expansion between 100 and 200 yards.

I also, as reported to DrB on his thread, conducted basically the same experiment using the 311291 in an ’06 one load was below the RPM threshold at 1912 fps (136,400 RPM). The 10 shot groups with that load at 50, 100 and 200 yards were .7”, 1.3” and 2.5” restively. That is quite normal linear expansion. The next load was the same bullet loaded over the RPM threshold at 2500+ fps (179,400 RPM). The groups at 50, 100 and 200 yards were 2.55”, 4.7” and 14.5” respectively. What we see there is little non linear expansion between 50 and 100 yards but a very large non linear group expansion of 14.5” at 200 yards. I have run similar test so many times with a variety of cartridges and twists over the years. The results are the same; exceed the RPM threshold and groups open in a non linear fashion as range increases.

If you would care to conduct your own tests in an attempt to prove your own thesis/theory correct then feel free to do so and report back your findings. Better than using a jacketed bullet why don’t you do the same test with a cast bullet? That would be more relevant here as we are discussing the RPM threshold as it relates to cast bullets. As to jacketed bullets I suggest you read any one of the later Hornady loading manuals (try page 29 of the current, 8th Edition Horandy manual). Again, not my “theory” here but quoting directly from the ballisticians at Hornady;

“ As long as the bullet is in the barrel it rotates around its center of form but when it leaves the barrel it spins around its center of gravity and this causes it to veer slightly off its intended course at a tangent to the spiral described by its center of gravity as it went up the bore.”

Sound familiar, like what I stated/quoted and have been saying all along? Gear, you may be smarter than me, DrB may be smarter than me and some others here, but do you think you or any of them are smarter than the ballisticians at Hornady who have put that out in millions of reloading manuals? Again, it’s not my “theory”, it is ballistics.

I have conducted enough tests to prove the RPM threshold does exist, particularly with cast bullets, and what happens when it is exceeded. I suggest you conduct some of your own test then study up on ballistics before hypothesizing erroneously.

Larry Gibson

[Larry Gibson]

Put a Hornady 55 gr SX or the Sierra 50 gr Blitz out of a 9" twist or faster above 3200 fps or so and you will many times see a grey "smoke" trail behind the bullet or a puff of grey at 30 -50 yards where the bullet comes apart. The Speer 52 gr HP out of a 7" twist AR at 3200 fps will many times make a "banana peel" hole through a 25 yard target and won't make it to a 100 yard target.

This has nothing to do with the RPM threshold as such. It has to do with the centrifugal force over coming the structural integrety of the very thin jackets and soft lead cores.

Larry Gibson

[geargnasher]

Okay, I read the response further down the page and this is just confusing. Twist is not RPM, time has nothing to do with twist. But you aren't saying that a 1/9" twist boolit, no matter what the speed, is somehow going to be going appreciably slower than 1 turn in 9" are you? I can see some rotational slowing but it's not much in, say, 100 yds. So please clear this up for me because what you said makes zero sense to me.

No, Bret, it's going faster. Now before you get freaked out by that, understand that it's all relative to time.

Take a trip with me on the back of a boolit, using some made-up but realistic numbers: You're drilling cull burros with a 220 Swift. Your muzzle velocity is 3000 fps, the twist is one in nine. The burro is two feet across. If you shot the burro point-blank at 3000 fps, the bullet would make 2-2/3 revolutions through the burro. Farther down range, your impact velocity is 2000 fps at, say 300 yards, but the rotational velocity is still a function of time, and is still turning practically the same amount of RPM, only velocity (distance traveled in a given time period) is LESS. Therefore, at 2000 fps, the boolit that was traveling at a rate of 4,000 rotations in 3,000 feet at the muzzle is now traveling at a rate of 4,000 rotations in 2,000 feet, and will be making one rotation in SIX INCHES instead of one rotation in NINE INCHES that it was at the muzzle. When the bullet passes through the burro, it will make four revolutions going through instead of the 2-2/3 it would have made at point-blank.

I don't know why this is such a difficult thing to get. If the barrel went all the way to a 300-yard target with the same twist the whole way, the boolit would have to be going the same forward velocity at the target as it was at the "muzzle" to make the same number of rotations in a given time period. In other words, for the boolit to be maintaining it's same rate of spin at the target that it does at the muzzle (which it essentially does), yet lose velocity (which it most certainly does, and a significant amount), the number of turns traced in a given amount of travel must increase.

Here's another analogy: A propeller on a small aircraft. Sitting on the runway with the brakes set and ready for launch, the prop is wound up tight at takeoff RPM, then the brakes are released and it begins to accelerate forward, maintaining the same RPM as the plane continues to accelerate down the runway. From the plane's perspective, the prop is turning the same speed the whole time, but if there were oil dripping off the prop blades as it went from a standstill to takeoff, the dripmarks on the runway would go from a puddle at standstill to ever-increasing sling marks, and at 150 mph the marks would be much more widely spaced than at 10 feet after launch.

If that doesn't click, how about this: oil is dripping at a constant rate from a leaky pan plug on you car 'cause the lube monkey you took it to for an oil change didn't replace the cracked Nylon gasket. The drip marks on the ground will be closer to each other at 5 mph than they will be at 55 mph. Agree? Of course they will be. The drip was a constant, the forward velocity was not. Same with boolits spinning in the air. If each rotation of a boolit was an oil drip, the drips will be closer together the slower the boolit goes, and as the boolit decelerates downrange, the boolit will be making more revolutions in a given distance, even though it's revolving at virtually the same rate (like the constant oil drip) as it was at launch.

The problem seems to be that some people have the concept that because twist rate and boolit rotation is fixed, it will be so along the entire boolit's path, just like tires on a car in contact with the road. Not the same thing. Here's what you're probably thinking: A tire will rotate at different speeds as the road speed changes, they are fixed to each other. As the car slows, so does the tire, and it doesn't matter if you go a mile at 100 MPH or a mile at one MPH, the tire will make the same number of revolutions. This is not the same thing as the oil drip or boolit in flight. Notice that if the tire makes a mile at one mile per hour, it is turning SLOWWWWW. If it makes the same mile in the same number of revolutions, but at 100 miles an hour, it is turning FAST. A boolit is rotating at the same rate whether going forward at 3000 fps or one fps, but the number of rotations it makes in a foot is much less in 3000 feet than of travel than it is in one foot of travel.

Gear

[onesonek]

"This has nothing to do with the RPM threshold as such. It has to do with the centrifugal force over coming the structural integrety of the very thin jackets and soft lead cores."



I know it's off the topic in relation to cast Larry,,,,,, but.
It is the centrifugal force, that in essence ruins the bullets integrity, caused by running past the rpm threshold of the bullet design So in that sense, they are directly related? Looking at what you noted with 2 different faster twist rates at lower velocity, compared to what I seen with slower twist at higher velocity,,, it seems logical.
As for the cast rpm threshold issue at hand, I haven't the experience to comment, so I'm just reading at this point.

[Larry Gibson]

"This has nothing to do with the RPM threshold as such. It has to do with the centrifugal force over coming the structural integrety of the very thin jackets and soft lead cores."

I know it's off the topic in relation to cast Larry,,,,,, but.
It is the centrifugal force, that in essence ruins the bullets integrity, caused by running past the rpm threshold of the bullet design So in that sense, they are directly related? Looking at what you noted with 2 different faster twist rates at lower velocity, compared to what I seen with slower twist at higher velocity,,, it seems logical.
As for the cast rpm threshold issue at hand, I haven't the experience to comment, so I'm just reading at this point.

I can agree with that; the bullet disintegrating in flight caused by centrifugal force and not making it to the target could be considered "inaccurate" in an abstract sort of way;-)

Larry Gibson

[303Guy]

Gear used the term spin rate. That is not the same as RPM. Well, it could be because RPM is also spin rate. But it is the spin relative to a time frame. Spin rate relative to distance is still spin rate and that will increase down range as the boolit slows its velocity. It's RPM will not increase and Gear did not say it would. There's no reason not to speak of spin rate in terms of distance, after all we speak of rifling twist rate in terms of distance and in his example it is relevant as the buzz saw effect would become more apparent as the boolit slows before striking its target because the spin rate would have increased. Confusing isn't it!:roll:

[onesonek]

Well, that not quite what I meant Larry, but I guess I can see what your saying with your context.

Now as for the rpm threshold with cast, I'm still having a hard time wrapping my head around that totally.
Up to a point, your thoughts make sense to me, if a boolit with some minor balance issues from the mold, and is running at high rpm's, I could see some accuracy issues as a result. But I don't understand how the high rpms are creating a balance problem in flight, unless it's so fast, or rather the cenrtrifugal force is so great, to start having affect on the boolit. Which seems to me, is what your thoughts on threshold, is more about? Yet then when the PP boolit came into the discussion, and shows good accuracy at higher rpm's, ,,,,you lost me at how the paper "jacket" eliminates the balance or centrifugal issues. As when it leave the muzzle, the paper comes off, having no more association with the bullet, at it's higher rpm's well beyond the threshold you speak of. And yet still have very good accuracy, with a softer boolit/alloy to begin with, compared to what is in your notations. Cast is cast, is it not? Not taking into account specific alloy needs for the pressure at hand with a naked boolit.

I guess what I'm saying is, I'm lost. As at first, your arguements for the threshold has some reasonable rationale behind them. But the PP boolit, logically removed the rationale for me, as both boolits are naked in flight.

[leftiye]

How many turns does a bullet fired at 3000 fps make in 100 yards (I'll make it easy 1 turn in 10 inches) -360? (actually it isn't about rpm - yet) And now how many turns does that same boolit spinning at that same rpm. rate (doesn't slow down remember) but traveling at 2000 fps make in 100 yards? The answer is that it turns one turn in 6 inches, roughly. I believe this is what gear is talking about. Rpm remains constant, distance traveled per unit time becomes less and less as the boolit slows down. therefore distance taken to make one revolution is less. If I've got it right this is what geargnasher meant.

[leftiye]

In all of this remember that the greatest force acting on a boolit after leaving the barrel (barring colliding with something) is air resistance. The pressure on the frontal part of the boolit is squared more than five times (each time the speed doubles) when it is accelerated from approx 100 fps to 3000 fps. I don't possess the fluid engineering nor the math to get this exact, but I believe it is close. What needs to be remembered about this squaring is that the square derived from the first doubling is then squared again and then that is squared again and the magnitude of the resulting pressure is truly alarming. Thus terming gaseous engineering "fluid dynamics'.

How close my math comes is immaterial though. You all probly have shot in a 30 knot crosswind and watched the boolit strike a foot or more downwind from where you pointed it at 100 yards. Remember that this is a paltry puff compared to the wind in the face of the boolit (which is about 2160 mph approx.). Short of an unstabilized boolit (ie. "gone") this wind resistance will cause more deflection on a non uniform frontal area than any wobbling effect could cause by itself regardless of cause (poor launch, unbalance. rpm, or indigestion). None of these would have any, or virtually no effect at all in a vacuum.

This by itself amounts to a comment made by DrB saying that to if rpm theory boiled down to saying that a boolit can be spun too fast, then there would be no question (or words to that effect), loosely paraphrased. But larry has in the past claimed that air deflection was not an issue in terms of what he was advocating. Air deflection is what everything relates to. Ironically, like the rpm theory there is also nothing to do about it (except aerodynamic design). Where they are dissimilar is that we are apparently transiting beyond the RPM barrier.

[geargnasher]

Up to a point, your thoughts make sense to me, if a boolit with some minor balance issues from the mold, and is running at high rpm's, I could see some accuracy issues as a result. But I don't understand how the high rpms are creating a balance problem in flight, unless it's so fast, or rather the cenrtrifugal force is so great, to start having affect on the boolit. Which seems to me, is what your thoughts on threshold, is more about? Yet then when the PP boolit came into the discussion, and shows good accuracy at higher rpm's, ,,,,you lost me at how the paper "jacket" eliminates the balance or centrifugal issues. You and me both. I've repeatedly posed the question, since many PP boolits only have a half-jacket and an exposed nose which is still subject to the same slumping forces as unpatched boolits are, and have a plain base which is even MORE susceptable (sp) to deformation than a gas-check, grease-groove boolit, and yet shoot better, faster by a wide margin with little special care in loading than do regular boolit. As when it leave the muzzle, the paper comes off, having no more association with the bullet, at it's higher rpm's well beyond the threshold you speak of. And yet still have very good accuracy, with a softer boolit/alloy to begin with, compared to what is in your notations. Cast is cast, is it not? Not taking into account specific alloy needs for the pressure at hand with a naked boolit. This is exactly my second query from my second post on this thread, and it's one of the main reasons I think "RPM" is a very inadequate explanation for the limits encountered by cast. Larry thinks the paper protects the boolit well enough during launch to account for the great increase in RPM potential, and it might, but what about outside the gun? I understand fully and have experienced the effects on groups of boolits damaged by poor launch conditions or otherwise made imperfect before clearing the muzzle, but internal voids, casting defects, and other balance issues not related to launch damage being attributed to causing extreme group dispersion above a certain RPM would occur whether the boolit is patched or not.

I guess what I'm saying is, I'm lost. As at first, your arguements for the threshold has some reasonable rationale behind them. But the PP boolit, logically removed the rationale for me, as both boolits are naked in flight.

At least I'm not the only one. Nobody can convince me that a piece of notebook paper can be strong enough to prevent lube groove collapse, nose slump, or other launch damage. It can't even prevent such in a base-first sizer under a few PSI, how can it do it in a barrel under tens of thousands of PSI? My conclusion is that the PP isn't raising the limit of "RPM" by supporting the boolit better, or making the boolit more defect-free in flight than any other boolit, it functions by some other means to raise the "threshold", probably merely making a better gas seal and adding some strength to the driving bands. If that's the case, then defects of the boolit aren't responsible for creating the RPM threshold of plain boolits to begin with, there is some other factor at work here creating those limits, probably trailing ege failure, uneven jetting on muzzle exit, or some sort of boolit damage during firing from which the PP protects the boolit. Who really knows for sure? I sure don't.

Gear

[Larry Gibson]

leftiye

Excellent synopsis that is correct. The confusing part is Gear seems to think the rotaional velocity (RPM) does change with regarde to the bullets velocity slowing down at longer range. This is perhaps confusing because he stated.

"The laws of freshman algebra dictate that if you change one thing (in this case, forward velocity) you must balance the equation, in this case by increasing the rotational velocity with regard to time/distance."

Aparently he did not learn about "constants" in freshman algebra. The rotaion velocity (RPM) remains constant as velocity of the bullet slows down. What you say may have been what gear meant but if so he was confusing a lot of us. You are quite correct, thanks for the input.

Larry Gibson

[Larry Gibson]

Onesonek

"Larry thinks the paper protects the boolit well enough during launch to account for the great increase in RPM potential, and it might, but what about outside the gun?"

Consider that the PP does protect the cast bullet, thus there is less unwanted imbalance done to the cast bullet during acceleration (launch). The less unbalanced the bullet is (or the more balanced the cast bullet is) The less the centrifugal force of higher RPM has to act upon and the bullet is more accurate at higher velocity. Basicly simple in that the PP protects and supports the cast bullet preventing obturation, setback, sloughing, etc. to a much higher velcoity. May not be able to convince gear of that but him not being convinced does not make it a proven fact. Perhaps he has some scientific reason why pwdawg can shoot the 311284 PP'd at 3000 fps with excellent accuracy but he nor any one else can/is shooting the same 311284 naked at 3000 fps with equal accuracy?

Larry Gibson

[garym1a2]

Back in 1988 I brought a new Colt H-bar. Had 7:1 twist. Shooting 55grain UMc brand it could not hit anything. I assumed at the time the twist rate made the bullet come apart. As most AR's of the time used 1:12 twist.

I wonder why they came out with the fast twist AR's to use with heavier bullets?


Put a Hornady 55 gr SX or the Sierra 50 gr Blitz out of a 9" twist or faster above 3200 fps or so and you will many times see a grey "smoke" trail behind the bullet or a puff of grey at 30 -50 yards where the bullet comes apart. The Speer 52 gr HP out of a 7" twist AR at 3200 fps will many times make a "banana peel" hole through a 25 yard target and won't make it to a 100 yard target.

This has nothing to do with the RPM threshold as such. It has to do with the centrifugal force over coming the structural integrety of the very thin jackets and soft lead cores.

Larry Gibson

[geargnasher]

Gear

I’m going to suggest you research rate of spin as it relates to bullets. You will find that the rate of spin of bullet deteriorates very little as range increases and velocity drops. That is a fact. No kidding. I learned that in high-school physics. It was never a point of contention for me. A thrown football, regardless of the quarterback, comes no where near the RPM we are talking about. Not a good analogy at all. It's a perfect analogy. A boolit isn't as big as a football, nor carries most of it's mass on the outside like a football does, but they are rotating aerodynamic bodies in flight, and subject to the same forces. Ever see the slow-motion shot from behind the Qback as he zings a Hail Mary pass? Notice the helical path the football makes due to the mass of the laces? Notice how small the helix is?As I explained to 44man, a bullet “going to sleep” is a different aspect of ballistics and not the same as the RPM threshold, apples and oranges. I never said it was, where are you coming up with that? The only mention had to do with a thrown football, after a couple of revs it stabilizes from the launch embalance of the passer's hand.

BTW; the bullet will make more turns in the donkey but the RPM of the bullet remains the same. Glad we agree on something. Spin a top on a small stool. Now quickly lift the stool 6 feet. Does the RPM of the top increase? Now low the stool very quickly. Does the RPM decrease? It does neither because the RPM of the top will remain relatively constant whether the top is moving in either direction. You correctly answer your own argument here with “a rate of 4,000 rotations in 3,000 feet at the muzzle is now traveling at a rate of 4,000 rotations in 2,000 feet”. The bullet is making the same 4000 revolutions (that’s the same RPM) regardless of the distance. You really do need to read up on this in a good ballistics book or manual. Larry, what's the matter with you? You're the one arguing that I'm mistaken about it, now you use my own and correct example and tell ME that I need to study ballistics more? I NEVER argued that a boolit maintains virtually the same RPM from muzzle to target, I was trying to point out that a boolit won't make the same number of turns through a given distance downrange as it would at the muzzle, and you and Tatume both told me I was wrong.

You’re reading more into the tire analogy than is there. Jack the car up and spin the tires free of road surface and the same thing I described will happen.

An equation? So why then can’t you or DrB come up with an equation that will tell us the exact velocity at which a .308W with a 150 gr bullet will get the best accuracy? You can't. Now you're getting my drift. You can't either. Know why? Because it ain't the RPM that's causing the problem. If it were, it would be a very simple problem to solve, and DrB and I both are familiar with the math it takes to calculate the effect of dymamic embalance of a rotating object and the effect upon the orbit of the projectile about an imaginary, or inertially neutral, geometric center.Once again you, like DrB, want an exact RPM figure or a way to figure exactly at what RPM the threshold will be reached and will happen. As with an equation to tell us exactly at what fps accuracy will occur, it doesn’t work that way. Then what merit does you theory even have as far as a loading consideration goes? It is no more useful than Richard Lee's theory of ONLY considering alloy strength when loading cast boolits. Don't get me wrong, his method has worked and yielded satisfactory accuracy every time I've followed it, but it is very limiting performance-wise and isn't the gospel on what CAN work, only on what almost always DOES work. I find it VERY interesting that any given rifle load I've looked up or tested using Lee's load data and my chronograph seems to have the same accuracy limits as your RPM theory. You say it's the rotational embalance, he says it's the strength limit of the alloy. Two theories, both explain the same threshold limit, neither one really accounts for what's going on or how to overcome it, although at least his theory follows a fairly simple math formula that holds water in practice.I have already explained that the reason is the variables. That's right. You have to consider the big picture, don't you? Lots more to it than RPM, much of it not well understood.

But once again; we can assume with a regular cast bullet with a BHN of 15 -18 in a medium capacity case using a medium burning powder that the bullet will reach the RPM threshold between 120,000 – 140,000 RPM. That is based on my 45+ years of shooting such and 45+ years of observing the same with other shooters. Many here like felix also agree. No equation, no way to determine the exact RPM when that set of components in that particular rifle under the conditions tested comes up to the threshold other than to test it. Fair enough. So what CAUSES this limit? Is it the one thing, RPM, or is it a combination of the multitude of variables?

Again; the helix is not my theory. The helix is a ballistic fact. Yes it is fact. Watch a football game. If you would research it in a ballistics book or manual you will find that out. I never discounted that, only the AMOUNT you claim it affects group dispersion above a certain RPM point. I suggest Understanding Modern Ballistics by Robert A. Rinker for those just beginning a study of ballistics. A better understanding of ballistics might enhance the credibility of your statements. You have yet to refute or even answer any of the questions I have yet posed, so how is my lack of education involving ballistics (which is nothing more than applied physics, of which I have a formal education, my degree is in mechanical engineering, we touched on applications of physics a time or two) relevant to the questions I've asked? You understand it better than I do. Are not my questions legitimate?

In the above post to you I explained that the helical spiral may take a long distance to even make a significant arc around the flight path. I also explained that it may not spiral but may simply go off on a tangent (the “blown group” you refer to. BS. orbiting bodies don't just "go off on a tangent line" unless something seriously changes, like a rock thrown from a spinning sling or gravel from a tire tread, which is a little different from boolits anyway because of the perpendicular direction of force to the rotating axis. A spinning boolit has a gyroscopic effect acting on it, and while it will shed a pp or grease from the grooves by force, it won't suddenly depart from it's flight path unless encountering some force far greater than it's stabilizing inertial forces, like deflecting off of water or steel, or air. Besides, a boolit can go sideways through a target and still hit in the group, and do so with regularity. I disagree very much with the significance of air pressure acting on the boolit to make shots go severely wide. The air brings up another point so often misunderstood. A puff of wind doesn't push a boolit off course. The wind moves the entire column of media through which the boolit travels, taking the boolit with it. Like a fly buzzing around in you car while you're going down the highway: The fly isn't flying 70 MPH, he's just buzzing through the air INSIDE the car, which is moving relative to the outside air. Many here have pushed cast bullets to the point they don’t even print on target anymore because the group is so large. I've seen it, and under all sorts of velocities and conditions. I've also witnessed it one time from the spotting scope, and the boolit just flew out the muzzle on a wide line, the shooter was a very experienced J-word benchrester and he had no explanation for the flier, in fact said the sight picture was the same through recoil as the other shots. The definition I posted in quotations and italics in this thread in above posts and the other thread explain it quite well and is a direct quote from a ballistics manual. It is not my theory; again should you bother to research it you would find out. “Donut patterns”; what is the “distance to the target” are you talking about? Just how many helical spirals do you perceive happen between muzzle and 100 yards, or 200 yards? Not sure. Could be thousands if you're talking about the little, first-order wobbles caused by boolit balance problems every rotation of the boolit, or maybe several across the distance if you're talking multi-order vibrations. The helical spiral may take several hundred yards if not more to be noticeable (probably why those who say they haven’t seen it haven’t seen it), it may take far more range than that and as explained it may not make a complete spiral to the maximum range of the bullet. Ok, there you go Larry. Now you understand why I don't believe your RPM theory. You said "Above that the RPM threshold is when the centrifugal force becomes strong enough that the bullet begins to follow a helical path outwardly from the line of departure or intended path. The “diameter of the path” is dependant on the centrifugal force (the higher the RPM over the threshold the higher the centrifugal force and the larger the diameter of the helical spiral will be) and the range at which measured. It is not a constant diameter but increases as the range increases. This is the why/where the non linear expansion of the groups comes from and why it is more pronounced at longer ranges past 100 yards." Well, if the helix is several hundred yards long it will affect the point of impact, but not the group size. Or if it does affect group size, it will print a doughnut, not a random scatter. I don't see doughnuts on my 200 -yard targets at speeds where the groups blow up, I see random scatter, as many in the ten ring as anywhere else. As already explained; it depends. By “donut” patterns” you have perceived something happening that I have not said does and, in fact, explained doesn’t. No, there will not be “donut patterns” on the target at any reasonable range we shoot cast bullets at and I’ve never indicated there would be “one or two spirals of the helix between muzzle and target”. You perceive that apparently and your perception is not correct. Perhaps my perception is incorrect. But based upon what you said that I quoted above, I don't see how there could be any other conclusion. If the boolit begins to follow a growing spiral path due to RPM exceeding the balance limit of the boolit, then the boolits would print in a ring, unless there were some that were perfect and hit in the center of the group like they're supposed to, and some that are only slightly imperfect, so print in between the fliers and the perfect ones, making an even dispersion. What I HAVE observed is boolits flying either fairly straight into a good group, or flying fairly straight into a large group, and flying wildly from the start, so you're right, and I am one who just hasn't observed a predictable spiral being the result of blown groups by boolits exceeding the RPM threshold.

I’m sure Pwdawg or others on the PP forum can satisfy you needs for pictures. However, why don’t you test them and find out for yourself rather than hypothesis how it can't be? I have already explained on this thread and others the difference between a PP’d cast bullet and a naked one. Pwdawg is probably the most experienced here at shooting PP’d cast bullets at HV and he has also told you the difference on this thread. You are free to believe what you will but the facts supporting the differences are readily apparent. No, there aren't any facts about reasons WHY the PP blows your RPM theory out the window. Suppositions, yes. Lots of results that prove PP works wonders, yes. No facts that explain exactly why a PP makes a regular boolit immune to the effects of centrifugal unbalancing forces or whatever you think makes the groups blow at the same speeds with unpatched boolits.

“Here's a good test of the theory. Take jacketed bullets and deform them, either by bending the noses slightly, or by drilling small holes in the side of the jacket to create an unbalanced condition. Then observe the RPM limits and patterns on the targets of THOSE. If the theory is true, similar limits should be observed as we commonly note with cast boolits. They should shoot accurately to 120k-140K rpm, then go to hell suddenly, just like cast. If the group dispersion is more linear with regard to rpm increase, then we can assume that there is something else going on with cast than just the effects of imperfections showing up catastrophically at a certain RPM.?"


I already ran that test for Bass Ackwards several years back. I used M118SB ammunition in a 10” twist .308W rifle. I shot 10 shot groups at 50 yards, 100 yards and 200 yards with unmodified bullets. I then drilled on .3 gr of the bullet out on the side of 30 more rounds. I then fired the same 10 shot groups at 50, 100 and 200 yards. The expansion of the regular unaltered M118SB was predictable and linear between all ranges. The non linear group expansion of the altered M118SB was also predictable; a small difference between 50 and 100 yards and a large non linear expansion between 100 and 200 yards. Excellent. Now that makes sense. I missed that test. The same things that happen to cast boolits exceeding the RPM threshold happen to Jwords, can I can assume you shot goth sets at the same RPM and that RPM was above the threshold for equivalent cast boolits in that gun? If so that seems pretty conclusive to me, only it's still a stretch to assume that it's launch damage causing the threshold, for powder burn rate can be tweaked all around, boolit fit can be changed drastically, and still the same RPM/accuracy threshold exists for that gun. The question now is HOW are the boolits becoming unbalanced and what can we do to prevent it, or is it muzzle exit problems or something else entirely? I see your observations that the threshold exists and that imbalance can explain it, but it seems simple enough that removing or extending the balance limit would increase the RPM limit, and for some reason it's very difficult to do so at a certain point. Is this point the resonant imbalance of your tire analogy? If the RPM threshold is merely a balance limit, it would stand to reason that one merely has to load beyond that limit a bit to smooth things out a bit, just like "driving through" a vibration point with a bad tire, the vibration point, or point where the imbalance makes a noticeable difference, is very narrow, and calms down on the other side of it. Seems that if the RPM threshold was due strictly to a balance issue, it would just be a bump in the RPM spectrum, but that's where my knowledge of external ballistics reaches it's threshold, and the forces acting on the boolit are more complex than on a tire.

I also, as reported to DrB on his thread, conducted basically the same experiment using the 311291 in an ’06 one load was below the RPM threshold at 1912 fps (136,400 RPM). The 10 shot groups with that load at 50, 100 and 200 yards were .7”, 1.3” and 2.5” restively. That is quite normal linear expansion. The next load was the same bullet loaded over the RPM threshold at 2500+ fps (179,400 RPM). The groups at 50, 100 and 200 yards were 2.55”, 4.7” and 14.5” respectively. What we see there is little non linear expansion between 50 and 100 yards but a very large non linear group expansion of 14.5” at 200 yards. I have run similar test so many times with a variety of cartridges and twists over the years. The results are the same; exceed the RPM threshold and groups open in a non linear fashion as range increases. I know that years of observation of facts is why you developed your theory, but you know that if you added a patch to that boolit you could shoot the same groups you got at 1900 fps at least 2600 fps, or whereever your safe pressure limit was for the gun and load combo, and I can't figure out how the paper makes the boolit that much more perfect in flight, as it would have to be for those results according to your theory.

If you would care to conduct your own tests in an attempt to prove your own thesis/theory correct then feel free to do so and report back your findings. Better than using a jacketed bullet why don’t you do the same test with a cast bullet? That would be more relevant here as we are discussing the RPM threshold as it relates to cast bullets. As to jacketed bullets I suggest you read any one of the later Hornady loading manuals (try page 29 of the current, 8th Edition Horandy manual). Again, not my “theory” here but quoting directly from the ballisticians at Hornady;

“ As long as the bullet is in the barrel it rotates around its center of form but when it leaves the barrel it spins around its center of gravity and this causes it to veer slightly off its intended course at a tangent to the spiral described by its center of gravity as it went up the bore.” No kidding. The question is how much.

Sound familiar, like what I stated/quoted and have been saying all along? Gear, you may be smarter than me, DrB may be smarter than me and some others here, but do you think you or any of them are smarter than the ballisticians at Hornady who have put that out in millions of reloading manuals? Again, it’s not my “theory”, it is ballistics. So, by the laws of balllistics, and by your own theory, all a person has to do is cast a perfect boolit and launch it without damaging it and it will shoot as well at the same velocities as jacketed bullets? How come, by your own admission, it's virtually impossible to do so above the soul-killing and all-encompassing RPM threshold? If imbalance was the only factor, or even the most important factor to this limit, it seems that it would easily be overcome by careful casting, culling, and loading techniques, and would show up gradually, not like a brick-wall barrier at a certain point in the RPM range. But it doesn't seem to be that way, that's why I keep throwing things out there trying to get to the bottom of this, hoping you can educate me a little bit on why this limit occurs, and what can be done about it.

I have conducted enough tests to prove the RPM threshold does exist, particularly with cast bullets, and what happens when it is exceeded. No, I think you've proven that there is a limit to practical accuracy of plain cast boolits at a reasonably common point, but I don't think you have shown any proof that the failure is because it's just spinning too fast. You've shown a fairly close relationship between RPM and group dispersion, but never really proven what happens to cause it. Yes, you've proven that an unbalanced boolit/bullet CAN cause it, but not why the inverse isn't really true, that a near-perfect boolit would be immune to this threshold, same as a good jacketed bullet. I suggest you conduct some of your own test then study up on ballistics before hypothesizing erroneously.

Larry Gibson

Here's my five characters.....

Gear

[geargnasher]

Onesonek

"Larry thinks the paper protects the boolit well enough during launch to account for the great increase in RPM potential, and it might, but what about outside the gun?"

Consider that the PP does protect the cast bullet, thus there is less unwanted imbalance done to the cast bullet during acceleration (launch). The less unbalanced the bullet is (or the more balanced the cast bullet is) The less the centrifugal force of higher RPM has to act upon and the bullet is more accurate at higher velocity. Basicly simple in that the PP protects and supports the cast bullet preventing obturation, setback, sloughing, etc. to a much higher velcoity. Very straightforward line of reasoning, Larry. Where it breaks down is in the instance of a boolit only patched on the driving bands. Same nose, only it doesn't have any ill effect when the bands are patched. That tells me that nose slump has nothing to do with the imbalance that you say is the cause of the RPM threshold. Maybe it's some other part of the boolit that gets protected by the patch, a part that is more critical to the external ballistic performance of the boolit. May not be able to convince gear of that but him not being convinced does not make it a proven fact. Of course not. All I ask is that you make fewer logical leaps between your observations and your conclusions. Perhaps he has some scientific reason why pwdawg can shoot the 311284 PP'd at 3000 fps with excellent accuracy but he nor any one else can/is shooting the same 311284 naked at 3000 fps with equal accuracy? Ya, Larry, I was asking YOU to explain it to ME, because the RPM explanation doesn't hold water in that case. I don't have any theories, but yours don't totally or explain with any satisfaction the factor either, and the whole point of my posts regarding this is to get you to explain why some of these discrepencies exist. I figured you'd have enough experience to know, I know I sure don't. You talk about setback, slumping, etc. being prevented by PP and thus raising the RPM threshold over 30% by enabling the launch of a more perfect boolit, but how does the patch prevent the nose from slumping unevenly in the bore any more than an unpatched boolit, when in some cases the nose of the patched boolit isn't even patched? I don't follow that line of reasoning, and I'm convinced there is some other factor responsible for this "threshold" of accuracy performance.

Larry Gibson

Just looking for a few answers to things opposing your theory, still haven't gotten them.

Gear

[Bret4207]

No, Bret, it's going faster. Now before you get freaked out by that, understand that it's all relative to time.

Take a trip with me on the back of a boolit, using some made-up but realistic numbers: You're drilling cull burros with a 220 Swift. Your muzzle velocity is 3000 fps, the twist is one in nine. The burro is two feet across. If you shot the burro point-blank at 3000 fps, the bullet would make 2-2/3 revolutions through the burro. Farther down range, your impact velocity is 2000 fps at, say 300 yards, but the rotational velocity is still a function of time, and is still turning practically the same amount of RPM, only velocity (distance traveled in a given time period) is LESS. Therefore, at 2000 fps, the boolit that was traveling at a rate of 4,000 rotations in 3,000 feet at the muzzle is now traveling at a rate of 4,000 rotations in 2,000 feet, and will be making one rotation in SIX INCHES instead of one rotation in NINE INCHES that it was at the muzzle. When the bullet passes through the burro, it will make four revolutions going through instead of the 2-2/3 it would have made at point-blank.

I don't know why this is such a difficult thing to get. Because math and me don't see eye to eye! If the barrel went all the way to a 300-yard target with the same twist the whole way, the boolit would have to be going the same forward velocity at the target as it was at the "muzzle" to make the same number of rotations in a given time period. In other words, for the boolit to be maintaining it's same rate of spin at the target that it does at the muzzle (which it essentially does), yet lose velocity (which it most certainly does, and a significant amount), the number of turns traced in a given amount of travel must increase.

Here's another analogy: A propeller on a small aircraft. Sitting on the runway with the brakes set and ready for launch, the prop is wound up tight at takeoff RPM, then the brakes are released and it begins to accelerate forward, maintaining the same RPM as the plane continues to accelerate down the runway. From the plane's perspective, the prop is turning the same speed the whole time, but if there were oil dripping off the prop blades as it went from a standstill to takeoff, the dripmarks on the runway would go from a puddle at standstill to ever-increasing sling marks, and at 150 mph the marks would be much more widely spaced than at 10 feet after launch.

If that doesn't click, how about this: oil is dripping at a constant rate from a leaky pan plug on you car 'cause the lube monkey you took it to for an oil change didn't replace the cracked Nylon gasket. The drip marks on the ground will be closer to each other at 5 mph than they will be at 55 mph. Agree? Of course they will be. The drip was a constant, the forward velocity was not. Same with boolits spinning in the air. If each rotation of a boolit was an oil drip, the drips will be closer together the slower the boolit goes, and as the boolit decelerates downrange, the boolit will be making more revolutions in a given distance, even though it's revolving at virtually the same rate (like the constant oil drip) as it was at launch.

The problem seems to be that some people have the concept that because twist rate and boolit rotation is fixed, it will be so along the entire boolit's path, just like tires on a car in contact with the road. Not the same thing. Here's what you're probably thinking: A tire will rotate at different speeds as the road speed changes, they are fixed to each other. As the car slows, so does the tire, and it doesn't matter if you go a mile at 100 MPH or a mile at one MPH, the tire will make the same number of revolutions. This is not the same thing as the oil drip or boolit in flight. Notice that if the tire makes a mile at one mile per hour, it is turning SLOWWWWW. If it makes the same mile in the same number of revolutions, but at 100 miles an hour, it is turning FAST. A boolit is rotating at the same rate whether going forward at 3000 fps or one fps, but the number of rotations it makes in a foot is much less in 3000 feet than of travel than it is in one foot of travel.

Gear

I think I understand what you're saying, that the starting twist remains relatively constant and that the speed changes making the twist relatively faster. It still seems like a lot of other mathematically provable points that are real hard to prove in actual practice. Too bad we don't have a way to show this in simple pictures for non-math believers like me.

Thanks for the explanation. Skeptically yours, Bret:wink:

[44man]

44man, how far was the paper target? Did you do any tests to determine at what distance the boolit came apart? And how far it was effective in crow after it had come apart?

That supports 44man's account of the S&W 29 and the 30-30 TC.
I was just shooting 100 yards with the .220 Swift. That drove me nuts all the time because the old Winchester pre 64 had a 1 in 10 twist and loved the 60 gr Hornady. I could never shoot less then 1" at 100. It was over spun at the velocity I shot. It had to be shooting a helix. I sighted this gun at 350 yards and never shot at chucks under 200, I would actually walk away from them another 200 yards to get at least 400.
One day while sighting in I put 5 shots in 1/4" at 350 yards but it would NOT shoot at 100. There could only be one explanation! The RPM's did not change much but velocity dropped, the helix went away, the bullet went to sleep.
This was the reason I loved the .220 over the 22-250, a faster twist for the heavy bullet for better long range results. The .222, .223 and 22-250 shot better at close range with the slower twists.
Now the 29, The helix was VERY FAST around the flight path like touching a gyroscope. As it went downrange, it got less fast until I would lose sight of the bullet so I suspect at some range the bullet would go to sleep. It is strange that 10 gr more bullet weight eliminated the helix. It was not seen from the Ruger at all even with a 240 gr.
You can see what close range BR shooters do, they use a slower twist to eliminate the helix but want a faster twist for long range.
I do not know what causes the corkscrew around the flight path but there is some relationship to velocity, not out of balance bullets.
The question is, what stops the helix? Why do bullets go to sleep? Do the RPM's actually slow just enough? What is the relationship to velocity?
I don't like math or theory, I go by experience in all that I have seen. I would never try to explain the what and why of it.
Regardless, the stopping of the helix is the point of the bullet going to sleep. Whether out of the muzzle or at some point down range.
This stuff turns into the 1000# of canaries in a plane and does the plane lose weight if they all fly. :kidding:
My way works. Increase velocity until groups close. Keep increasing velocity until groups start to open then back down to the best spot. To keep increasing velocity after passing the correct spot will only tell you that bullet will not shoot there. Calling it an RPM threshold or any other name is a waste of time. Nothing you ever do will make the bullet shoot out of it's accuracy point.
To have a boolit shoot super at 1500 fps and take it to 3200 fps expecting it to shoot is just folly. To try and explain it is worse. The gun you have and the rate of twist will dictate what you can do.
The best illustration is the guy that buys a revolver and looks for the highest velocity possible, then takes the same boolit and wants to shoot it dead slow. The gun has a twist rate built in, it works best where it works but handgun shooters forget twist.
Take your .454 and shoot it at 1600 fps and then want the same boolit to shoot at 800 fps is very stupid. Get a different boolit.

[Junior1942]

Point: the paper patch received most of the rifling indentations, not the bullet surface. The bullet left the muzzle much less deformed than a normal bullet.

Point: dud artillery shells have been observed still spinning in the cavity they punched in the ground. That's zero velocity with RPMs.

Point: my Q effect. Only one thing could cause it: the bullet throwing off part of the area between lube grooves due to an RPM value higher than the bullet can take. Picture a #. In the # you can see both semi-vertical land marks/indentations and horizontal lube groove indentations. The comma on a bullet hole was caused by the little leaning box in the # detaching itself from the bullet on one side. That comma is the first sign of bullet damage due to too-high RPMs for the bullet's alloy and construction.

All jacketed and cast bullets have an RPM threshold past which they will self-destruct.

[357shooter]

Not sure why the RPM vs FPS connection is such a big topic. There is no connection, but I guess that's just me.

It seems to me the air pressure on the bullet nose, which is magnified by longer bullets, plays a much bigger role in destabilizing a bullet. If i understand it correctly the air pressure by increased velocity is offset by the higher RPM (when it left the barrel, and a direct result of the twist rate) of the higher velocity.

Bullet length and RPM need to be balanced so it will "sleep" at some point. Velocity is a third element, but down the list and allows fine tuning for accuracy. It gets discussed most often because it's the easiest to tune.

[geargnasher]

Not sure why the RPM vs FPS connection is such a big topic. There is no connection, but I guess that's just me. The relationship is direct: RPM of a boolit is directly related to twist rate and forward velocity. Not sure what you meant.

It seems to me the air pressure on the bullet nose, which is magnified by longer bullets, plays a much bigger role in destabilizing a bullet. If i understand it correctly the air pressure by increased velocity is offset by the higher RPM (when it left the barrel, and a direct result of the twist rate) of the higher velocity. Lots of things going on with that. Air pressure on the nose, particularly uneven pressure due to a nose deformation, might cause a boolit to yaw, but the air pressure will apply to the side of the boolit's base with a large amount of pressure, too, since the boolit will yaw about it's fore-and-aft center of gravity. these pressures sometimes balance themselves out in a yaw condition, explaining why one or more keyholes can appear within the dispersion of a normal group, and also why keyholes can be wild fliers depending on (I think) boolit shape and the drag profile it presents when yawing through the air. I suppose that a boolit rotating faster due to higher velocity will be "more" stable and resist deflection more, but you have to remember that the boolit is still spinning, and any defect on the nose is imparting equal outward forces on the air pressure as the boolit rotates.

Bullet length and RPM need to be balanced so it will "sleep" at some point. Velocity is a third element, but down the list and allows fine tuning for accuracy. It gets discussed most often because it's the easiest to tune.

This begs another question: Somebody schooled in long-range techical ballistics please explain what "going to sleep" really is. Is it a point where, as forward velocity decreases, but rotational velocity remains virtually the same, that the boolit becomes relatively MORE stablized by spinning more turns in a given distance, and so eliminates the helical path it had been following? If the Helix, like Larry suggests, gets larger at a non-linear rate above the RPM threshold, isn't it reasonable to assume that it will get smaller, or taper DOWN at a certain distance WITHIN the rpm threshold?

Gear

[Larry Gibson]

onesonek

"But I don't understand how the high rpms are creating a balance problem in flight......"

The higher RPM do not create a balance problem in flight. The centrifugal force of the higher RPMs have a greater affect on the imbalances of the bullet. The faster we accellerate a cast bullet in the barrel the higher the probability of unwanted obturation, setback, sloughing, etc.. If the bullet leaves the barrel balanced then the centrifugal force radiates equally in all directions. If the bullet is unbalanced with more weight on one side of the center of form then the centrifugal force will act more in that direction. At a certain point of increased RPM the centrifugal force becomes great enough to cause the bullet to go off on a tangent and begin the helical spiral. That is the the RPM threshold.

The PP is a jacket and does protect the cast bullet from that unwanted obturation, setback, sloughing, etc. as the bullet accellerates in the bore to a much higher velocity. Thus the PP'd cast bullet is leaving the muzzle in a much better ballance condition than the naked cast bullet at any given velocity. The PP coming off the bullet on muzzle exit has nothing to do with whether imbalances were done to the bullet in the bore during acceleration. Point is; the PP protects the cast bullet during accleration from imbalaces being done to it while in the bore. The PP's cast bullet leaves the bore in a more balanced condition than a naked cast bullet given the same velocity. Ergo, since the PP'd bullet is more balanced it will be more accurate above the RPM threshold of the naked cast bullet.

"Cast is not cast?"

No, not all "cast" bullets are the same. Wrap a PP around a cast bullet or a metal jacket (Speer "casts" the cores in the jackets in the Hot Core line) and the "cast' bullet becomes better protected during accleration and will maintain balance to a much higher velocity level than will a naked cast bullet.

"I guess what I'm saying is, I'm lost. As at first, your arguements for the threshold has some reasonable rationale behind them. But the PP boolit, logically removed the rationale for me, as both boolits are naked in flight."

Simply understand the damage (imbalancing) is done during acceleration in the bore not during flight. During flight is where the adverse affect on the bullet takes place that causes inaccuracy.

Larry Gibson

[Larry Gibson]

Back in 1988 I brought a new Colt H-bar. Had 7:1 twist. Shooting 55grain UMc brand it could not hit anything. I assumed at the time the twist rate made the bullet come apart. As most AR's of the time used 1:12 twist.

I wonder why they came out with the fast twist AR's to use with heavier bullets?

The SAW was also a 5.56 and one of the requirements was to have tracer burn to 600 meters. The 5.56 tracer is a very long bullet and required the faster twist to stabilize it. That's why the 7" twist. The standard M855 (62 gr FMJBT) is adequately stabitlized in a 9" - 10" though. Most M193 (55 gr FMJBT) do quite well in 9 - 10" twists also. There have been problems with some M193 in 7" twist barrels though. That was with the longer 'A2s 20" barrels. with the current shorter barrels of the M4 series the velocity/RPM is lowered so much it's not a problem. Lethality has become the problem.

Larry Gibson

[Larry Gibson]

"This has nothing to do with the RPM threshold as such. It has to do with the centrifugal force over coming the structural integrety of the very thin jackets and soft lead cores."



I know it's off the topic in relation to cast Larry,,,,,, but.
It is the centrifugal force, that in essence ruins the bullets integrity, caused by running past the rpm threshold of the bullet design So in that sense, they are directly related? Looking at what you noted with 2 different faster twist rates at lower velocity, compared to what I seen with slower twist at higher velocity,,, it seems logical.
As for the cast rpm threshold issue at hand, I haven't the experience to comment, so I'm just reading at this point.

Two different issues; bullets coming apart in flight has to do with the structural strength of the bullet. The RPM threshold has to do with how incresing centrifugal force acts upon imbalances causing inaccuracy. While the centrafugal force is a common denomonater with both the two are not the same. Same as a wind will blow a bullet off and the same wind will cool you down. Same wind, two different things.

Larry Gibson

[geargnasher]

onesonek

"But I don't understand how the high rpms are creating a balance problem in flight......"

The higher RPM do not create a balance problem in flight. The centrifugal force of the higher RPMs have a greater affect on the imbalances of the bullet. The faster we accellerate a cast bullet in the barrel the higher the probability of unwanted obturation, setback, sloughing, etc.. If the bullet leaves the barrel balanced then the centrifugal force radiates equally in all directions. If the bullet is unbalanced with more weight on one side of the center of form then the centrifugal force will act more in that direction. At a certain point of increased RPM the centrifugal force becomes great enough to cause the bullet to go off on a tangent and begin the helical spiral. That is the the RPM threshold.

The PP is a jacket and does protect the cast bullet from that unwanted obturation, setback, sloughing, etc. as the bullet accellerates in the bore to a much higher velocity. If this were a Wikipedia entry there would be red flags all over the place saying "DOCUMENTATION NEEDED". Thus the PP'd cast bullet is leaving the muzzle in a much better ballance condition than the naked cast bullet at any given velocity. The PP coming off the bullet on muzzle exit has nothing to do with whether imbalances were done to the bullet in the bore during acceleration. Point is; the PP protects the cast bullet during accleration from imbalaces being done to it while in the bore. The PP's cast bullet leaves the bore in a more balanced condition than a naked cast bullet given the same velocity. Ergo, since the PP'd bullet is more balanced it will be more accurate above the RPM threshold of the naked cast bullet. Well explained as usual, but still too many unsupported statements of "fact" that don't add up for me. You still haven't touched on how a half-patched boolit can shoot as well a a jacketed one when the same boolit, UN-patched, won't shoot nearly the same velocity. I don't buy the nose deformation/resulting imbalance thing causing the rpm threshold at all because of this simple fact.

"Cast is not cast?"

No, not all "cast" bullets are the same. Wrap a PP around a cast bullet or a metal jacket (Speer "casts" the cores in the jackets in the Hot Core line) and the "cast' bullet becomes better protected during accleration and will maintain balance to a much higher velocity level than will a naked cast bullet. Sounds good, but a copper jacket supports the unsupported nose core (to a point) better than paper can, even if you wrapped paper clear over the nose and twisted it to a point, yet patching the bands seems to extend the useful velocity range of a boolit to nearly the same as a copper jacketed one. Why?

"I guess what I'm saying is, I'm lost. As at first, your arguements for the threshold has some reasonable rationale behind them. But the PP boolit, logically removed the rationale for me, as both boolits are naked in flight."

Simply understand the damage (imbalancing) is done during acceleration in the bore not during flight. During flight is where the adverse affect on the bullet takes place that causes inaccuracy. Crystal-clear explanation of the idea. I don't think Onesonoak or I have any difficulty following your explanations, but I for one am skeptical that the paper patch is that good at preventing the sort of deformation you say is responsible for the increase in threshold. Now do I have an alternate explanation? I wish I did. Maybe someone does, but I don't think preventing off-center nose slumping is a principle cause of the threshold increase offered by the paper patch.

Larry Gibson

Onesonoak, I know that was addressed to you, but I'm responding in general to Larry's statements, not meaing to step on anyone's toes here. Forgive me if I have.

Gear

[Larry Gibson]

Gear

obviously you've made up your mind without any testing of your own. Instead of Hypothosizing why don't you conduct some tests of your own?

In all your hypothosizing you have asked one good question regarding PP'd bullets. This is not a thread about shooting PP'd bullets BTW. It is about the RPM threshold on naked cast bullets. Keep that in mind will you? I will answer your question though;

"You talk about setback, slumping, etc. being prevented by PP and thus raising the RPM threshold over 30% by enabling the launch of a more perfect boolit, but how does the patch prevent the nose from slumping unevenly in the bore any more than an unpatched boolit, when in some cases the nose of the patched boolit isn't even patched?"

Have you ever seen pictures (there is one in the NRA Cast Bullet Handbook) or looked closely at recover cast rifle bullets, especially those with long bore riding noses, and seen rifling marks on one side of the nose? If so you will also note that the nose os not bent but has basicly tilted to the side. Also if you look closely you will see the nose tilted because the lube grooves collapsed under that prtion of the tilt. When lube grooves collapse it can be partially on only one portion of the circumference. It is not an even collapse allthe way around. This can be especially the case in WQ'd bullets where there are spots in the bullet that are harder than other spots.

If the lube grooves collapse on on side of the bullet the can and does tilt in that direction. The PP supports the driving bands and lube grooves and keeps them from collapsing to much greater degree thatn the unsupported lube grooves of the naked cast bullet. That's why.

Larry Gibson

[Larry Gibson]

This begs another question: Somebody schooled in long-range techical ballistics please explain what "going to sleep" really is. Is it a point where, as forward velocity decreases, but rotational velocity remains virtually the same, that the boolit becomes relatively MORE stablized by spinning more turns in a given distance, and so eliminates the helical path it had been following? If the Helix, like Larry suggests, gets larger at a non-linear rate above the RPM threshold, isn't it reasonable to assume that it will get smaller, or taper DOWN at a certain distance WITHIN the rpm threshold?

Gear

Perhaps if you would read a ballistics book (I've already recommended a very good beginning one to you) you'd understand. With rifles that exhibit the "going to sleep" phenomanon, such as 44mans, the cause is yaw and precessions. To quote from the book I suggest you read;

"The initial yaw as the bullet leaves the muzzle is governed mostly by stability (44man's was a fast 10" twist). The direction of yaw is haphazard or random and can be anywhere aroind the 360 degrees of the muzzle. This makes target dispersion larger in cases of considerable yaw with low stability (in 44man's case the bullet was over stabilized).......The yaw may be extremely high with the use of poor and mis-matched equipment (a 10" twist for the Swift which normally has a 14" twist). The force on the bullet is not on the center of gravity but on the front of it. the bullet is trying to tumble in flight. The initial wobble that is yaw and precesion can last up to 200+ yards before settling down."

This yaw and precession and the bullet going to sleep has nothing to do with the RPM threshold, it is a completely different action. Basically with 44man's 220 Swift with the fast 10" twist the over stabilized bullets had yaw and were affected by precession on exit from the muzzle and it took a couple hundred yards for the rotaional stability to over come the yaw and precession and the bullets settled down or as is commonly refered to; "went to sleep".

Larry Gibson

[geargnasher]

Gear

obviously you've made up your mind without any testing of your own. I haven't made up my mind, but until I can get satisfactory and proven answers to some inconsistencies with your theory, I can't accept it as truth.Instead of Hypothosizing why don't you conduct some tests of your own? Much of my skepticism evolves from my own testing and observations, particularly recent experiments with HV PP.

In all your hypothosizing you have asked one good question regarding PP'd bullets. This is not a thread about shooting PP'd bullets BTW. It is about the RPM threshold on naked cast bullets. Keep that in mind will you? Don't try to squirrel out of this one, Larry, it won't work. Paper patching is a loading technique for shooting cast that alters the properties of the boolit, same as using filler, thicker case necks, slower powder, whatever. It is possible to shoot THE SAME boolit either patched or not, so it's interesting to discover the cause of why merely adding the patch has such a drastic effect upon your theory. I will answer your question though;

"You talk about setback, slumping, etc. being prevented by PP and thus raising the RPM threshold over 30% by enabling the launch of a more perfect boolit, but how does the patch prevent the nose from slumping unevenly in the bore any more than an unpatched boolit, when in some cases the nose of the patched boolit isn't even patched?"

Have you ever seen pictures (there is one in the NRA Cast Bullet Handbook) or looked closely at recover cast rifle bullets, especially those with long bore riding noses, and seen rifling marks on one side of the nose? If so you will also note that the nose os not bent but has basicly tilted to the side. Also if you look closely you will see the nose tilted because the lube grooves collapsed under that prtion of the tilt. When lube grooves collapse it can be partially on only one portion of the circumference. It is not an even collapse allthe way around. This can be especially the case in WQ'd bullets where there are spots in the bullet that are harder than other spots. I fully understand what nose slump is, no need for the elementary reiteration of it. I've seen pics, and I've noted it many times in my recovered boolits, particularly Keith-style revolver boolits that were launched at a rate where the static inertia of the nose exceeded the yield strength of the alloy. You still haven't even touched on how the paper patch, WHICH DOESN'T EVEN TOUCH THE OGIVE OF THE NOSE, can prevent this slump and increase the RPM threshold.

If the lube grooves collapse on on side of the bullet the can and does tilt in that direction. The PP supports the driving bands and lube grooves and keeps them from collapsing to much greater degree thatn the unsupported lube grooves of the naked cast bullet. You'll never convince me that paper can prevent the collapse of lube grooves. I can make a patched boolit accordion-up in my base-first sizer just as easily as an unpatched one. It's just paper, like wadding up the paper wrapper when sliding it off of a soda straw, it has very little strength in that dimension. That's why. No. Something else is going on. Some other factor that the PP affects which is not present in unpatched boolits, thus making the difference in accurate RPM/velocity potential. If it can be discovered, it might be applicable to plain cast boolits, and the RPM threshold eliminated or greatly extended.

Larry Gibson

Here are some of MY observations, food for thought in that there are a LOT of things acting to limit cast boolit accuracy/velocity performance, not just one thing called RPM. Plain-based, cast boolits have an accuracy/velocity threshold for some reason. It seems that .30 caliber PB boolits start to shoot bigger groups somewhere between 1400-1600 fps in ten-twist rifles, regardless of cartridge. They also start to lead the bore around 1500-1600 fps. Now add compacting filler, the leading can be eliminated to upwards of 2K fps pretty easily. Add a paper gas check without filler, the leading is also eliminated to at least 1800 fps in the one gun in which I tried it. Accuracy, however, had the same limits of around 1400-1600 fps. Add a copper gas check, accuracy is restored up to at least 2k fps in the same guns with the same alloy, add filler and it goes up a bit more, harden the alloy and accuracy/velocity potential goes up even more, and still more with slower powder. Scrap the gas check and use a paper jacket, the accuracy/velocity potential goes up at least by the same order as adding a copper check to a PB boolit. Difficult to say that it's merely boolit deformation inside the barrel during launch that's causing the external ballistic changes, I think it has to do more with barrel harmonics and muzzle exit, because if it was RPM/balance alone, that would be easier to eliminate with more perfect boolits, and HERE'S ANOTHER ONE, breech seating. Most of the guys that breech seat boolits use slow twist rates and comparatively low velocity. I tried breech-seating in .30-06 once, a few years back when I was hell-bent to get over 2400 fps with a regular cast boolit while maintaining 1.5 MOA accuracy. The guy who was doing my case prep for me (because I didn't have the tools) suggested it and even turned a seater on his lathe. I found it made no real difference, even after many tweaks to the load to compensate for the different dynamics of the case volume. while in no way conclusive, my thoughts on this experience were that boolit deformation on launch wasn't what I was battling at that point, my brass and boolit had been tweaked to fit my gun so well by that point that there was something else going on. Ultimately I never achieved the 1.5 MOA goal with any consistency much above 2400 fps, but I did get close, and could maintain 2 moa out to 2700, but change the temperature, time between shot strings (barrel heat), or the phase of the moon :smile: and it went south real quick. I wish I still had that tool, and wish the man that made it and helped me was still here, might do some more tests.

Gear

[Larry Gibson]

Gear

Let me suggest a simple test to you. Take your '06 (I assume it has the standard 10" twist?), a naked GC'd cast bullet of 170 - 200 gr cast of and alloy of 15 - 20 BHN, size and lube the bullet appropriately for your rifle and load in 1 gr increments using 4895 and a 1/2 - 3/4 gr dacron filler (you can load sans the filler but consistency will be better with the filler) from 25 gr to 35 gr. I suggest a minimum of 7 shot test strings with each powder charge but 5 shot strings will suffice for this test. Shoot them for group at 100 yards and chronograph them. Report back showing us the group sizes (scanned or pictures would be nice) and the average velocity for each charge. That will demonstrate whether there is an RPM threshold or not and where you find it with those componants in your rifle.

Try to test from a solid bench rest in relatively windless conditions to eliminate as much of shooter error and wind drft as possible. BTW; there are lots of .223s with twists from 7" upwards of 14' out there and also numerous .308Ws with twists from 10" to 14". You could borrow a couple of those with various twists and test them side by side and see if accuracy doesn't go south at a lower velocity in the faster twists.

Shouldn't be too hard for you to do an actual test of this to prove it one way or the other instead of just hypothesizing why the RPM threshold can't be. I have conducted test after test using just such different twist rifles proving the RPM threshold is real and valid with cast bullets. Why don't you conduct tests to prove to us your hypothesis that the RPM threshold can't be.

Larry Gibson

[357shooter]

The relationship is direct: RPM of a boolit is directly related to twist rate and forward velocity. Not sure what you meant.

GearIn the barrel that's true, as soon as the bullet exits the muzzle the RPM and velocity no longer have a cause and effect relationship. Without the rifling making the direct connection, there isn't any direct connection.

[Larry Gibson]

In the barrel that's true, as soon as the bullet exits the muzzle the RPM and velocity no longer have a cause and effect relationship. Without the rifling making the direct connection, there isn't any direct connection.

Very well put 357shooter.

Larry Gibson

[grouch]

Larry, I know you've been woking on this for a long time, but it seems to me more logical to consider "rim speed " than RPM because it should better relate to centrrfucal force than RPM does unless you limit your discussion to a single caliber.
Grouch

[geargnasher]

Larry, don't you read ANYTHING I say? I said from the beginning that I have observed the same thing happening as you have, but that I don't find the evidence that RPM is the absolute cause of it. Just like I don't find Richard Lee's pressure theory to be absolute either at HV.

If you want to see what I mean about observing the same things you have, check out this recent example, there have been many others over the years similar to it: I have been working with a brand-new, left-handed .30-06 I bought in 2006, on of the last ones made in New Haven. It's a *** really, rough everything and poor fit-finish. It is a one-in-ten, I checked with a tight patch. The bore is .301" and the groove is .309", the chamber neck is cut to almost .345" which makes fitting brass impossible, even with .311" boolits and military cases. I bought the Lee 312-185 mould to try this gun out, results I must say are typical. All these boolits were water-quenched 50/50 WW/roofing lead, having a month-old hardness of 19.3 bhn on the Lee scale. I started with Reloder 22 because it was the slowest, bulkiest powder I had on hand that would still burn decently at lower pressures. 4831 never worked well for me at lower pressures and 4350 was a bit fast for the velocity I wanted.





http://castboolits.gunloads.com/imagehosting/thum_89094e3ecec9af887.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=1723) This pic shows in the upper left target Reloader 22 at 45, 46, and 47 grains, the lower left shows it at 48, 49, and 50, the lower right shows it at 51 and 52. My order is top, LL, LR in the three dot targets, and top first/bottom last in the two dot targets. Notice how the groups here were best right around 48 grains, like the target on upper right where I tried 48 grains with and without BPI Original shot buffer. Velocities for the 48 grain load without filler were 2136, 2094, 2082, 2076, and 2139. Lots of ES, but most accurate by far. At 49 grains, where the load started to blow the groups, velocities were 2190, 2183, 2170, 2172, and 2186. Very small ES, very large group, fired after the 48-grain group under the same conditions, only a 10 minute barrel cooling break (standard for me).


http://castboolits.gunloads.com/imagehosting/thum_89094e3ecede054bd.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=1724) Here I tried 50 grains of RX22 with and without Dacron, don't know what happened there.

http://castboolits.gunloads.com/imagehosting/thum_89094e3eceb4525ec.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=1722) Here's a powder switch to H4350, one of my favorites. Top was 40 grains and 1/2 grain Dacron, forgot to write down two numbers but three of them were 2066, 2038, and 2071. Middle group was 39 grains and .7 Dacron, getting 1958, 2020, 2004, 2032, and 2083, the first three were overlapping in a beautiful triangle, the fourth was high, the fifth came back into the group somewhat. Same thing happened with the top group if you look carefully. I think barrel heat or too much lube (purge fliers) may be causing this. Then I took it to 41 grains, and as you would expect, blew the group. 2127, 2118, 2090, 2103, 2085. Anything over 2K fps starts to open up the groups with these two powders. That's about 144,000 RPM, what a shocker.

Now let me show you another real shocker: Richard Lee says that the reasonable accuracy limit for the strength of a 19.3 BHN alloy is 24, 703 PSI. Not having a PBL, I used my chronograph numbers to approximate pressures from his cast boolit load data, since the charge weights/velocity were off by a grain or two in my gun. Here's what I came up with: right about 47 grains of RX 22 gives somewhere around 23,000 PSI, and 48 close to 24,000, 49 exceeds his recommended allowance for loading just under the boolit strength, and guess what? Blown groups. Just like he predicted in his charts. Now look at the H4350, my chono data was within just a few FPS of the published data, really neat: Just like Lee's data, 39 grains was just over 2,000 fps average in my gun and pressure was 24,200, 41 grains that blew the group was 26,700 PSI and averaging around 2100 fps or 151,200 RPM, while the 40-grain load somewhere around 2050 fps was till holding together with some slight fliers at 25,400 PSI and 147,600 RPM.

So what does this mean? Just at the point that I exceeded the RPM theshold, accuracy deteriorated. Actually I pushed it a bit beyond where you say it usually is, but the boolit's a bit tougher than you said to use, too, so it adds up. The other thing, and this is my whole point, the Lee forumula was exceeded in exactly the same place you say the "RPM threshold" is reached, with the same effect on groups. Could it be that you're theory is the same as Mr. Lee's, but you call it something else? This is not the only time I've seen certain RPM and boolit strength coincide with accuracy deterioration, in fact every time I've measured velocity and strength and compared to Lee's charts, I get the same results with standard loading techniques, not doing anything fancy for case prep, boolit fit, or muzzle exit protection.

Go figure.

Gear

[geargnasher]

Larry, I know you've been woking on this for a long time, but it seems to me more logical to consider "rim speed " than RPM because it should better relate to centrrfucal force than RPM does unless you limit your discussion to a single caliber.
Grouch

I wasn't going to bring it up just yet, but since you did I might as well mention that there is, in fact, no such thing as "centrifugal" force. It's called a "ficticious force" because it's action on an object is totally different depending on which particular inertial reference frame the observer is placed.

Gear

[Larry Gibson]

I wasn't going to bring it up just yet, but since you did I might as well mention that there is, in fact, no such thing as "centrifugal" force. It's called a "ficticious force" because it's action on an object is totally different depending on which particular inertial reference frame the observer is placed.

Gear

Is that so? If it has an "action" then how can it be "fictiicious? Besides, you the shooter, are always in the same "inertial reference" as the "observer. If it is "ficticious" then how is it your body wants to slide across a bench seat in a car if it takes a corner fast? I think you've researched too much on Wikpedia, try a real book or manual on ballistics.

Larry Gibson

[Iron Mike Golf]

...Somebody schooled in long-range techical ballistics please explain what "going to sleep" really is....Gear

Disclaimer: I am not a ballistician.

From what I have read and understand, "going to sleep" is a dampening of the helixes (I think "spirograph pattern" due to dynamic stability.

http://www.nennstiel-ruprecht.de/bullfly/fig12.htm

As I understand it, this is caused by bullet yaw at the moment it leaves the muzzle. Dynamic stability causes the diameter of the pattern to decrease over time (and range). Gyroscopic stability resists changes to the direction of flight due to off-axis aerodynamic pressures.

================================================== =======

Larry,

In the same article is a diagram relating gyroscopic stability to dynamic stability:

http://www.nennstiel-ruprecht.de/bullfly/stabtria.htm#header

Seems to me that you can affect the overall stability of a bullet by changing the rotational velocity and and get into unstable conditions by either spinning the bullet too slow or too fast.

Also, in that article, it is stated "rotational velocity is much less damped than the transversal velocity (which is damped due to the action of the drag)" on this page:

http://www.nennstiel-ruprecht.de/bullfly/fig14.htm

The author author states that dynamic stability is based on 5 aerodynamic coefficients and "because these coefficients are hard to determine, it can become very complicated to calculate the dynamic stability factor, which varies as a function of the momentary bullet velocity. " (emphasis mine)

That makes me think defining (and calculating) a threshhold is a difficult proposition. It would be a threshhold for a particular bullet, a particular load, at a particular range.

Jeff

[Larry Gibson]

Gear

All of the loads you show are above the 120,00 - 140,000 RPM of the threshold to begin with, actually above 140,000 RPM. Again you mention "limit" and the RPM threshold is not a limit. In your examples you are using 2 slow burning powders, not medium burning powders as I stated in the general RPM threshold description. Using slow burning powders is one of the primary methods to push the RPM threshold upwards. That is what you are doing with your examples; starting at or above 140,000 RPM. The point of the test I gave you to do is to start below or near 120,000 RPM and work up. That way you will see where accuracy is best with that rifle using whatever cast bullet, etc. and where the RPM threshold is as that is where accuracy then gets worse.

To paraphrase you; Gear, don't you read ANYTHING I say?

Close but no cigar, try reading the ballistics book I gave you the title of and try the test with that '06 following my directions. First you will learn and second you will see.

Larry Gibson

[Larry Gibson]

Iron Mike Golf

From what I have read and understand, "going to sleep" is a dampening of the helixes (I think "spirograph pattern" due to dynamic stability.

That is correct, the yaw and precessions cause a helix also. However, we're talking jacketed bullets here "going to sleep" and they (at least any quality jacketed bullet) will not have any where near the imbalances we are talking with cast bullets. Thus the rotation stability overcomes the yaw and effect of precession and the bullet settles down or "goes to sleep".

http://www.nennstiel-ruprecht.de/bullfly/fig12.htm

As I understand it, this is caused by bullet yaw at the moment it leaves the muzzle. Dynamic stability causes the diameter of the pattern to decrease over time (and range). Gyroscopic stability resists changes to the direction of flight due to off-axis aerodynamic pressures.

Exactly correct as I stated.

================================================== =======

Larry,

In the same article is a diagram relating gyroscopic stability to dynamic stability:

http://www.nennstiel-ruprecht.de/bullfly/stabtria.htm#header

Seems to me that you can affect the overall stability of a bullet by changing the rotational velocity and and get into unstable conditions by either spinning the bullet too slow or too fast.

This is also very true as with different twists using the same load/bullet you can measure the stability of a bullet by measureng the BC (done by measuring the time of flight; usually between muzzle and a minimum of 100 yards). Using a 175 gr MK in 10, 12 and 14" twist barrels with the same load and relatively the same velocity we find the 12' twist to give the highest BC and the 10 and 14" twist to give lower BCs. This translates to the 10' twist over stabilizing the bullet and the 14" twist understabilizing the bullet. Ech bullet will have an optimum twist where it will be best stabilized and will give the best accuracy.

Also, in that article, it is stated "rotational velocity is much less damped than the transversal velocity (which is damped due to the action of the drag)" on this page:

http://www.nennstiel-ruprecht.de/bullfly/fig14.htm

The author author states that dynamic stability is based on 5 aerodynamic coefficients and "because these coefficients are hard to determine, it can become very complicated to calculate the dynamic stability factor, which varies as a function of the momentary bullet velocity. " (emphasis mine)

All correct.

That makes me think defining (and calculating) a threshhold is a difficult proposition. It would be a threshhold for a particular bullet, a particular load, at a particular range.

In the case of cast bullets with much larger potential for imbalance it is a threshold based on the particular bulet (design, alloy and fit) and the particular load (acceleration rate). If by "range" you mean the velocity or RPM then that also is correct.

BTW; I want to thank you for bothering to actually research ballistic information from a creditable sourse.

Larry Gibson

[Iron Mike Golf]

Larry,

By range, I meant distance down range (which gets to velocity at that range). My thinking is forward velocity drops to the point it is no longer matched to rotational velocity. I have no idea (nor estimate) whether that would occur with practical shooting distances.

Another thought I had was about deformation of the bullet owing to rotational forces. We know that a fluid drop that is spun deforms (that is one way to measure surface tension). I could see it being possible for a cast bullet to undergo plastic deformation if spun fast enough. I would expect asymmetry resulting in a chaotic grouping.

[onesonek]

Onesonek

"Larry thinks the paper protects the boolit well enough during launch to account for the great increase in RPM potential, and it might, but what about outside the gun?"

Consider that the PP does protect the cast bullet, thus there is less unwanted imbalance done to the cast bullet during acceleration (launch). The less unbalanced the bullet is (or the more balanced the cast bullet is) The less the centrifugal force of higher RPM has to act upon and the bullet is more accurate at higher velocity. Basicly simple in that the PP protects and supports the cast bullet preventing obturation, setback, sloughing, etc. to a much higher velcoity. May not be able to convince gear of that but him not being convinced does not make it a proven fact. Perhaps he has some scientific reason why pwdawg can shoot the 311284 PP'd at 3000 fps with excellent accuracy but he nor any one else can/is shooting the same 311284 naked at 3000 fps with equal accuracy?

Larry Gibson

First let me say, by being so new to cast, I'm just trying to absorb and learn as much as possible, as I will never get caught up with some of you in actual shooting or experimentation.
With that said,,,,,

Ok, I can agree with on certain points, others not so much. RPM 's definately have influence's, but I think for different reasons than you state. But Junoir is also correct, that a jacket can be spun so fast to create failure.

First lets look what RPM's do. For the most part they provide gyroscoptic stabilibity. This to a point, negates minor imperfections in balance issues. And then, to over come or reduce some effects of atmospheric conditions. With the first being the most important!!!
It is generally accepted that a GSF (gyroscoptic stability factor ) of 1.00, stabilizes a given projectile. Now we all know that RPM's degrade with range, at a much much slower rate than velocity. But virtually everything we shoot, is overstabilized to a degree, just generally more so with cast, or so it seems. Some more than other's. I won't state any hard numbers, as I'm going from memory,,,,but the typical flatnose cast I have run in the ballistic program, are way high in GSF regardless, with typical small and medium bore twist rates,,,even when slowed down 2, 3, or 4 inches. So indeed, faster twist rates than necessary with, cast make things considerabally more difficult, as they are less forgiving than their jacketed counterparts.

All bullets leave the muzzle with some helix in the flight. This is caused by the yaw, unless twist and speed is such yaw is absent at the muzzle. But if this were the case, (having a GSF of 1.00), stability would be lost relatively quickly down range. This is why in the long range world, they prefer a GSF of about 1.5. You don't get as much yaw, leaving with less helix, and it Sleeps at a much quicker rate, or closer range. Yet is still above GSF 1 at extreme ranges. Sleep occurs when eventually the air pressure overcomes the centrifugal force of the yaw itself.
Hence I agree with 44man's thoughts.

While in the helix stages of flight, the helix itself will lessen with range due to a very slight amount of rpm degradation and more so, sleep time. (Albeit, this a phenomenon I have yet to fully understand. But I know it is, so I don't worry about it, unless playing at extreme range with some rigs I shoot)
However, the more the bullet/boolit is over spun/stabilized, the longer it takes. But the helix size itself will remain consistent or linear, albeit, decreasing with with range eventually dissipating to none.
I do agree it will get larger or rather, erratic do to factors directly related to rpm, but I believe imbalance is not the major cause, unless grossly so. More about that in a bit.

Now I don't quite buy into the nose slump or setback, like Gear, as this would have detrimental effects on PP boolit as well., specially one that is lube grooved. And with PP's accuracy, I just don't believe it is happening with either PP or naked. I do agree that the PP itself does project the boolit shank however as you say. But if there was any major setback or slump here which would be expected if all else is equal in using lube groove PP, to a naked boolit, one would see some major accuracy issues as well with the PP. Hence I don't believe their is any setback or slump of the PP smooth shanked or lube groove bullet,,,even with a softer alloy.
Sloughing is another whole different game however.

First I believe all bullet/boolit's obturate PP'd or naked, even the all copper/mono's will, given enough pressure. About the only ones that won't, are the steel or tungten core jacketed at normal pressures. Just I believe that a compressed PP jacket, has greater shear strength, than naked lead alloy's, hence less slip/slough with minor dia. differences within the bore. More about that later too.
And naturally, being there is no direct contact between the cast and the bore, no sloughing or abnormal deformations occur, creating minor imperfection on the boolit surface. With naked boolit alloy's, obturation with minor difference's within the bore's dia., take some time, that don't happen immediate enough in some. Hence you get some sloughing, leaving minor imperfections in the bearing surface, even if all but invisible to the naked eye. I guess I look at sloughing as leading to a point, even if it is very little indeed. Where as the PP is protected as you say.

Now rather than imbalance being compounded by excessive rpm, I believe it is these imperfections in the boolits surface, that are creating erratic helix's and poor grouping in general, with fluctuations in air flowing over the surface. Although imbalance certainly would have effects as well, that I agree, just not to the greater extent, as gyro will hold these in check up to a point, again unless there is a gross balance issue.
I think it really goes back to matching alloy to pressure in the long run with naked boolits. In order keep sloughling/leading, or any other pressure induced anomalies on the bearing surface minimized as much as possible.

I do think you make some valid points Larry, as does Gear. I just see it as there is no real chicken or egg thing going on here. No absolutes, hard rules, just that naked boolits are more influnced by all aspects, making it harder all the way around, to get consistency.
But for the most part, we are over stabilized as a whole, and so, yes RPM has a major part. But like Gear, not necessarily agreeing on all the reasons.
But going by the law of averages, your rpm threshold has some merit, just no absolutes, as alloy/pressure, bore consistencies in my mind, have slighlty more influence. But all are tied together when pushing the limits, making it for a challenge to say the least, with naked boolits.

Now I could be all wet with the above, but thats just how I interpret of what I have learned here in general, and or otherwise, with years of shooting J's before.
Now before I get jumped on that statement,,,, I know Jacketed and Cast are two different breeds of cat altogether!! So we really don't need to go there.. But the physics of stability are relatively the same.

I try to keep an open mind however, as my thoughts have been wrong in the past. And I'm certainly still learning in this game, so much so, that I remind myself to listen to all and glean what I can.

[madsenshooter]

44man, how far was the paper target? Did you do any tests to determine at what distance the boolit came apart? And how far it was effective in crow after it had come apart?

Not really relevant to this discourse, but 303 guy, I've seen shrapnel from a hit two feet away kill a crow. That was with a jacketed bullet and I was pretty amazed to see the bullet hit the ground and then the crow fall dead! Sometimes, close is close enough! I should say the same about all this expounded theory. One would have to have the bullet travel down to a gnat's butt and 2 loads, one that produces the helix, and one that doesn't in order to prove that the helix even exists. Since I'm not shooting gnats, I don't care. Therefore, I should stop reading it, and I promise to not comment anymore, the crow was more important to me.

[felix]

Gyroscopic stability resists changes to the direction of flight due to off-axis aerodynamic pressures.

Amen. There are two major off-axis components. One is the boolit leaving the muzzle. Another is the the boolit leaving the SYSTEM. The barrel exhibits a vibe pattern, while the system exhibits a recoil correction. Both induce independent wave forms into the boolit which are carried forward to target.

... felix

[Larry Gibson]

Iron Mike Golf

By range, I meant distance down range (which gets to velocity at that range). My thinking is forward velocity drops to the point it is no longer matched to rotational velocity. I have no idea (nor estimate) whether that would occur with practical shooting distances.

Many, many tests (Hatcher, the arsenals, etc.) have conducted tests and found a properly stabilised bullet remains stable through out the maximum range of flight. At the cast bullet distances of 1000 yards or less, probably 300 yards or less the los of rotation velocity (RPM) is negliable. There are some exceptions such as wadcutters but we are not talking wadcutters at high velocity.

Another thought I had was about deformation of the bullet owing to rotational forces. We know that a fluid drop that is spun deforms (that is one way to measure surface tension). I could see it being possible for a cast bullet to undergo plastic deformation if spun fast enough. I would expect asymmetry resulting in a chaotic grouping.

If we had a perfectly balance cast bullet on muzzle exit we might see that. However, since we don't often have perfectly balanced cast bullets on muzzle exit, long before a reasonable alloy we use (even 50/50 WW/pb) reaches plastic deformation the centrifugal force will be strong enough to cause the bullet to depart from the line of flight on a helical spiral or a complete tangent.

Larry Gibson

[Iron Mike Golf]

Amen. There are two major off-axis components. One is the boolit leaving the muzzle. Another is the the boolit leaving the SYSTEM. The barrel exhibits a vibe pattern, while the system exhibits a recoil correction. Both induce independent wave forms into the boolit which are carried forward to target.

... felix

I would add (or separate out) a third: Bullet near the muzzle and under acceleration effect of propellant gases. I differentatiate this from "leaving the muzzle" as there are 2 transitions. The other being transitioning from rotating aroung the bore axis to rotating aroung the center fo gravity.

[Larry Gibson]

onesonek

First let me say, by being so new to cast, I'm just trying to absorb and learn as much as possible, as I will never get caught up with some of you in actual shooting or experimentation.
With that said,,,,,

Ok, I can agree with on certain points, others not so much. RPM 's definately have influence's, but I think for different reasons than you state. But Junoir is also correct, that a jacket can be spun so fast to create failure.

First lets look what RPM's do. For the most part they provide gyroscoptic stabilibity. This to a point, negates minor imperfections in balance issues. RPM or factually the centrifugal force caused by RPM never negates the imbalances. This why even with the finest of jacketed match bullets we shoot groups instead of them going into one hole.And then, to over come or reduce some effects of atmospheric conditions. With the first being the most important!!!
It is generally accepted that a GSF (gyroscoptic stability factor ) of 1.00, stabilizes a given projectile. Now we all know that RPM's degrade with range, at a much much slower rate than velocity. But virtually everything we shoot, is overstabilized to a degree, just generally more so with cast, or so it seems. Some more than other's. I won't state any hard numbers, as I'm going from memory,,,,but the typical flatnose cast I have run in the ballistic program, are way high in GSF regardless, with typical small and medium bore twist rates,,,even when slowed down 2, 3, or 4 inches. So indeed, faster twist rates than necessary with, cast make things considerabally more difficult, as they are less forgiving than their jacketed counterparts. All that is correct; every bullet will have a specifice rate of twist where it will be the mose stable.

All bullets leave the muzzle with some helix in the flight. This is caused by the yaw, unless twist and speed is such yaw is absent at the muzzle. But if this were the case, (having a GSF of 1.00), stability would be lost relatively quickly down range. This is why in the long range world, they prefer a GSF of about 1.5. You don't get as much yaw, leaving with less helix, and it Sleeps at a much quicker rate, or closer range. Yet is still above GSF 1 at extreme ranges. Sleep occurs when eventually the air pressure overcomes the centrifugal force of the yaw itself.
Hence I agree with 44man's thoughts.

While in the helix stages of flight, the helix itself will lessen with range due to a very slight amount of rpm degradation and more so, sleep time. (Albeit, this a phenomenon I have yet to fully understand. But I know it is, so I don't worry about it, unless playing at extreme range with some rigs I shoot)
However, the more the bullet/boolit is over spun/stabilized, the longer it takes. But the helix size itself will remain consistent or linear, albeit, decreasing with with range eventually dissipating to none.
I do agree it will get larger or rather, erratic do to factors directly related to rpm, but I believe imbalance is not the major cause, unless grossly so. More about that in a bit.

The problem here is you're thinking there is only one helix. That is not correct. Indeed yaw and precessions cause a helical spiral intiially in most bullets on muzzle exit. It is larger with some than others. They do go to sleep down range. However, do not confuse that helical spiral with the one caused by excessive centrifugal force. They are two different helical spirals or a possible tangent caused by two seperate actions. Whether or not you agree with the helical spiral or tangent being caused by excessive RPM/centrifugal force note you are not disagreeing with me but the laws of ballistics as I quoted that from ballistic manuals. Its not My "theory" but fact.


Now I don't quite buy into the nose slump or setback, like Gear, as this would have detrimental effects on PP boolit as well., specially one that is lube grooved. And with PP's accuracy, I just don't believe it is happening with either PP or naked. I do agree that the PP itself does project the boolit shank however as you say. But if there was any major setback or slump here which would be expected if all else is equal in using lube groove PP, to a naked boolit, one would see some major accuracy issues as well with the PP. Hence I don't believe their is any setback or slump of the PP smooth shanked or lube groove bullet,,,even with a softer alloy.
Sloughing is another whole different game however.

First I believe all bullet/boolit's obturate PP'd or naked, even the all copper/mono's will, given enough pressure. About the only ones that won't, are the steel or tungten core jacketed at normal pressures. Just I believe that a compressed PP jacket, has greater shear strength, than naked lead alloy's, hence less slip/slough with minor dia. differences within the bore. More about that later too.
And naturally, being there is no direct contact between the cast and the bore, no sloughing or abnormal deformations occur, creating minor imperfection on the boolit surface. With naked boolit alloy's, obturation with minor difference's within the bore's dia., take some time, that don't happen immediate enough in some. Hence you get some sloughing, leaving minor imperfections in the bearing surface, even if all but invisible to the naked eye. I guess I look at sloughing as leading to a point, even if it is very little indeed. Where as the PP is protected as you say.

I'll post some phot's in the next post for you to study.

Now rather than imbalance being compounded by excessive rpm, I believe it is these imperfections in the boolits surface, that are creating erratic helix's and poor grouping in general, with fluctuations in air flowing over the surface. Although imbalance certainly would have effects as well, that I agree, just not to the greater extent, as gyro will hold these in check up to a point, again unless there is a gross balance issue.
I think it really goes back to matching alloy to pressure in the long run with naked boolits. In order keep sloughling/leading, or any other pressure induced anomalies on the bearing surface minimized as much as possible.

As I've stated in this post I quoted from Ballistics manuals, if you choose not to believe that then so be it. That does not make you correct however.

I do think you make some valid points Larry, as does Gear. I just see it as there is no real chicken or egg thing going on here. No absolutes, hard rules, just that naked boolits are more influnced by all aspects, making it harder all the way around, to get consistency. There some hard rules; its called ballists, laws of physics and the laws of gravity. Again, if you choose not to believe them.......
But for the most part, we are over stabilized as a whole, and so, yes RPM has a major part. But like Gear, not necessarily agreeing on all the reasons.
But going by the law of averages, your rpm threshold has some merit, just no absolutes, as alloy/pressure, bore consistencies in my mind, have slighlty more influence. But all are tied together when pushing the limits, making it for a challenge to say the least, with naked boolits. I certainly agree, the RPM threshold is not an "absolute". That is why I cant tell exactly at what RPM it will happen, it is not a limit but can be raised or lowered But I can tell you that when you push a cast bullet fast enough with a fast twist it will happen.

Now I could be all wet with the above, but thats just how I interpret of what I have learned here in general, and or otherwise, with years of shooting J's before.
Now before I get jumped on that statement,,,, I know Jacketed and Cast are two different breeds of cat altogether!! So we really don't need to go there.. But the physics of stability are relatively the same. Not 'relative the same" but they are the same.

I try to keep an open mind however, as my thoughts have been wrong in the past. And I'm certainly still learning in this game, so much so, that I remind myself to listen to all and glean what I can.

I suggest you keep an open mind and perhaps you might want to read Understanding Firearm Ballistics by Robert A. Rinker. That is the same book on ballistics I recomended to Gear. It is a good basic book for the beginning study of ballistics. Not hard reading and in common style english so it's pretty easy to understand.

Larry Gibson

[Larry Gibson]

.......... The other being transitioning from rotating aroung the bore axis to rotating aroung the center fo gravity.

Might be where the precession I mentioned comes from, eh?

Larry Gibson

[geargnasher]

Gear

All of the loads you show are above the 120,00 - 140,000 RPM of the threshold to begin with, actually above 140,000 RPM. Yes, that's true. I pushed the threshold. Kinda make the concept of having a threshold to go by pretty useless, doesn't it? Again you mention "limit" and the RPM threshold is not a limit. Yes, I mentioned limit. I reached the accuracy/velocity limit with that gun and boolit with two different powders. In your examples you are using 2 slow burning powders, not medium burning powders as I stated in the general RPM threshold description. Why on earth woud I want to downgrade my velocity and powder just to prove your theory? I figured I proved SOME limit well enough with those tests, just not sure if I proved you or Richard Lee more right. Using slow burning powders is one of the primary methods to push the RPM threshold upwards. That is what you are doing with your examples; starting at or above 140,000 RPM. The point of the test I gave you to do is to start below or near 120,000 RPM and work up. What would that prove? That I could LOWER my accuracy/velocity limit? Heck, I can do that just by changing alloy. That way you will see where accuracy is best with that rifle using whatever cast bullet, etc. and where the RPM threshold is as that is where accuracy then gets worse.

To paraphrase you; Gear, don't you read ANYTHING I say?

Close but no cigar, try reading the ballistics book I gave you the title of and try the test with that '06 following my directions. First you will learn and second you will see.

Larry Gibson

Gotto go cast some more 266673's, be back to respond to the rest of this after a while, particularly your smartass Wikipedea comment. What I said is introduced in a class called physics for physicists and engineers (one), and if you can't understand how important inertial frame of reference is, you won't get much about how "centrifugal force" really acts on a boolit.

Gear

[Larry Gibson]

Onesonek

If you don't think cast bullet noses, whether PP'd or naked, obturate, setback, slough, etc. take a look at the two photo's and explane the rifling marks on the bullet nose. also not the one is only on one side. If you look closely you can also see the scraper groove and the lube groove have collapsed where the rifling is the deepest on the bullet nose bearing surface.

If they don't obturate, slough, setback etc. can you explain?

Larry Gibson

[Larry Gibson]

Gear

If we don't keep this thread civil it will get locked. Please refrain from the personal remarks, making those will get you nor the rest of us anywhere. Thank you.

BTW; I do fully understand how centrifugal force acts on a bullet. I have been studying and testing the subject for many years.

Larry Gibson

[Iron Mike Golf]

Might be where the precession I mentioned comes from, eh?

Larry Gibson

Most certainly precession is started by by the transition from interior to exterior ballistics. Interesting results have been obtained by using rebated boattails to mitigate the propellant gases acting on the base when the bullet is no longer constrained by the bore. I have also read of a rebeat assisting by disrupting the flow of gas foward along the bullet surface where it can pile up infornt of the bullet, create turblulence it has to pass through (much like the nozzle of a garden-cariety garden hose).

I have also read of a lateral translational displacement during this transional phase.

[waksupi]

Oh, we may not lock it, but someone may be missing from the board for ten days or so.

[onceabull]

Since it's known that all the top finishers in the CBA matches are shooting Ultramags and Lazzeronis(NOT) let us get serious about this cast boolits at jacketed velocities,with accuracy game.. after all, Veral's been in business a long time selling that story...Onceabul;l

[leftiye]

Gear

BTW; I do fully understand how centrifugal force acts on a bullet. I have been studying and testing the subject for many years.

Larry Gibson

Was that 20 years experience or one year of learning 20 times? Thas kinda like - sayin' it don't make it so.

For those of us who are intellectually challenged you could focus on the issues presented to you rather than polluting them first, and then running them through a potato masher (or equally likely, just ignoring the question and answering something else). Saying that you comprehend something, and then telling the other guy he's wrong will never get it. Gear did an experiment, he detailed the results to us. He did not search for your barrier or threshold, he exceeded where you said it was and asked how that could happen. DrB had the same problem, you refused to study his data and respond to his questions and expected him to do it your way and then POSSIBLY (not likely) you would answer his questions. 'Tain't fair (another surprise - not).

[45 2.1]

All of the loads you show are above the 120,00 - 140,000 RPM of the threshold to begin with, actually above 140,000 RPM. Again you mention "limit" and the RPM threshold is not a limit. In your examples you are using 2 slow burning powders, not medium burning powders as I stated in the general RPM threshold description. Using slow burning powders is one of the primary methods to push the RPM threshold upwards.

Looks like your taking a good beating here on this thread Larry......... Your observation should indicate to you that the problem is pressure related rather than any limit on so called RPM problems you have...... since the slow burners can achieve the same or greater velocities with excellent accuracy in the same cartridge/boolit weight at lower than pressure inducing inaccuracy ranges. Think about it. Loading manuals with pressure figures will tell you where this occurs if you look enough. Don't bother with any rebutales till you learn more. My machine is down presently and probably won't be up for awhile. Ya'll play nice now.

[onesonek]

Larry,,,first let me say, that in some, I could have used a better choice of words. As in this case,,,
"First lets look what RPM's do. For the most part they provide gyroscoptic stabilibity. This to a point, negates minor imperfections in balance issues."------ "RPM or factually the centrifugal force caused by RPM never negates the imbalances. This why even with the finest of jacketed match bullets we shoot groups instead of them going into one hole."

Minimizes, in place of negates would have been more correct.
Beyond that, even with the finest jacketed,,,,, or even with the bullet/boolit being in perfect balance, you have harmonics in the equation, that often changes, sometimes quite rapidly. Then throw in the shooters fundementals. These have as much effect if not more in some situations, everything else bieng near perfect as possible.

"The problem here is you're thinking there is only one helix. That is not correct. Indeed yaw and precessions cause a helical spiral intiially in most bullets on muzzle exit. It is larger with some than others. They do go to sleep down range. However, do not confuse that helical spiral with the one caused by excessive centrifugal force. They are two different helical spirals or a possible tangent caused by two seperate actions. Whether or not you agree with the helical spiral or tangent being caused by excessive RPM/centrifugal force note you are not disagreeing with me but the laws of ballistics as I quoted that from ballistic manuals. Its not My "theory" but fact."

I won't argue that and agree. However, the secondary helix could be attributed to harmonics as much as balance, just as easily.


"As I've stated in this post I quoted from Ballistics manuals, if you choose not to believe that then so be it. That does not make you correct however."
"There some hard rules; its called ballists, laws of physics and the laws of gravity. Again, if you choose not to believe them......."
I don't argue the laws and rules, just sometimes the conjecture sometimes surrounding them. As I said, you made some valid points.

" But the physics of stability are relatively the same."---" Not 'relative the same" but they are the same.
Quite often I will speak loosely in generalities, which allows to be taken too literally, or out of context. But we are on the same page in general!

"If you don't think cast bullet noses, whether PP'd or naked, obturate, setback, slough, etc. take a look at the two photo's and explane the rifling marks on the bullet nose. also not the one is only on one side. If you look closely you can also see the scraper groove and the lube groove have collapsed where the rifling is the deepest on the bullet nose bearing surface.

If they don't obturate, slough, setback etc. can you explain?"

I said they obturate, just didn't believe setback was enough to create a major balance problem., unless it was extensive.
As to the pic's,,,,,, that was my point of alloy matching to pressure on a bare boolit.
The one clearly shows, it had past it's strength to pressure capability, but not to the point of completely stripping. This is going to raise hell with accuracy no matter the rpm.
Now how the same bullet in a paper jacket handles it at even higher pressures with less ill effects is what I consider a phenomena, that is also hard for me to wrap my head around.
As stated I believe the paper has greater shear strength, resisting stripping better. But I can't see how it has any compressive strenght to stop, major setback or uneven colapse of the lube grooves, But evidently it accomplishes this some how and greater pressures than the naked can handle.

[Larry Gibson]

Onesonek

“Minimizes” would have indeed been much more correct and a word in that context of which I agree.

“However, the secondary helix could be attributed to harmonics as much as balance, just as easily”

Not quite, harmonics causing flyers or inaccuracy does not put the bullet into a helical spiral. Harmonics can cause the bullet to got off on a tangent. It will continue in the direction of that tangent for the duration of its flight. Let us ask ourselves if my bull barreled M70 target in .308W will shoot every quality jacketed bullet at 2600 fps with sub moa accuracy then why won’t it shoot any better than 6 moa (just an example figure) at 2600 fps with cast bullets? Is it barrel harmonics and just how whippy do we think a 26” bullet barrel is? The adverse affects of bad barrel harmonics and the RPM threshold can appear to have the same results, especially at 100 yards or less. However, they are seperate actions with actually different results.

You also make some valid points and now that I understand the “generalities” I can certain see we are agreeing a whole lot more, nice to be on the same page with you.

Yes, it is hard to wrap ones head around how the PP can be that “protective” of the same cast bullet allowing it to shot accurately and a higher velocity, took a while for me to fully understand it also. A good PP really does allow that though and I think you are beginning to see that.

Again, thanks for the productive input.

Larry Gibson

[Larry Gibson]

leftiye

Was that 20 years experience or one year of learning 20 times? Thas kinda like - sayin' it don't make it so.

Be nice if you kept it civil.

For those of us who are intellectually challenged you could focus on the issues presented to you rather than polluting them first, and then running them through a potato masher (or equally likely, just ignoring the question and answering something else). Saying that you comprehend something, and then telling the other guy he's wrong will never get it. Gear did an experiment, he detailed the results to us. He did not search for your barrier or threshold, he exceeded where you said it was and asked how that could happen.

I didn't "pollute the problem" at all. Gear was using his tests to show the RPM threshold doesn't exist. I merely pointed out that he was already above the RPM threshold and that he should run the test I suggested to find it.

DrB had the same problem, you refused to study his data and respond to his questions and expected him to do it your way and then POSSIBLY (not likely) you would answer his questions. 'Tain't fair (another surprise - not). Ou contraire; I did study his data nad pointed out the potential cause of those pesky little flyers he and Bullshop are plagued with. I believe he failed to respond to my suggestions as to the cause. He also asked me to start this thread BTW so "we" could discuss the RPM threshold here. His absense here is duly noted indeed:groner:

Larry Gibson

[Larry Gibson]

45 2.1

All of the loads you show are above the 120,00 - 140,000 RPM of the threshold to begin with, actually above 140,000 RPM. Again you mention "limit" and the RPM threshold is not a limit. In your examples you are using 2 slow burning powders, not medium burning powders as I stated in the general RPM threshold description. Using slow burning powders is one of the primary methods to push the RPM threshold upwards.

Looks like your taking a good beating here on this thread Larry......... "taking a beating"? Come on Bob, this has been, with a couple exceptions, a pretty good discussion. Your observation should indicate to you that the problem is pressure related rather than any limit on so called RPM problems you have...... since the slow burners can achieve the same or greater velocities with excellent accuracy in the same cartridge/boolit weight at lower than pressure inducing inaccuracy ranges. Do you have any idea why ballistics is seperation into 3 parts; internal, external and terminal? Might be because what happens, cause and effect, in one of them may or may not be related to the others. The imbalances to the bullets occur during castind, sizing, loading and under acceleration which are before and during internal ballistics. The centrifugal force acting upon those imbalances occurs during flight. Think about it. Loading manuals with pressure figures will tell you where this occurs if you look enough. Bob, you might want to "think about it" as you seem to have forgotten that I measure the actual pressures of my loads. I don't have to consult a manual, Quick load or other "guestimation" method. (deleted last part here) like you say; let's play nice. Enjoy the computer down time.

Larry Gibson

[crabo]

It seems like this subject and the 6.5 Swede seem to create the most passion on this board.

Oh yeah, and then there's Freedom Arms....

[grouch]

Actually I was aware that physicists didn't like the term "centrifugal force" but since I left school nearly 50 yrs ago and can't remember their name for it, I regard it as a matter of semantics. The force is there all right. If I remember correctly, it pulls tangentially instead of radially, hence the problem with the name. In any case, my point was that as a study of the effect on bullets of different diameters, maybe "rim speed"might be a more logical approach than RPM. Just a suggestion,
Grouch

[geargnasher]

Actually I was aware that physicists didn't like the term "centrifugal force" but since I left school nearly 50 yrs ago and can't remember their name for it, I regard it as a matter of semantics. The force is there all right. If I remember correctly, it pulls tangentially instead of radially, hence the problem with the name. In any case, my point was that as a study of the effect on bullets of different diameters, maybe "rim speed"might be a more logical approach than RPM. Just a suggestion,
Grouch

You remember corrctly, Grouch. The difference is the "inertial frame of reference", meaning that if your frame of reference is the shooter, the forces appear to, but do not actually radiate outward from center, while if you're riding on the boolit (like the bands are, or lube in the grooves is), the force acting outward from the boolit is the inertial tendency of the surface to resist being pulled in a continuous arc, and thus want to constantly project in a straight line tangent to the boolit's surface. In other words it's a vector, not an outward pull. Understanding the difference is key to understanding how a boolit will wobble in flight, and the perception that it's actually a radial force as it appears from a fixed point outside the boolit is bound to cause confusion.

Gear

[geargnasher]

I didn't "pollute the problem" at all. Gear was using his tests to show the RPM threshold doesn't exist. I merely pointed out that he was already above the RPM threshold and that he should run the test I suggested to find it.
Larry Gibson[/B]

NO. I was not using those tests to show that rpm threshold didn't exist. What I said is in post #77, nothing about proving the RPM threshold doesn't exist. I was in fact using those tests to show that there IS an accuracy/velocity limit, same as you observe albeit a little higher in the example due to the slower powder, and that there happens to be another possible explanation for it that coincides exactly with Lee's hypothesis. I don't think Lee's hypothesis is the best possible explanation either, because it discounts too many other factors and has some holes in it too, but I think it's interesting to point out that you two have totally different ideas and explanations for the same phenomena.

You yourself state here: "Using slow burning powders is one of the primary methods to push the RPM threshold upwards.", so in fact I was STILL actually within what you term the RPM threshold in my example until the point that accuracy began to degrade, it's just that I'd pushed the threshold a bit with my powder choices. The accuracy deterioration coincided as closely as I can figure with the peak pressure exceeding the strength of my alloy. Don't you think that merits some consideration?

Gear

[geargnasher]

What's amazing, is how much energy it takes to get a boolit up to the terminal RPM. Up to a third of the amount given to the VELOCITY. ... felix

That went clear over my head at first in terms of relevance to RPM theory. I haven't tested it myself, but it seems to be fairly common knowledge that the slower the twist, the faster the velocity can be pushed with the same accuracy. Larry pins it down to a range of RPM and has shown in the past how twist rate and velocity are inverse as long as RPM stays in that range. Pressure is what it takes to accelerate the boolit both directions (forward and against the rifling). If the rifling has a slower rate, then the boolit can be pushed faster with the same pressure and force acting against the boolit by the lands. So is pressure the limiting factor and RPM merely a yardstick?

Gear

[303Guy]

Pressure is what it takes to accelerate the boolit both directions (forward and against the rifling)..... So is pressure the limiting factor and RPM merely a yardstick?My thoughts exactly when I read felix's post. But that's a massive rotational energy!

[felix]

So is pressure the limiting factor and RPM merely a yardstick? Gear

BINGO!!!! ... felix

Circumferential speed would be a better blow-up measurement factor when compared to native RPM because the radius of the projectile would be included in the calcs. ... felix

[BABore]

BINGO!!!! ... felix

Which is the primary reason Lil Gun works well for HV loads in the Hornet and simlilar sized rounds. Lil Gun will exceed WW 296 velocities by 100-200 fps and do it at 7 to 10 kpsi less pressure.

[onesonek]

So does that mean, for example,,,one uses a Metric meter stick for the 7.62 boolits along with Pascal, and a US Standard yardstick for the .308 boolits with PSI?

[Larry Gibson]

Gear’s post with his tests was in response to my request he conduct the test to find the RPM threshold. His appeared to be at or above the RPM threshold for his load/components. The test I requested he do would have told when the load was most accurate and when it started to lose accuracy at it’s RPM threshold. His test simply did not meet the criteria of what I requested he test.

“So is pressure the limiting factor and RPM merely a yardstick? Gear”

I’ll have to say that Starmetal, 45 2.1, probably BaBore, myself and a few others have disproved that one. Gear is also correct in his previous statements questioning that pressure is the limiting factor. My .308W load with a 311466 that runs 2600+ fps with excellent accuracy to 300 yards (farthest tested) also runs at a measured (Oehler M43) 40,000+ psi not guessed at by consulting manuals, using QuickLoad or any other "guestimation" method. If pressure was the “limiting factor” then, according to Lee’s chart that 16 – 18 BHN bullet should have reached its “limit” between 20,000 and 23,000 psi and accuracy should have gone south there. Yet I push them at 2600+ fps/40,000+ psi with 1 ½ moa. So how is that if pressure is the limiting factor?

Let’s consider what else I’m doing; loading procedures are standard for cast bullet accuracy (fire formed NS'd cases and bullet sizing to fit the throat) with no secret ingredients of buffers or special cases, the 311466s are cast in a 4 cavity mould with visual inspection only and are not weight sorted, a slow burning powder at 100+ loading density, plain old Javelina lube and Hornady GCs, and use of a regular primer (brand doesn’t seem to make any difference)………so what could be the reason for such accuracy at 2600+ fps at 40,000+ psi? Might it just be because I’m using a 14” twist barrel and controlling the RPM by keeping them at a low rate. At 2600+ fps the RPM is 133,700+ with the 14” twist. In a 10” twist the RPM at 2600+ fps would be 187,200+, probably over the RPM threshold for that alloyed bullet.

Funny how that works isn’t it.

Larry Gibson

[felix]

It appears that Lee's formulas do not take into account the necessary factors, such as rifling depth, for total pressure containment. I overlook his formulas for accuracy prediction. ... felix

[Nrut]

Larry,
Regarding post #112 above:

Is your 1:14 twist barrel OEM to that rifle or is it a custom barrel?
What about the chamber?
Tight neck?
Cut to min. length?
Any other tweaks to the chamber?

Great discussion BTW..


On another note:
There is more than one way to skin a felix..:grin:
hint..

[44man]

Onesonek

If you don't think cast bullet noses, whether PP'd or naked, obturate, setback, slough, etc. take a look at the two photo's and explane the rifling marks on the bullet nose. also not the one is only on one side. If you look closely you can also see the scraper groove and the lube groove have collapsed where the rifling is the deepest on the bullet nose bearing surface.

If they don't obturate, slough, setback etc. can you explain?

Larry Gibson
Yes, I agree, slump is not only real but so common with what fellas shoot they would not believe it. The same thing you have shown is what happens to the Lee 459-500-3R in the 45-70 with BP. BPCR shooters found it has caused problems, many times the nose will upset off center. 20 to 1 or 30 to 1 is not strong enough to resist upset.
Think of the dead soft Keith boolit that does not remain a Keith in any sense of the word. It turns into a RNFP very easy so why not just start with a RNFP? It will not tend to slump off center as much. Better start in a forcing cone too.
Maybe an old revolver with oversize throats will benefit from expansion to fit and obturate to seal and hard boolits cause problems but that is a gun problem and it will never do what it should.
I will always believe that a fresh cast boolit in hand should never look any different after it is fired so different pressures, velocities, powders and twist rates need the alloy changed to keep the boolit intact.
I am about as hard headed as I can get when it comes to fit and boolit integrity! 8-)
A man will ask a question and 999 answers will be to make the boolit softer when not a single person knows what the boolit causing the problem is actually doing.
Now some more to think about. I have always believed that not only boolit length but the length of the drive area is important to match twist. Just changing drive length without changing length has resulted in key hole targets.
Now the pictures you showed have much longer rifling contact then the as cast. Just how much does this affect twist rates?
I have shot too many boolits of the same length from a gun with all kinds of results from fantastic to junk, even sideways boolits at 50 yards.

[geargnasher]

It appears that Lee's formulas do not take into account the necessary factors, such as rifling depth, for total pressure containment. I overlook his formulas for accuracy prediction. ... felix

That's what I think too about Lee's approach to only considering peak pressure as an accuracy limit. Any formula that doesn't consider all of the major, known factors is bound to be only a rough guideline at best, and riddled with exceptions. It's also folly to only consider peak average pressure, which really means much less in shooting cast boolits than the curve up to that peak, the longer a slope the better for a safe launch.

Gear

[onesonek]

BINGO!!!! ... felix

Ah Ha,,,now I get it,,,,it's a Game!

Game objective,,, pressure management and accuracy. Game rules,,,,All components of the game, can be changed by the individual player at any time. Winning is achieved by obtaining acceptable accuracy.

[geargnasher]

“So is pressure the limiting factor and RPM merely a yardstick? Gear”

I’ll have to say that Starmetal, 45 2.1, probably BaBore, myself and a few others have disproved that one. Gear is also correct in his previous statements questioning that pressure is the limiting factor. My .308W load with a 311466 that runs 2600+ fps with excellent accuracy to 300 yards (farthest tested) also runs at a measured (Oehler M43) 40,000+ psi not guessed at by consulting manuals, using QuickLoad or any other "guestimation" method. If pressure was the “limiting factor” then, according to Lee’s chart that 16 – 18 BHN bullet should have reached its “limit” between 20,000 and 23,000 psi and accuracy should have gone south there. Yet I push them at 2600+ fps/40,000+ psi with 1 ½ moa. So how is that if pressure is the limiting factor?

Let’s consider what else I’m doing; loading procedures are standard for cast bullet accuracy (fire formed NS'd cases and bullet sizing to fit the throat) with no secret ingredients of buffers or special cases, the 311466s are cast in a 4 cavity mould with visual inspection only and are not weight sorted, a slow burning powder at 100+ loading density, plain old Javelina lube and Hornady GCs, and use of a regular primer (brand doesn’t seem to make any difference)………so what could be the reason for such accuracy at 2600+ fps at 40,000+ psi? Might it just be because I’m using a 14” twist barrel and controlling the RPM by keeping them at a low rate. At 2600+ fps the RPM is 133,700+ with the 14” twist. In a 10” twist the RPM at 2600+ fps would be 187,200+, probably over the RPM threshold for that alloyed bullet.

Funny how that works isn’t it.

Larry Gibson

How can pressure be the limiting factor you ask? Consider what Felix mentioned. I'll bet that the pressure on the sides of the boolit by the lands as it's "torqued up" going down the barrel are the same for a ten-twist at 130k muzzle rpm at 2,000 fps (whatever it is, close enough) as it is for a 14-twist going 130K-ish muzzle rpm at 2600 fps, so decreasing the twist rate of the barrel, all else being the same, would naturally increase the ratio of forward velocity to rotational velocity, and you get a faster boolit out the muzzle with the same force on the boolit's engagement points and same force expended on getting the boolit spinning.

Since a boolit can be reasonably pushed to 130K rpm with accuracy, and the pressure on the lands is still reasonable (meaning that once engraved, the boolit is able to push back on the leading edge of the rifling with equal force at that point without deforming too much,) then it would follow that you could increase the pressure on the base considerably beyond the yield strength of the alloy with no ill effect. The boolit is moving away from the chamber pressure force, anyway, so it isn't receiving the full effect of the 40K psi, and with the same anti-rotational forces as the slower boolit in a ten-twist going on (meaning resistance to forward motion caused by the rifling and the boolit's inertial resistance to the rotational acceleration), the boolit base is really only receiving as much pressure as the faster-twist example, which WAS under the pressure limits theorized by Lee for the boolits used.

One more thing about the slow twist, since the ratio of forward velocity to rotational velocity is changed quite a bit, so is the expansion rate of the burn space in relation to the resistance of the boolit to being spun up. I'm sure you are extremely familiar with the effect that has on how the pressure is utilized: It will lengthen the start-to-peak slope considerably, and as we all know that allows HIGHER peak chamber pressure to be utilized without detriment to the boolit, and thus without detriment to accuracy.

Gear

[Larry Gibson]

Nrut

Is your 1:14 twist barrel OEM to that rifle or is it a custom barrel?
What about the chamber?
Tight neck?
Cut to min. length?
Any other tweaks to the chamber?

It was on a factory Shultz & Larson Palma rifle on a Huskvarna M98 action. The original owner put a half a box of reloads using 190 gr MKs through it and didn't like it because it wasn't accurate.....go figure, 190s in a Palma barrel:groner:

So I got it for $10 from the gunsmith (a good friend) who took it off and rebarreled with a match Pacnor barrel with 10" twist. I guess the original owner was then happy and I sure am happy:bigsmyl2:

I set the barrel back 1/2 thread and rechambered with a minimum spec reamer I have. I put it in a m98 mauser i have in a target stock. When it was a 6.5-308 it would shoot 1/2 moa so the bedding and action work I've done to it are good. It also shoots 1/2 moa now with 155 Palma MKs or the 150 MKs. Head space is set at the minimum. It is not a tight neck as the reamer is minimum for M852/M118LR ammuntion. No other tweaks to the chamber or throat.

Great discussion BTW..

With a couple exception I think it is going well also.

Larry Gibson

[leftiye]

We all should study felix and Geargnashers last few posts. They contain a sliding scale so-to-speak concerning how a set pressure can create different velocities with (due to) different twists. This in itself when inverted says that the pressure needed to reach a given velocity will be much higher for a tight twist than it will when a slow twist rate is present (because the tighter twist requires more energy to attain velocity AND accelerate the boolit). Not to mention a few perks thrown in concerning burning curve for the slow twist. FWIW, this explains a possible (and not controvertable) prediction for virtually all of the phenomena that occur vis a vis RPM theory. Not saying RPM theory isn't right exactly, but it is a major problemo due to this to know what is actually causing the seen results.

[Larry Gibson]

Ah leftiye

Once again referring to others? Could I ask if you have conducted and tests of various twists using the same claiber? If so could you please pontificate on the results? We would all like to see them, if available.

Also, if I me be so bold to ask, have you or gear actually measured pressures to determine if there is actually a significant increase in pressure with a faster twist? Unfortunately several of you are going on the assumption that a mere change, make that increase, in twist creates a significantly higher pressure. Had gear bother to read the ballistics book I mentioned he should read he would find on page 134 the correct answer. Reading closly what felix also say there are numerous things in the barrel that influence pressure; heigth of the lands, width of the lands, number of lands, etc. other than just the twist. In the ballistics book (and most other in depth ballistic books or manuals) you will find that the difference in velocity between a fast tiwst and a slow twist alone accounts for a minimal 1/4%. The pressure difference is about 1%. To quote from the book; "The conclusion was that moderate changes in twist create such a small change in pressure they can be ignored." Now that comes from ballisticians who conducted an extensive test for a major manufacturer under strict guidelines. So which is correct; ballisticians who conducted extensive test to determine the answer or Gear's pontifications (based on any tests?) here?

You see, I have measured the pressures of .308W cartridges in 10, 12 and 14" twists. I have also measured the pressures in 7, 9, 12 and 14' .223s. And I'll be darned if I can find a real increase in pressure due to twist alone. So leftiye, if you have conducted same or with other cartridges using various twists could you relate your findings?

I have conducted numerous tests to determine the "to know what is actually causing the seen results." The results are always the same; as we eliminated "all of the phenomena" we continue to find RPM to be the determining factor. That is unless you, leftiye or perhaps Gear, have test results that prove otherwise?

You shall see the results of a further test conducted today very shortly. Stay tuned.......

Larry Gibson

[geargnasher]

Ah Ha,,,now I get it,,,,it's a Game!

Game objective,,, pressure management and accuracy. Game rules,,,,All components of the game, can be changed by the individual player at any time. Winning is achieved by obtaining acceptable accuracy.

I like to think of it as a game, the objective being what ever you set it to be based upon your wants, needs, tools, and ability.

My approach varies based upon what I'm trying to do, and what the most important objective is, be it dependable accuracy, maximum killing power, light recoil, being able to shoot long strings without cleaning the action, maximum economy, you get the idea. Sometimes the objective requires higher velocities than is the norm for cast, for example making a 300-yard elk load for a .30-06.

When one begins to take a rifle load with cast boolits beyond the 16-grains-of-2400-at 1500 fps arena, challenges arise. A LARGE percentage of these challenges are centered around doing one thing: The launch. Getting the relatively delicate, soft cast boolit out of the case, through the leade, successfully engraved, accelerated down the barrel, and clear of the muzzle in such a way that it flies straight becomes more and more difficult as velocity increases. The launch, what I think most of us agree is the process of getting the boolit from the case to the point that it's completely supported by the barrel, or about the first inch in most guns, is the most difficult to do well. The launch is critical to jacketed bullet accuracy as well.

As we increase pressures to achive more velocity we find that imperfections in boolit fit, chamber neck clearance, case length, concentricity, etc. begin to rear their ugly heads by, essentially, allowing the boolit to get a crooked start in the bore, which deforms it. Deformed boolits don't fly as well or as consitently as perfect ones, and the higher the forward velocity, the more these defects become apparent in the way the boolit flies. So you have several compounding factors: As pressure is increased to get more velocity, it's more difficult to launch a boolit that will fly straight when clear of the barrel. At a certain point this really starts to show up on a target by making the groups larger. If is sounds like I'm paraphrasing many of Larry's statements, I am. Anyone who's ventured off into the realm of HV cast boolit shooting knows all about this, and can easily discover and correct the common causes of poor launch/poor accuracy by using benchrest case prep techniques, carefully cast and culled castings, optimizing powder burn rate, charge, lube, amount of lube alloy composition and temper and a myriad of other minutia. Still, there is a point in the velocity ladder with each gun where it gets VERY difficult to maintain "decent" accuracy, and all the hubbub is about differing ideas of WHY that is, and in some threads (not this one), what to do about it if you want to go faster.

Larry has discovered through years of testing that a relationship between boolit rotational velocity and peak accuracy window appears to exist. He's declared many times why he thinks this occurs, so I won't waste time repeating it here. Generally I agree with him that this phenom exists, where I disagree on a few points is what's causing it to occur. I find too many exceptions and too many false links in the chain of reasoning to just say it's a law instead of a theory. I'd love to say he's right and that's the way it is and be done with it, but there's a lot more to it than that.

The "more to it" part is that many people here pretty much ignore RPM when loading, and often find excellent results well beyond the ideal range of RPM that Larry suggests. Like so many things in shooting, there are exceptions to most any rule or theory. I'm trying to shoot better, faster, and I want to know what's causing this "RPM threshold" and how to fix it. Larry and I disagree on some major points regarding this cause, and I feel that his explanations for the exceptions to his theory aren't sufficient. I'm trying to get to the bottom cause(s) of this so I can fix it, and some of the things Larry keeps saying are causing it don't compute with my experiences and those of others. SO, lets go over some:

First, I don't think a nose slumping off-center is the cause of the "RPM Threshold". The "threshold" might be due to imbalance of the boolit, might not be, but either way it isn't the nose. Boolit noses can and do slump off center with annoying frequency, but it's easy enough to prevent if you get your alloy and powder right. Most nose slump is at the part that doesn't normally touch the rifling, the part from the point to where the ogive touches the lands. My recent foray into paper patching was like turning on a light in a dark room. I learned that one can patch a bore-riding boolit from the scraper groove back, let the nose ride the lands like normal, and even cut most of the tail off, and shoot it to jacketed velocities with jacketed accuracy, zero leading, and not a lot of special care need be given to case prep. The kicker is that all that can be done with, literally, the same boolit from the same batch of alloy that failed a thousand FPS earlier with lube and a gas check. If this doesn't prove anything else to anyone else, it will still indicate to me that nose slump isn't what caused the accuracy of that boolit to fail, since as much as the front HALF of the patched boolit is still the same as the unpatched one, there is zero paper anywhere near the nose to add support, and the patch made all the difference in performance. It also makes me wonder if the gas check is failing as well, helping to cause the loss of accuracy at a certain point, since it can be left off as long as the driving bands are wrapped in paper and performance still throttled-up another 30% in a lot of instances. My point is that while nose slump can and will cause inaccuracy, it's easy to prevent and most of the time it isn't causing MY high-velocity shooting to experience accuracy decay beyond the points Larry has observed with his theory. As to what other parts of the boolit are becoming damaged during launch, before launch, after launch or any other time to cause the "RPM theshold" once the boolit is in flight, I can't say, but I'm pretty sure it's not the nose.

Second, I disagree with the assessment that excessive rotational velocity is the cause of the threshold. It may be more a matter of rhetoric or semantics than anyting, but to me, if there is any relationship at all, RPM is a way to determine or vaguely predict the effect of whatever is causing the threshold. Like I said about rpm being a "yardstick", or a system of calculating and measuring the effect of what's causing the groups to have an accuracy window, above and below which they typically, but not always shoot worse. I believe that there are some other factor at work, or a combination of things causing boolits to print bigger groups. The factors of external ballistics including boolit deformation, balance, gyroscopic stability, and aerodynamics seem to be just about the only factors involved with group size assuming they are launched identically. Here is where I'm trying to find SOLUTIONS instead of LIMITS or THRESHOLDS, because I might want to be able to reach out and smack Bambi at 300 yards , and I don't want to have to spend the money to rebarrel one of my rifles in a 14-twist to do it when I've seen it and done it before with a ten-twist. Others seek and find solutions to overcoming this threshold because they want to win competitions with stock military rifles that are dimensionally terrible for shooting cast, especially with the twist rates. There are ways to do this, I think I did it before with more dumb luck than anything, and those who know "techniques" to whizzing by the "RPM threshold" aren't sharing much about how they do it, or even what exactly it is that they're correcting to gain excellent accuracy well beyond Larry's observed ideal accuracy window. Veral Smith is one who's sharing for a price, but I don't think he has all the answers, either. I'd love to know more about what causes the theshold so I can extend it.

Third and last, if boolit imbalance/deformation combined with excessive rpm are all that's involved with the accuracy threshold, then it should only require eliminating the imperfections to make the boolit shoot straight. Why is it so difficult to do so? I think it's more complicated than Larry describes, not only a matter of launching a perfect boolit, but of achieving a perfect launch as well. I sure don't think it's overstabilization or any of that rubbish simply due to the fact of what a j-word or a pp can do. Maybe it has to do with the forces involved with spinning the boolit through the rifling, as discussed earlier, and THAT is why it's so hard to make a perfect boolit shoot, or one that at least SHOULD be getting launched into the bore initially almost perfectly.

Anyway, like I said, I'm in this discussion not to prove a limiting theory, but to find what causes it so I can find ways to fix it.

Gear

[Nrut]

Anyway, like I said, I'm in this discussion not to prove a limiting theory, but to find what causes it so I can find ways to fix it.
Gear
-----------------------------------------------------------------------------
Excellent post Gear..
I think that is why most of us are here.

Larry,
Thanks for answering my question about your slow twist barrel..

[leftiye]

Ah Larry, Once again flying in the face of physics? Does it absorb energy to rotate a boolit? Go ahead, try to say no! Does it take more energy to spin a boolit 130,000 rpm or 190,000 rpm? - And we haven't even mentioned the losses to friction yet. Do you think the friction loss is greater or less for a one in 10 twist versus a one in 16 twist? Do you think it takes no energy?

These are inescapable (- to all but you, who only have to deny them). I.E. if your machinery says the 180 grain 30 caliber fired through a one in 10 twist barrel goes equally fast as the same boolit same load etc., SAME pressure achieves when fired through a 1 in 16 twist barrel, then there's something else going on, the type of powder used favors the higher drag of the 1 in 10, or something else. Actually it is impossible, all things being equal, the higher drag in the one in 10 barrel will either produce lower velocity or higher pressures or both. Remember, Isaac Newton is waiting for you on the other side.

And for heaven's sake Larry, avoid at all costs examining the effects that that pressure when applied to the rear edges of the grooves in the boolit (leading edges of the lands on the boolit) has in multiplying pressure (I'd guess that most of the drag in a boolit's travel down a barrel occurs right there - probly greater than that of being fired in a smoothbore) has in creating heat. Though boolits generally may not melt during transiting the barrel, do you think those leading edges don't at least soften? Consider also that when swaged into the rifling their hardness dropped already to that of pure lead. This may be exactly where the ogre in high velocity accuracy hides. AND the interchangeability of rpms for pressure describes just the same results that your RPM theory predicts also. Still.

[303Guy]

Excellent post, Gear. Very interesting.

Most interesting about the bore-ride with the naked bore-ride section.

[Nrut]

Excellent post, Gear. Very interesting.

Most interesting about the bore-ride with the naked bore-ride section.

I noticed that also 303Guy..
I think Gear is trying to "red herring" the Common Wealth team for the next PP CastBoolit match!

The bugger!...:p

[geargnasher]

Ah leftiye

Once again referring to others? Could I ask if you have conducted and tests of various twists using the same claiber? If so could you please pontificate on the results? We would all like to see them, if available.

Also, if I me be so bold to ask, have you or gear actually measured pressures to determine if there is actually a significant increase in pressure with a faster twist? Unfortunately several of you are going on the assumption that a mere change, make that increase, in twist creates a significantly higher pressure. Had gear bother to read the ballistics book I mentioned he should read he would find on page 134 the correct answer. Reading closly what felix also say there are numerous things in the barrel that influence pressure; heigth of the lands, width of the lands, number of lands, etc. other than just the twist. In the ballistics book (and most other in depth ballistic books or manuals) you will find that the difference in velocity between a fast tiwst and a slow twist alone accounts for a minimal 1/4%. The pressure difference is about 1%. To quote from the book; "The conclusion was that moderate changes in twist create such a small change in pressure they can be ignored." Now that comes from ballisticians who conducted an extensive test for a major manufacturer under strict guidelines. So which is correct; ballisticians who conducted extensive test to determine the answer or Gear's pontifications (based on any tests?) here?

You see, I have measured the pressures of .308W cartridges in 10, 12 and 14" twists. I have also measured the pressures in 7, 9, 12 and 14' .223s. And I'll be darned if I can find a real increase in pressure due to twist alone. So leftiye, if you have conducted same or with other cartridges using various twists could you relate your findings?

I have conducted numerous tests to determine the "to know what is actually causing the seen results." The results are always the same; as we eliminated "all of the phenomena" we continue to find RPM to be the determining factor. That is unless you, leftiye or perhaps Gear, have test results that prove otherwise?

You shall see the results of a further test conducted today very shortly. Stay tuned.......

Larry Gibson

Come on Larry, lighten up, this isn't the Inquisition.

But I do have an inquiring mind, and I'm trying to figure out how if you and the ballisticians say twist has virtually no effect on velocity or pressure, why do you think twist affects accurate velocity so much that you would call it the "determining factor"?

Gear

[geargnasher]

I noticed that also 303Guy..
I think Gear is trying to "red herring" the Common Wealth team for the next PP CastBoolit match!

The bugger!...:p

[smilie=1:.....:mrgreen:


Larry gave me an idea, so I actually went to Wikipedia and looked up "logical fallacies". I took an elective course in college called "Introduction to Logic" as a philosophy credit, but all I remember was solving logic problems using Modis Ponens, Modis Tolens, etc, and the girl who sat in front of me always smelled really good! Anyway, I found this on Wikipedia at the top of the page:

"In informal logic and rhetoric, a fallacy is usually incorrect argumentation in reasoning resulting in a misconception or presumption. By accident or design, fallacies may exploit emotional triggers in the listener or interlocutor (e.g. appeal to emotion), or take advantage of social relationships between people (e.g. argument from authority). Fallacious arguments are often structured using rhetorical patterns that obscure any logical argument."

I think this thread is a textbook example of the above, no?

Gear

[Larry Gibson]

Well I’ve recovered enough from pneumonia and the acute bronchitis that has had me down the last 4 weeks to spend a decent few hours at the range. I still was a little shaky and had problems controlling my breathing but I only really called one shot in numerous 10 shot test strings. I had loaded up the Palma load with the 311466 at 2600 fps for testing in the Palma rifle with a 20” 14” twist barrel, the M70 Target rifle with heavy 26” 12” twist barrel and the reference rifle with 24” 10” twist barrel. All loads were the same in well fire formed and match prepped NS’d cases for each rifle. The load was 49 gr of AA4350 under the AC’d 311466 cast of 60/40 lino/pb. The bullets have been well aged and have a BHN of 16 – 18. They are sized at .311 and Hornady GCs are used with Javelina lube.

So I shot 10 shot strings of the same load out of each rifle at 100 yards chronographing the load. I also pressure tested the load in the Palma rifle. I then shot 10 shot strings at 200 yards to determine whether group dispersion was linear or non linear. I use 10 shot strings because that is industry standard for tests. As I mentioned to DrB in his thread a 5 shot string is not statistically significant for confidence in a load. This is well documented throughout the industry. In the tests there is a good example of how random selection and random shot dispersion can lead you to erroneous conclusions with just 5 shot test strings, more on that later.

This is going to be a long post with several photo’s and scanned groups so I may have to break it up in several posts. We shall see on that.

Lets take the .308W Palma rifle first; Note on the Oehler m43 data printout that the velocity is 2585 fps (velocity in the Standard Atmosphere Ballistics portion as the M43 correct the velocity from the screen velocity to the muzzle) . Note the average psi is 38,300. It was cooler today during the test at 58 degrees so the velocity dropped a bit below my previous reporting of 2600 fps with 40,000 psi which was recorded at 75 degrees. Sheeesh….only 2585 fps at 38,300 psi….what can I say……

You’ll see the 10 shot group pasted on the data sheet also. It measures 1.54” for the 10 shot group at 100 yards, basically the 1.5 moa I previously reported also. That is the atypical 10 shot group I can fire from this rifle at 100 yards. There is no leading and the groups will hover at 1.5 moa whether it is the 1st 10 shot string or the 10th 10 shot string….that is also without cleaning the barrel between strings. Also note the uniformity of the load; the ES is 52 fps with a proportional SD of 16 fps. The psi ES is only 1,900 psi which is also very good. Looking at the pressure traces we also see they are very uniform from pressure rise to muzzle exit (the little black hash mark).

Looking at the 200 yard 10 shot test string on the SR1 target I fired the bottom 4 shots in the 10 ring and then moved the scope up 1 moa. I then fired 5 X’s and one 10 for a score of 100-5 X. Had I the proper zero I would have fired a 100-9X. Adjusted group size taking into account the 1 moa sight change shows the group to be 3.15”. Taking the 1.54 moa group at 100 yards we find the dispersion of group size between 100 yards and 200 yards to be almost perfectly linear.

The RPM of this load in this rifle today is 133,019 obviously under the RPM threshold for this load in this 14” twist rifle. Note the psi of 38,300 is considerably over the 20 – 22,800 psi that lee’s chart says should be the “limit’ for this 16 – 18 BHN bullet. I was somewhat taken aback by 45 2.1s admonition that psi was the limiting factor considering his many posts pontificating the use of softer alloys, particularly 50/50 WW/pb, for use at high velocity. Perhaps he does not realize that high velocity does not come without higher pressures. Here again with this test using the softer 16 -18 BHN bullet we see that pressure (38,300 psi) is not a limit with the softer alloy.

The attainment of 1.5 moa 10 shot groups at 200 yards is easily obtain by using a correct alloy in a correctly designed bullet for the job such as the 311466 or the LBT bullet Bass Ackwards uses. Using a slow burning powder that gives consistent ignition and is at 95 – 105% loading density also is a key. Other than that there was no secret machinations used other than standard casting and loading techniques. The bullets were not weight sorted but only visually inspected for defects. The lube was Javelina and it performs very well at this velocity range. Note the lube “stars” on the ends of all three barrels. GCs were standard Hornady .30 cals and were not annealed or any other such. As mentioned cases were match prepped, well fired formed and NS’d in a Redding bushing die to give .002 neck tension on the .311 sized bullets.

The accuracy with this load in this rifle is reproducible at any time. It does not depend on the alignment of the moon and stars or any other such magic or witchcraft. I’ll be glad to demonstrate this to anyone at any time.

[Larry Gibson]

Now let’s take a look at the same load in the M70 target rifle with a 26” heavy 12” twist barrel. This rifle is very accurate (Schneider barrel) an will put this 311466 into moa or sub moa when below it’s RPM threshold. So let’s see how the Palma load (remember we’re talking 38,300 psi and high velocity) fares.

The Oehler M43 data sheet shows us the load is running at 2534 fps with an ES of 55 fps and an SD of 17 fps. That is pretty close to the same as in the Palma rifle. The Palma rifle’s barrel is 27.5” which accounts for the slightly lower velocity in the M70. Obviously the internal ballistics are as good as in the Palma rifle with consistent ignition. However, when we look at the M70 100 yard 10 shot test target we begin to see some accuracy problems. We see the one obvious flyer at 11 o’clock and one other probable one at 2 o’clock with the 3 o’clock one being a probable flyer also.

As this is the same load as used in the Palma rifle and the velocity is as it should be the pressure is pretty close to the same 38,300 psi as the two rifles always has similar psi with the same load when I measured pressures in the M70. The RPM is 152,040 at 2534 fps in this 12” twist barrel. Knowing the accuracy potential of this M70 rifle I suspect this load at this velocity is on the ragged edge of the RPM threshold. That is what those pesky little flyers are telling us. I tried to point this out to DrB on his thread but what I was saying has apparently fallen on deaf ears. In this case though a 10 shot test string at 200 yards will tell the tale. If the 200 yard group size is the linear to the 2.15 100 yard group then this load has not exceeded the RPM threshold. So let’s take a look at the 200 yard 10 shot test group.

The 200 yard test group does indeed tell the tale. We find 8 shots right at the linear group expansion size. Problem is we also have two flyers (same as we had 2 flyers in the 100 yard test group) that actually make the 200 yard group a 6.25” group. That is quite non linear. My suspicions that this load in this 12” twist barrel is on the ragged edge of the RPM threshold is correct as 2 shots obviously exceeded the threshold and went off on a tangent or a helical spiral out of the group in a non linear fashion. Remember, this is the same load, i.e. the same pressure so what is the culprit? The only difference is the higher RPM in this 12” twist rifle.

[Larry Gibson]

Now lets look at the 10” twist reference barrel with this same load. This is a pressure reference barrel made to minimum specs, chambered to minimum specs with maximum lands. It consistently gives 5 – 7,000 psi higher psi and higher fps than any other commercial .308W barrel I’ve tested. It’s psi reading are consistent with Federal and Winchesters psi readings of their .308W ammunition from their pressure test guns. As we see that is also the case here with the standard load for the Palma rifle. In this test barrel of 24” (2 and 3 ½” shorter that the other two barrels) the velocity is 2568 fps and the psi measures at 46,800. Also consistent with other tests the ES and SD are not quite as good at 64 fps and 23 fps, still not bad though for a 10 shot string.

The RPM for this load in this 10” test barrel was 184,970. On the picture you see both the 100 yard group Circled at the bottom and the 200 yard group which pretty much cover the whole page. This barrel is capable of moa 10 shot accuracy when the RPM is below the RPM threshold. The 10 shot test group at 100 yards is 3.78”. In the center we find a nice cluster of 5 shots that went into 1.4”. Had I been using 5 shot groups and randomly selected those 5 shots I could, like some, go around claiming “eureka”, I can shoot cast bullets at 2550+ fps in less than 1 ½ moa. You have to admit we do see that quite a bit, even on this thread. That is the problem, regardless of what some say, with 5 shot groups. They are just not a large enough sample to give ‘confidence’ that that group size is correct. This is a good example why ballisticians say a minimum of seven shots is needed and the industry/SAAMI standard is 10 shot test strings/groups.

Obviously from the 2 flyers left and the 3 flyers to the right there are some issues. Is it RPM and has the bullets, or some of them either gone off on a complete tangent or has some of the begun to spiral in a helix? The answer to that lies on the 200 yard target. There are 2 very wide flyers, low left and low right, that obviously have gone off completely on tangents to the line of depart/flight. Then look at the other 8 shots…..is that the “donut” gear was hypothesizing about? Sure looks like one. I’ve not seen one that pronounced before so perhaps they could “donut”. The group is a little over 10”, obviously a non linear group expansion from the 100 yard group.

[Larry Gibson]

Granted there is a little more pressure with this load in the reference pressure test barrel but that was expected. Then at 38 – 46,000 psi the pressure in all three rifles is well above what the psi limit for a cast bullet of this BHN that pundits claim.

Why then the really good accuracy with the Palma Rifle and the still good 8 out of 10 accurate shots at both 100 and 200 yards with the M70?

Why then the poor accuracy at both 100 and 200 yards? Why the complete linear group expansion from 100 to 200 yards with the 14” twist Palma?

Why then the 8 out of 10 shot linear group at 200 yards with the M70? Why then the 2 flyers from the M70 into a non linear group expansion?

Why then the total non linear expansion couple with poor accuracy with the 10” twist reference test barreled rifle?

The load is the same in all 3 rifles. The velocities of all 3 rifles are within 49 fps of each other. The pressure is very close to the same in all 3 rifles. The rifles are all capable of moa or better accuracy with cast bullets (jacketed also). So then what is the cause of the loss of accuracy between the 3 rifles? Is there an RPM threshold? Are we seeing the RPM threshold evidenced here here with this load at different RPMs? Pretty hard to deny it doesn't exist considering the only real difference between the 3 rifles shooting the same load is the RPM. The Palma rifle with the 14" twist at 133,000 RPM is 1.5 moa accurate at both 100 and 200 yards. The group expansion is perfectly linear between 100 and 200 yards. The M70 with the 12” twist barrel at 152,000 RPM is on the ragged edge of the RPM threshold and the 2 flyers in both the 100 yard and the 200 yard groups have pushed over the RPM threshold going off on a tangent. The reference pressure test barreled rifle with the 10” twist barrel at 184,000 RPM shows 50% flyers at 100 yards, 2 flyers going off on tangents at 200 yards, non linear expansion between the 100 and 200 yard groups, a possible “donut” effect with 8 shots at 200 yards possibly due to the helical spiral caused by the centrifugal force on unbalanced bullets over a certain RPM and this load in this rifle has obviously exceeded the RPM threshold for this load in this 10” twist rifle.

Now some may choose not to believe. They will make excuses as to why they don’t believe the obvious. They choose to ignore the science of ballistics. Their hypothesis and pontifications are loud and long. I read them, I try to explain, I quote from ballistic science, I point out industry standards and the reasons for it, mostly to no avail with some. Yet I ask but one simple thing; prove your objections that the RPM threshold is not real. They do not. Have any of them showed us 10 shot 1 1/2 moa groups at 100 and 200 yards with cast bullets at 2585 – 2600+ fps out of 10” or faster twist barrels? Have any of them measured the pressures they say are the culprit? Have any of them demonstrated any first hand proof? No, not a one. Several of them have tried with 10” twist ‘06s and not suceeded. Show us your success at 2500 – 2600+ fps with cast bullets in those 10” twist ‘06s, yes show us those 1 1/2 or less moa groups at 200 yards running 2500 - 2600+fps.

Do I claim to be able to shoot cast bullets at 2600+ fps with 1.5 moa accuracy at 100 and 200 yards with a 10” twist rifle of any caliber? No, I don’t but I have learned to shoot that 1.5 moa accuracy with 10 shot groups out to 300 yards (farthest tested). How you say? Well go back and reread this post, the answer is obvious.

Those who choose to believe the evidence presented will and those who’ve already made up their minds against won’t believe. That’s ok, it’s their loss. Does it matter if there is an RPM threshold or not? If all you want to do is shoot a cheap fun cast bullet load at 1500 – 1900 fps it isn’t going to matter. However, if you want to up the performance in velocity and/or terminal performance at longer range through higher velocity then knowing what the RPM threshold is, how it happens and what causes it will help you understand better how to mitigate it as much as possible to a higher velcocity/RPM. By mitigating the causes and pushing the RPM threshold up you can push cast bullets at higher velocities, within reason, even in faster twist rifles.

So I say to Nrut; the answer is obvious;

simply control the RPM by using a slower twist barrel,

use a bullet of the correct design,
use an alloy that is strong enough yet malleable to setback evenly during acceleration,
use a slow burning powder that gives consistent ignition and is at 95 – 105% loading density,
match prep the fire formed cases,
NS for .002 - .003” neck tension on the bullet,
Use a good soft lube like Javelina,
size the bullets to fit the throat,
do not seat the GC below the case neck,

Other than the above there is not a big secret to it. The trick is to either control the RPM And load so that the bullet does not exceed it’s own RPM threshold. If you are wanting to push cast bullets to a higher velocity in a 10 or 12” twist (or faster twist) rifle then all the above still applies. Doing everything possible to keep the bullet balanced during casting, sizing/lubing/GC’ing, loading and especially when it is fired (acceleration) so that it exits the muzzle as balance as possible is a must. The better you can do that along with the above the higher you can push the RPM threshold. Will you, I or anyone ever get 1.5 moa with a 311291 or 311284 at 2600+ fps out of a 10” twist? Probably not. But I am continually pushing the RPM threshold up in faster twist rifles with more correct bullet designs for that purpose. It’s not easy by any means but it can be done.

Larry Gibson

[Larry Gibson]

I think this thread is a textbook example of the above, no?

Not the thread but some of the posts, certainly yes.

BTW, you're not the only one who went to college. Some of us even managed to graduate:drinks:

Larry Gibson

[303Guy]

The one thing this thread is telling me is I need to spend more trigger time! There is so much to explore and so many hypothesis to test (and falacies to bust). One of the first hypothesis/fallacies is my own!:???:

Now this RPM thing ..... ? It does make sense in so far as muzzle velocity on its own doesn't seem to explain things but bring twist rate into it and a 'constant' is formed which Larry calls the RPM threshold. It does make sense - the faster the twist the lower the 'velocity threshold' becomes and vise versa. But the question being asked is why. It's apparently not the centrifugal forces acting on the boolit that cause it to distort in flight although that can happen, it seems. But that makes the RPM hypothesis real. (I think).

Here's a test that might shed some light. A bore-ride nosed boolit versus a full length engrave boolit. This is only possible in a gun that has a long tapered throat that allows rifling engagement over the full length of the taper. I happen to have one such rifle that so far seems to like big fat paper patched boolits. I've only ever put paper patched boolits through it but I'm sure I could make a mould for it.

The theory here is that the longer rifling bearing surface would have less 'shear' and be able to tolerate higher angular acceleration and thus push up the RPM threshold.

(I want to know more about the naked bore-ride section boolit. Too many folks have had success with it to be ignored).

[runfiverun]

the one question i ain't heard yet.....
why is it easier to shoot the slow twist to a higher velocity and maintain accuracy???
is it the "easier on the boolit to engage and hold the rifling" part, while not using excess energy to accelerate the boolit forward?
i'm in this camp.....
we know fit of the throat is first.
we all know protecting the boolit is a prime consideration, especially the base.
gently accellerating the boolit along then dropping muzzle pressure for a good blast free launch is necessary.
but keeping the edges tough to hold the rifling has to be right up there.....

even pp boolits need to get harder as velocity increases think on that some.

[Larry Gibson]

geargnasher

But I do have an inquiring mind, and I'm trying to figure out how if you and the ballisticians say twist has virtually no effect on velocity or pressure, why do you think twist affects accurate velocity so much that you would call it the "determining factor"?

"twist affects accurate velocity"

Not sure what you're talking about. However, twist having a negligeable affect on pressure and velocity has nothing to do with the centrifugal force of higher RPM acting on the imbalances of a cast bullet. I've absolutely no idea how you fathom, given you claim to know so much about physics, that it does. I also haven't any idea how you fathom "a nose slumping off-center is the cause of the "RPM Threshold". The nose slumping off center unbalances the bullet. The high RPM at a certain point while the unbalanced bullet is in flight is what "causes" inaccuracy. That is the RPM threshold for that particular bullet. There are any number of reasons for the bullet to become unbalanced, the slumped nose is just one of them.

Here is where I'm trying to find SOLUTIONS instead of LIMITS or THRESHOLDS, because I might want to be able to reach out and smack Bambi at 300 yards , and I don't want to have to spend the money to rebarrel one of my rifles in a 14-twist to do it when I've seen it and done it before with a ten-twist.

So please "show us" your ability to thump bambi at 300 yards with a high velocity cast bullet out of your 10" twist rifle. Hey you say you've done it, so show us some 300 yard groups of say 2 moa or better at 2400 fps (I'll go easy and not ask for 2600 fps) with cast bullets. Should be easy to do as you've done it before.

I'll be patiently waiting..............

Larry Gibson

[303Guy]

Something comes to mind, a faster twist barrel might limit the velocity of the boolit by virtue of the RPM threshold. At these lower velocities and pressures, boolit slumping is more likely to be irregular than the same boolit fired to a higher velocity with higher pressure in a slower twist barrel? Might explain why it's 'easier' to get accuracy at higher velocity out of a slower twist barrel?

[geargnasher]

Not 'til you learn to be civil, Larry, which appears will be the twelfth of never.

Bye.

Gear

[DrB]

OK, as a lead in, here's a related post I made on the precedent high velocity with a NOE225107 thread...


Larry, I think some folks may have issue with some parts of the text of your often ctrl-V'ed theory and your conclusions regarding the actual RPM values, and find nothing novel at all about the idea that you can mechanically damage a bullet by too fast an acceleration (either linear or angular), too fast an RPM resulting in exceeding yield or ultimate strength of the alloy, or bullet damage through any of a host of other bullet damage mechanisms.

Doesn't seem like either the idea that defects are bad or too many rpm's can be bad are particularly novel (or interesting unless they make specific testable predictions). If we are all finding the limitations empirically by bumping up against them, and your theory (or any theory) isn't making useful predictions a priori, how is that different from having no theory at all? The utility of a theory is dictated by it's ability to make testable predictions.

Please propose a thread for further discussion on the RPM theory and I'll continue over there. I still haven't gotten your PM with a link... Again, I would prefer that this thread not be a rehash of a debate it sounds like has been going on for years. It probably would be of more utility to future readers if we kept the content together with where you have already posted most of it so the content isn't fragmented.

Thanks Larry for continuing the discussion over here.

So, to start out with, let me repeat, again, that I find nothing remarkable (or objectionable!) about the idea that both RPM and angular acceleration (the first and second derivatives with respect to time of bullet rotation angle) can relate to bullet accuracy. They both relate to the loading of the projectile, and ultimately strength of material constraints pertaining to either variable can be violated resulting in bullet damage.

To me, the heart of the problem with Larry's RPM Threshold Theory is that it is not disprovable with respect to any RPM threshold Larry declares it predicts. A minimum rotation rate (Greenhill's Formula) is known to pertain to bullet stability and accuracy. It essentially says, for a given density bullet, and velocity regime, bullets with a particular fineness ratio will be stable in flight when spun faster than a specified rate. You know the parameters, you calculate the rate, and you can test and map out the results. Greenhill's Formula is testable, and sure, there can be some fuzziness in borderline cases, but the transition is remarkably consistent over the supersonic flight regime for a wide range of bullet fineness ratios and twists.

Unfortunately, there is no corresponding "Gibson's Formula," or even an empirical set of values Larry has been willing to specify as subject to test to disprove his theory if incorrect. Larry hasn't calculated the yield or ultimate stress limit of a bullet with respect to RPM, or anything similar -- and his theory doesn't consider the angular acceleration limitation at all. Larry's theory suggests that the limitation is just due to angular rate (RPM) and Larry suggests various "threshold" values where he believes his constraint may become active.

Let me offer an example... what matters from a scientific standpoint with regard to utility of a theory is whether the theory is capable of making testable predictions (and is subject to falsification as a consequence). So, Larry had made some predictions about what the RPM "threshold" would be for a 22 caliber projectile, namely, that it would be in the range of 120,000 rpm to 140,000 rpm. That's a prediction and should be subject to falsification, right?

Here's my pertinent data. If the below is difficult to view as sized for you, please right click, save the image off and open it with an image viewer of your choice. Sorry for any inconvenience. It should be of sufficient resolution when zoomed.

http://castboolits.gunloads.com/imagehosting/154544e40f422e0b1f.png

So, in the above figure are marked Larry's two previously stated RPM threshold values for RPM of a 22 caliber projectile. You can see that all of the current results exceed the thresholds, and display a negative correlation of group size with RPM, with the smallest group sizes provided at the highest RPMs. Now, no one should interpret the above correlation of increasing RPM with decreasing group size to imply causation in the sense that increasing RPM is decreasing group size. There are numerous other factors at play here -- different rifles, different velocities, different bullets, different alloys, primers, etc. etc. etc. Some of you will find it interesting that the test points above were for bullets: none of which were weighed and culled; some of which had gas check shanks exceeding the gas check ID; and some of which had mould half offsets of .002-.003 along the bullet axis resulting in bullets oversize in length by that amount on one side (and still the largest group sizes were about 3.8 MOA). The one thing that is very clear is that the data cannot be interpreted to support any notion that group size increases with increasing RPM above Larry's stated threshold values.

RPM Threshold disproved? Nope. Not according to Larry. Essentially, Larry's response comes down to that the "threshold value" just depends on a whole bunch of other things most of us probably already recognize as important to bullet integrity, and a threshold value for RPM isn't a threshold in any sense you'll find in a dictionary, but rather an undefined range of values over which his RPM Theory may or may not become important. That LG Threshold 1 marked on the chart above? Well, it could be that really the RPM Threshold is at LG Threshold 2, or any other greater value anyone may happen to demonstrate after Larry suggests a lower Threshold. There's no equation for a "threshold value" as a function of caliber and other variables, and no values that can be tested that would result in the falsification of Larry's RPM Theory. As a result, no one can conduct an experiment that would disprove Larry's particular RPM Threshold Theory by exceeding any RPM thresholds Larry suggests are relevant for a particular caliber.


Okay, so that's a summary of the hard data I have and what I believe Larry's response to it thus far amounts to.

I have told Larry that one possible approach to adding some credibility to his theory does occur to me, in terms of physically demonstrating a component of his theory. His theory does appear to make a prediction that might be tested and as a result subject to confirmation or falsification:


“the bullet is unbalanced or becomes unbalance due to obturation in the bore during acceleration. The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around it's geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release. After exiting the muzzle, the geometric center will begin to revolve about the center of mass and it will depart at an angle to the bore (line of departure). At 54,000 RPM to 250,000 RPM, depending on velocity and twist, the centrifugal force can be tremendous. It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.”

Here we go, deconstruction, piecewise, to confirm I am interpreting Larry's RPM Theory as Larry intended. Larry – please don't expound upon any of these points if I've got it right, as while I mean you no offence by saying so, I really don't have time to wade through more of this than is necessary. If I've said something wrong in my parsing of your theory though, please correct it, and affirm I've got something right if I got it right. Let's try to keep this as simple as it can be and no simpler. :) If the above is so quintessentially your theory in a nutshell, let's try to keep it clean.


“the bullet is unbalanced or becomes unbalance due to obturation in the bore during acceleration. The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around it's geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release. "

Alright, so "mass center" = "center of gravity" in Larry's nomenclature, no problem. CG's are points, and points don't have directions, so I'm pretty sure Larry means that the CG departs with the velocity vector it had at the moment of release. (The bullet is also being accelerated by venting bore gases, gravity, the freestream, etc. after bullet/bore separation, but Larry's theory makes no mention of these whatsoever, and so I must assume that all of these are entirely extraneous to Larry's theory. No problem – no one is saying they don't matter, they're just irrelevant to Larry's RPM Theory and the resulting post bore departure motions of the bullet he theorizes.)

Next:

"After exiting the muzzle, the geometric center will begin to revolve about the center of mass and it will depart at an angle to the bore (line of departure). "


I understand here that Larry is saying there is a transition in rotation of the body from about a geometric axis (roughly defined by the bore centerline) to about an axis of rotation passing through the center of gravity of the projectile.

"it" in "it will depart" does mean center of mass, right, Larry? Or do you mean the geometric center?


“At 54,000 RPM to 250,000 RPM, depending on velocity and twist, the centrifugal force can be tremendous. “

Here Larry is talking about centrifugal force experienced by the bullet after the bullet has departed the bore. Correct?

Next:

"It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.”

It = "centrifugal force" caused by the rotation after departure from the bore, right?

So next let's talk about this helix part. The word helix has a meaning, so I presume Larry intended to use the word helix and in fact meant that some point of the bullet body is following a path described by a helix. Which part of the bullet Larry might be referring to is kind of important, here... and the above “RPM Theory” hasn't specifically said anything about that. Right? That's one of the questions I previously asked Larry in the prior thread – what point in particular on the bullet body is traversing the “constantly growing helix?” CG? Something else?

Okay, well, let's have some helix fun. I'll incorporate Larry's answer later.

Helices have equations something like:

x(t)=sin(t)
y(t)=cos(t)
z(t)=t

So presumably for Larry's helix he means something like:
Coordinates & variable definitions:

r == range (positive downrange)
h == altitude (positive up)
w == windage (positive right)
f == (temporal) frequency of helix rotation
ph == a constant to describe the initial angular phasing of the helix (probably can't control that if it's due to slumping!)
v == downrange velocity
t == time
R == radius of helix (R = fn(t), because the helix is "constantly growing." However, Larry's use of the word "constantly" is a little vague here. Larry could mean that the R is growing without acceleration as a function of time, and so has a form of R=b+k*t, where b and k are two constants, or, by "constantly" maybe he means the derivative dR/dt > 0 for all t > 0, which really is a very different thing.)

Notional equation of Larry's helix:

r= v(t)*t
h=R(t)*cos(2*pi*f*t+ph)
w=R(t)*sin(2*pi*f*t+ph)

So Larry, what I previously asked you for on the prior thread, is for you to just fill in a couple of small details regarding the above helix. I've tried to sketch in the general outlines based on the words in your theory, so if you can just provide the following, we'll procede:

1) pick a load/rifle combination that you are confident typifies your "RPM threshold" MOA vs. range degradation. Whatever you like, but be sure to pick one you are willing to rely upon as a means of falsifying your theory if what you have supposed is happening isn't really happening.
2) you say the bullet is rotating in an ever expanding helix.

a) please name the feature/point of the bullet that is travelling in the helix (do you mean the center of gravity?)
b) define (or at least bound) the frequency of the helix f for your answer from 1... or you could provide the spatial period of the helix (=v/f, the distance travelled down range for one revolution around the helix). It sounds as though with your description of the center of form rotating about the center of gravity you are saying that the spatial period of the helix is about equal to the twist rate of the barrel (call it TR), and so f = v/TR. So if the above is right, you can just enter your estimated muzzle velocity in inches per second divided by the twist rate of your barrel.
3) provide at least a rough estimate of R at the downrange target (say at 200 yards for your answer from 1... wherever this RPM theory is at play). The magnitude of R presumably is what is causing your groups to widen, so you should be able to use the unexpected difference in group size from close in to 200 yards to approximate the magnitude of R at 200 yards, right?

Once we've got a rough guess from your theory about these parameters, I think I may have a way for you to cheaply experimentally confirm or discount your theory. Given how nebulous your RPM threshold values are, it seems the most plausible route to me to lending credence to your theory, in that you are describing a characteristic of the motion of the projectile that perhaps is particular to your theory.

Best regards,
DrB

[Larry Gibson]

303guy

" It's apparently not the centrifugal forces acting on the boolit that cause it to distort in flight although that can happen, it seems. But that makes the RPM hypothesis real. (I think).

Here's a test that might shed some light. A bore-ride nosed boolit versus a full length engrave boolit. This is only possible in a gun that has a long tapered throat that allows rifling engagement over the full length of the taper."

No, when the RPM threshold happens to a cast bullet the centrifugal force is not strong enough to "distort" the bullet in flight. The "distoriton" happens in casting, sizing, loading and accelleration. The RPM?centrifugal force, at the RPM threshold, act upon those "distortions" that are cause before and during muzzle exit, not during flight.

Go for it with that test. It will show you what I mean by a "properly designed cast bullet for the task".

Larry Gibson

[Larry Gibson]

runfiverun

"the one question i ain't heard yet.....
why is it easier to shoot the slow twist to a higher velocity and maintain accuracy???"

I answered that question in the above test. The answer is simply that the slower twist keep the RPM lower, at any given velocity. In the case of the test compare the RPMs of each twist. The 14" twist barrel, at basically the same velocity for all 3 rifles, kept the bullet under its RPM threshold. The 12" twists RPM had the bullet on the ragged edge of the RPM threshold. The 10" twist was obviously "over the top" of the RPM threshold.

With slower twist barrels you can manage the RPM by keeping them under the RPM threshold. Simple as that.

Larry Gibson

[Iron Mike Golf]

Larry, this is meant to be a helpful suggestion and not a rock-throwing incident.

Many of us, including me, measure our groups by taking the two widest hits, measuring the distance, and then subtracting one bullet diameter to get the center-to-center distance. I think that's fine for a first-pass evaluation of loads and is in fact adeqaute for most of our purposes in load development, gun tuning, and so on.

But your line of investigation may be better served by approaching group size the same way you approach velocity measurement with your chrony: mean, standard deviation, extreme spread. Measuring group size in our "standard" way is like only measuring extreme spread. I think getting the mean and SD data is really important when you are trying to discover transitional or boundary regimes and behaviors.

Just a couple of pennies.

[Larry Gibson]

DrB

“Larry – please don't expound upon any of these points if I've got it right, as while I mean you no offence by saying so, I really don't have time to wade through more of this than is necessary. If I've said something wrong in my parsing of your theory though, please correct it

Be glad to do it; 1st of your entire chart. The problem with it is your data. The sample size of your groups is too small. Industry standard is 7 – 10 shot groups which are statistically valid sample sizes. Five shot groups are not. That is not from me but from all the ballisticians who do it for a living. Say what you might in fancy words that really don’t say anything but that is a fact; you need to increases your sample size for validity. Second all your groups are plagued with pesky little flyers. Bullshops are too. That is an obvious indicator that your loads are already outside, i.e. over the RPM threshold for those components in your rifle. It is why they are outside "LG Threshold 1 and LG Trheshold 2". Did you not bother to take note of my above posted test and what the flyers indicate, apparently not. Drop your load down below the RPM threshold as I suggested you do (you blew me off because you already predisposed your choice in this matter) and work up through and then past the RPM threshold. When you find the best accuracy and then where that accuracy begins to get worse is where the RPM threshold is for your components and rifle. I would bet that on a new chart it will fall between “LG Threshold 1 and LG threshold 2”.

You also seem to forget that the quoted description of what the RPM does is not from me nor is it my theory. It is straight from ballistics manuals and books. Perhaps you are contending that they are all wrong and somehow, based on a few non valid 5 shot groups, you’ve got it all right? If so then you’ve really got to be kidding……thus your criticism of me regarding the CGs is really a criticism of all the ballisticians isn't it? That's pretty bold talk! Larry’s “theory” does contain the "centers" and I have mentioned the center of form, center of rotation and center of gravity in just about every explanation of the RPM threshold. Your whole expose’ line by line is again, not what Larry is saying but what is in all ballistic manuals and books. It is what the real experts say and prove. Obviously you’ve not really studied in ballistics or you would know that. The quotation from those ballistic books and manual is correct, you’re assumptions and attempts to discredit it are wrong, pretty much that simple.

BTW; it is not a point on the bullet that goes into the helix, it is the bullet itself. Nice try to prove a bumble bee can’t fly with the formulas. I suggest if you want to study and use real formulas for ballistics use you consult a ballistics manual, as I mentioned to gear; UNDERSTANDING FIREARM BALLISTICS, by Robert A. Rinker is a good one for the beginner. It has lots of real and useful ballistic formulas for you to have fun with. You will also find the quotation you attribute erroneously to “Larry” in that book.

I’ll continue with the last of your post in the next post.

Larry Gibson

[Iron Mike Golf]

Some more thought, regarding testing:

1. Has anyone ever measured the center of mass of bullets and compared home cast to factory jacketed?

2. How about testing using a lathe-turned solid bullet? I am thinking those might be the most dimensionally uniform and homogenous bullets available.

3. How about altering a mold to purposely cast a bullet with the center of mass not on geometric center (is that the centroid?). I was thinking of beagling just one outer edge of the blocks.

[Larry Gibson]

DrB (cont'd)

"So Larry, what I previously asked you for on the prior thread, is for you to just fill in a couple of small details regarding the above helix. I've tried to sketch in the general outlines based on the words in your theory, so if you can just provide the following, we'll procede:

1) pick a load/rifle combination that you are confident typifies your "RPM threshold" MOA vs. range degradation. Whatever you like, but be sure to pick one you are willing to rely upon as a means of falsifying your theory if what you have supposed is happening isn't really happening."

I picked the load and used it the test posted above with3 different twist rifles. The load was giving basically the same velocity and pressure. The only difference was the RPM.

"2) you say the bullet is rotating in an ever expanding helix. "

I said, quoting from ballistic manuals, when the bullet passes the RPM threshold the centrifugal force acting on the imbalance of the bullet (center of gravity not coinciding with the center of form or center of spin) which causes the bullet to begin a helical spiral or to depart on a tangent (it may do one or the other depending on the amount of centrifugal force and the amount of imbalance). The helical spiral does increase in a non linear fashion as the range increases. The amount (diameter of the spiral) at any given range is also dependant on the amount of centrifugal force and the amount of imbalance.

"a) please name the feature/point of the bullet that is travelling in the helix (do you mean the center of gravity?)"

It is the bullet that is traveling in this particular helix. Do not confuse this helix with the helix caused by initial wobble, yaw and perhaps nutations on muzzle exit of the bullet. That action is most common noted when the bullet “goes to sleep” with in a couple hundred yards. They are both helix’s but they are from 2 different actions.

"b) define (or at least bound) the frequency of the helix f for your answer from 1... or you could provide the spatial period of the helix (=v/f, the distance travelled down range for one revolution around the helix). It sounds as though with your description of the center of form rotating about the center of gravity you are saying that the spatial period of the helix is about equal to the twist rate of the barrel (call it TR), and so f = v/TR. So if the above is right, you can just enter your estimated muzzle velocity in inches per second divided by the twist rate of your barrel."

Here again you are making the erroneous assumption the helical spiral rotates around the path of light some certain definable number of rotations in a specified range. Once again a study of ballistics would tell you that the helical spiral may not make a complete rotation around the line of flight, even at maximum range. Again the diameter of the spiral and the rotation time of the spiral are dependant on the amount of centrifugal force (that is how high the RPM is when this action starts) and the amount of imbalance in the bullet (how off center the GC is from the COF and the COS). As to the “frequency” (assuming the number of helical spirals around the line of flight?) if we are talking a range of 200 yards and an RPM barely over the threshold and the bullet imbalance is small then the arc of the helical spiral will be very small as will the diameter. However, if the RPM is considerably over the RPM threshold and the imbalance is still small the arc and diameter will be larger. If the RPM is way over the RPM threshold and the imbalance in the bullet is larger the arc will be larger as will the diameter of the spiral at the given 200 yards. The bullet may also not spiral, if the centrifugal force is high enough and/or the bullet imbalance is large enough, but may go off on a tangent.

"3) provide at least a rough estimate of R at the downrange target (say at 200 yards for your answer from 1... wherever this RPM theory is at play). The magnitude of R presumably is what is causing your groups to widen, so you should be able to use the unexpected difference in group size from close in to 200 yards to approximate the magnitude of R at 200 yards, right?"

The adverse action, either helical spiral or off on a tangent, begins at complete muzzle exit of the bullet and continues in a non linear dispersion rate as range increases only if the centrifugal force is acting on the bullet imbalances. A perfectly balance bullet in flight is not affected. “Magnitude of R”; you continue to want absolutes but anyone of scientific bent is well aware there are many things that are not “absolute”. The “magnitude of R” will be dependent on the amount of centrifugal force based on the amount of RPM and the amount of imbalance in the bullet. Isn’t this the 3rd or 4th time we’ve been over this. Please study ballistics so we don’t have to go over this again.

"Once we've got a rough guess from your theory about these parameters, I think I may have a way for you to cheaply experimentally confirm or discount your theory. Given how nebulous your RPM threshold values are, it seems the most plausible route to me to lending credence to your theory, in that you are describing a characteristic of the motion of the projectile that perhaps is particular to your theory. "

Some friendly advice; that kind of “nebulous” language is fitting in an academia environment but on this forum it hurts most peoples heads. Just because many of us don’t talk or us language like that you might not want make another erroneous assumption that we are not educated, many of us are.

Have you looked and studied the results of the test I posted above? If so then it really does or at least should answer all your questions. However, if you still have reasonable questions that perhaps your test will answer then, by all means, state what the test is. I also suggest again you conduct the test I suggested as it is well within the means you have and not very expensive at all, might just be fun for you too!

Larry Gibson

[Larry Gibson]

Iron Mike Golf

Appreciate that. However I learned long ago not to worship the SD god. It comes up misleading too many times; As an example; I recently, just this week, chronographed two different loads (10 shot strings). The SD for both was the same but there was a 38 fps diference in the ES! We have to understand that the SD is a theroetical value of only how unifrom the velocity spread might be. The ES on the other hand are real high and low velocities and can tell us if there will be vertical dispersin at long ranges. On target the SD gives us a theoretical +/- of where 90+% of the shots should hit. Measuring the ES of the widest bullet holes tells us what the bullet actually did on target. BTW; when chronographing (I use Oehler chronographs BTW) I always compare the SD to the ES to make sure they fall within acceptable proportion to each other. If they do, all other things being equal, accuracy will be good. If the SD is low but not proportional to the SD I have found vertical stringing to be the most common problem associated with that.

There are numerous ways (the military uses mean radii for example) to actually measure group size, I was going to use mean radii but then realized I would have had to go into a whole other explanation of what it is. Using the ES is the most common method for measuring group size and most easily understood by everyone. That's why I used ES.

Thanks for the input as it provides mor food for thought on this thread.

Larry Gibson

[leftiye]

"A Real Test" Uh Oh another "experiment"

So you go out with ammo that has already been tested and was in stock on your shelves, which you already know exactly what it will do, and you produce a data set that says what you want to hear with guns also previously tested with those loads. BTW this is exactly what you did in your first "experiment". That time you used a defectively fitting boolit (bore rider nose too small) which you knew previously how it would behave.

Back then you knew that best accuracy could only be attained at about 1600 fps, and that accuracy went to -south above that, and that 2100fps is insane. Now you're At 40,000psi and 2600 fps - which was the fabled "High Velocity" (deep booming voice) back then that only Bass could do. The RPM Barrier was at 120,000 rpm or less, now it's a threshold and it's at 140,000 or more rpm. Since you've corrected yourself, why don't you stand corrected? (it's like waiting for the end of the world)

Back then it couldn't be done. Now YOU are the on telling us all how to do it as pertains to high velocity.

Rehashing the same old oatmeal over and over with a few "adjustments" thrown in every so often doesn't prove anything. That data does fit your expected phenomena as per your model. As has been said over and over however you can't connect the dots:
First - you cannot prove that internally occurring deformation and other factors aren't the operant factors.
second - Nor is there any reason that rpm must take a hand for the targeted phenomena to occur.
Thirdly - We're all STILL waiting with baited breath for you to put down the Shaman's rattle and put down in black and white how rpm alone does anything but make a boolit wobble.
Many other thangs DO make a boolit wobble. Without air to plane upon the boolit isn't going anywhere.

[Larry Gibson]

leftiye

You have tests of your own that prove otherwise or is this just your usual pontifications?

Would be nice to see something you've actual done with a rifle and cast bullets at any velocity other than you just pounding away on a keyboard. Please add something to this discussion useful instead of just criticising and complaining.

Thank you

Larry Gibson

[leftiye]

Ad hominem argument Larry. More correctly, no argument at all. (just ignore those facts that are problematical) YOU are the one who has to defend your theory, until you do I for one am not convinced.

[Iron Mike Golf]

Larry,

I think that for the purposes of validating yloour theory, mean radius and SD of that will show effects faster than just ES. The flyers could be bullets with gross non-uniformities of density. But what about the "average" bullet? ES doesn't tell us about the behavior of the majority of the bullets fired.

From a practical[/b] standpoint, ES is extremely useful. Since we don't have a handy, inexpensive way to test the bullets before firing for uniform density, we can't cull those. Using ES for load development tells us where even the worst case falls.

Personally, I have decided to use mean radius for my own load development. I realized I was using it [i]qualitatively already. I was looking at sets of groups and ranking them, even though the ES numbers were very close. A cloverleaf of 4 with a 5th an inch off the side was better than a group with all 5 more or less evenly distributed in the sam ES diameter circle.

[felix]

Larry, most of your language has dealt with what I will call "steady state" statistics. The literature you have been referencing appears to be the same in that regard, including the 1/4 percent to 1 percent pressure variation between different twists. I am most interested in the "transients" of the variables we have under discussion. For example, your chrono picture with the pressure curves do show a distinct disturbance in pressure at the very beginning of the individual traces. For a gun to be "accurate" those traces should be identical in MINUTE detail. Also, you will note that all "math" exhibited so far in the thread assumes steady state responses, which cannot explain these pressure disturbances.

The best literature I have seen that relates to this RPM business deals with turbine design parameters and the transient relationships therein. That would require using Laplace transforms or the use of Taylor series to break the calculus into algebraic terminology. No one here is interested in this rigorous treatment to their understanding.

Turbines deal with "known" ambients because of their total enclosures. Projectiles are released in all kinds of enclosures from cartridge to target. There is no way math can come into play with any predictability whatsoever. That's why statisticians came into being....to help in these "futuristic" endeavors.

... felix

[BABore]

Leftiye pretty much nailed it here. Rpm's are not the problem here unless they're not suficient for stability. High rpm's have no effect on a boolit that passes the muzzle with no internal or external distorsion. Several here have posted groups shot at high rpm's that far exceeded the so called threshold. 357Max for instance posted several. How were they explained away? Congratulations in some cases and basically calling the shooter a liar in others. Well it is possible to shoot HV cast boolits. It's not he rpm's that are the problem. They just amplify a poorly fit, poorly cast, poorly alloyed, poorly lubed, or poorly launched boolit. If you correct those issues the effects of high rpm's goes away. Time would be much better spent discussing the issues of attaining a perfect boolit and launch than to blather on about how you can't shoot HV well because of a condition that you can only control by getting a different twist rate. Many just don't have that option and have to work with what they have.

Which brings up an interesting question that has bugged me since this all came up. Larry, You have pointed out ad nausm that you know what it takes to do it right with boolit fit and such. You were not satisfied with a 30 caliber, 1 in 10 twist, so you got a 1 in 12 twist. Then a 1 in 14 twist. Why haven't you also had a custom mold built for a perfect fit for them or even one of them? Wouldn't that be a great start to defeating your rpm monster? I ask this because that's exactly what I did when I first started casting. I was advised by a few kind board members on how to attain higher velocity and I went and did it. The 3rd mold I purchased was a custom. I was not alone in this either. We all were able to get HV accuracy by correcting the real problems.

[BABore]

Larry, most of your language has dealt with what I will call "steady state" statistics. The literature you have been referencing appears to be the same in that regard, including the 1/4 percent to 1 percent pressure variation between different twists. I am most interested in the "transients" of the variables we have under discussion. For example, your chrono picture with the pressure curves do show a distinct disturbance in pressure at the very beginning of the individual traces. For a gun to be "accurate" those traces should be identical in MINUTE detail. Also, you will note that all "math" exhibited so far in the thread assumes steady state responses, which cannot explain these pressure disturbances.

The best literature I have seen that relates to this RPM business deals with turbine design parameters and the transient relationships therein. That would require using Laplace transforms or the use of Taylor series to break the calculus into algebraic terminology. No one here is interested in this rigorous treatment to their understanding.

Turbines deal with "known" ambients because of their total enclosures. Projectiles are released in all kinds of enclosures from cartridge to target. There is no way math can come into play with any predictability whatsoever. That's why statisticians came into being....to help in these "futuristic" endeavors.

... felix

Felix,

Are you getting at the exit pressure differences of the guns used and how those differences can disrupt the launch as the boolit exits the muzzle.

[leftiye]

Amen.

[felix]

Yes, warranting the Amen exclamation. ... felix

Not only exiting, but initializing and everywhere in between as well. ... felix

We are actually interested in the displacement of all objects within the system, from gun to target. Pressure is only one of the variables. ... felix

[Larry Gibson]

Ad hominem argument Larry. More correctly, no argument at all. (just ignore those facts that are problematical) YOU are the one who has to defend your theory, until you do I for one am not convinced.

That's your usual excuse. The problem is i have defended and proven the RPM threhsold is real. It is now up to you, if you disagree, to prove it isn't. You have possesion of the football, show us some actual tests that disprove it. A 10 shot 1.5 moa group at 200 yards running 2600+ fps with any cast bullet out of a 10" twist '06 perhaps? "o6s aren't to hard to find......

Let me reiterate; you seem to forget that both Bass and I got 2 moa up through 2200 fps with that 311291 in 10" twist '06s. He did it in one, I did it in three. We both did it using slow burning powders and accuracy enhancing loading techniques. We pushed the RPM threshold for that bullet in 10" twist barrels up and then guess what happened, we lost accuracy because with those componants and loading techique we hit the new higher RPM threshold and accuracy went south.

Yes, of course, I knw what would happen during the test. However, I did not have the load "on the shelf". That load had been developed and shot in the Palma 14" twist rifle only. I really had no idea exactly how it would perform. Yes I could predict the 12" twist M70 and the 10" twist test barrel would be over the RPM threshold but I did not know. The m70's accuracy still surprised me but then it really shouldn't have considering the bullet design and slow powder used. Granted the poor accuracy out of the 10" twist test barrel was very predictable. Predicting the RPM threshold will happen andpredicitn the exact RPM it will happen at are two different things. We can predict the first but not the second regardless of what DrB seems to think or want.

The simple fact remains; 1.5 moa at both 100 and 200 yards with linear dispersion between the groups simply by controlling the RPM. Apparently my consistently demonstrating that really upsets you. That is unfortunate. I would really like to see, as I'm sure we all would, your high velocity/high RPM cast bullet groups?

Larry Gibson

[leftiye]

No excuse Larry - you foisted a fallacy off on us. Misdirected the focus of the issue. You do this more than a lot.

Suggestion that should be adhered to in this three gun scenario - all three guns have barrels made at the same time by the same barrel maker (and by a good barrel maker), maybe star or air gauged. Same length, same chambering exactly. Boolit made from a mold that is ideal for that chambering, and optimal design for high velicity so weaker gun doesn't just fall through the cracks. Three different twists. There's no guessing how much difference exists between a Palma match barrel and a factory Winchester barrel. And, don't forget - same make and model rifle. Then maybe you've got a chance to claim maybe some validity (it's as close as you can get, but not perfect even then). Oh, with a load developed in 1 in 10 twist barrel, not the 1 in 14 barrel.

So you're saying that in the tests you and Bass ran, in addition to being spun too fast the loads were simply shot too fast - and accuracy went to - south. Still with the boolit with the undersize bore riding section? Simply by controlling the rpm? - and how many other ways could it have been accomplished? So, wherever accuracy disappears it is the rpm factor, not the boolit made of swaged shot that disintegrates?

[Larry Gibson]

felix

"For example, your chrono picture with the pressure curves do show a distinct disturbance in pressure at the very beginning of the individual traces. For a gun to be "accurate" those traces should be identical in MINUTE detail. "

First understand how the psi is measured with a strain gauge; there must be enough pressure exerted to "stress/expand" the barrel steel over the chamber for the strain gauge to get a measurement. It takes a certain amount of pressure to expand the cases, sealing the chamber before pressure can even be exerted on the chamber walls. If you look in the middle column you will find "Offset Press" at 7,000 psi. This is the "average" psi required to expand the "average" FL sized or new brass cartridge case before it can exert any pressure on the chamber walls. The begining horizontal line represents that time period from primer ignition to when the psi is enough for the barrel steel to expand/stress and pressure measurement to begin with the strain gauge.

With FL sized or new cases the intital horizontal line will be quite straight as you expect. However, in this test all the cases in all three rifles were well fire formed and NS'd. Thus the "distinct disturbances you observe are the psi under the 7,000 "Offset Press" caused by the well fitting fire formed cases already expanded and touching the cahmber walls allowing earlier stress/expansion of the cases against the chamber walls and the strain gauge picking it up and measuring it. That's what those little squibbles are.

1 1/2 moa at 200 yards with a cast bullet at 2600 fps and 38,300 psi is not "accurate"? Excuse me if I just don't buy that one.

"Turbines deal with "known" ambients because of their total enclosures. Projectiles are released in all kinds of enclosures from cartridge to target. There is no way math can come into play with any predictability whatsoever. That's why statisticians came into being....to help in these "futuristic" endeavors."

Now I will most certainly buy into that one:-D

Larry Gibson

[Larry Gibson]

BABore

Leftiye pretty much nailed it here. Rpm's are not the problem here unless they're not suficient for stability. Not correct, the test I posted and all those flyers that plague you with the Hornet, Bullsop with his cartridg and DrB with his K-Hornet tell the tale.High rpm's have no effect on a boolit that passes the muzzle with no internal or external distorsion. Absolutely correct. I have, numerous times including a couple in this thread, stated that a balanced bullet on exit from the muzzle will not be adversely affected by the RPM. so what's the point if we are agreeing? Several here have posted groups shot at high rpm's that far exceeded the so called threshold. 357Max for instance posted several. How were they explained away? Congratulations in some cases and basically calling the shooter a liar in others. Well it is possible to shoot HV cast boolits. Yes it certainly is possible to shoot cast bullets at high velocity, no doubt there. The trick is to do it accurately at not only high velcocity but also at high RPM. You shoot your bullets at high velocity from your Hornet into 3 moa(?). The 100 yard goups exhibit flyers that are probably caused because of the higher RPM and the load is exceeding its RPM threshold. AT lower velocity/RPM you rifle is quite capable of much better accuracy with those same cast bullets, isn't it?. You prove it yourself; lower the RPM = better accuracy. Raise the RPM = worse accuracy with those pesky little flyers. That's also what is plaguing Bullshop and DrB. Conversely, in the test posted, I shoot a cast bullet at high velocity and with excellent accuracy at 100 and 200 yards simply by lowering the RPM. With the same load when the RPM is upped in the 12 and 10" twist rifles the accuracy goes because the load is exceeding the RPM threshold at those same velocities but higher RPM. Hard to argue with the facts. It's not he rpm's that are the problem. They just amplify a poorly fit, poorly cast, poorly alloyed, poorly lubed, or poorly launched boolit. If you correct those issues the effects of high rpm's goes away. Isn't that exactly what I've been saying all along? Appears were are saying the same thing.Time would be much better spent discussing the issues of attaining a perfect boolit and launch than to blather on about how you can't shoot HV well because of a condition that you can only control by getting a different twist rate. The purpose of this thread was to help others understand the why of what was happening with the RPM threshold. I think I have demonstrated that why very well. Once the why is understood then we can better do things to mitigate the problem and push the RPM threshold higher. As I reiterated to leftiye; Bass and I both did it with a, admitingly, ill fitting 311291 in 10" twist '06s. One does not have to get a slower twist barrel to push the RPM threshol upwards. We just have to lauch a more balanced bullet so the RPM won't act on it until a higher RPM/velocity is reached. I have alredy listed numerous things to Nrut in an above post to mitigate and push the RPM threshold upwards. You obviously didn't take note of that. We still must realize that with fast twist barrels there is pretty much only so much we can do. At the psi required for high velocity the cast bullet will still undergo a lot of stres during acceleration. However, why don't you start another thread on the how to mitigat the effects of RPM on unbalanced bullets since the why has been so aptly demonstrated on this thread? Indeed, that would be a good thread.Many just don't have that option and have to work with what they have.Very true, that's why you need to understand the why so you can move on to the how.

Which brings up an interesting question that has bugged me since this all came up. Larry, You have pointed out ad nausm that you know what it takes to do it right with boolit fit and such. You were not satisfied with a 30 caliber, 1 in 10 twist, so you got a 1 in 12 twist. Then a 1 in 14 twist. Why haven't you also had a custom mold built for a perfect fit for them or even one of them? Well, in truth, I am an old High power shooter so I had the M70 Target and the Palma rifle for those games using jacketed bullets. I didn't get them to shoot cast bullets. However, I don't shoot much high power any more (age and tired eyes do catch up to us) so I shoot a lot more cast bullets in those rifles for fun. BTW I also have 7, 8, 9, 12 and 14" twist .223s. I also have 12, 14 and 16" .22 Hornets and ahave also shot cast in several other cartridges with different twist barrels. The results are always the same as with the test i posted above. Exceed the RPM theshold and accuracy goes south. I have used the "custom mould" LBT bullets that bass uses. They are very good for .308W and '06s. However I have not found them to be any better than the 311466 I am using. Have you an idea for a better bullet?Wouldn't that be a great start to defeating your rpm monster? Been trying for years to "defeat the RPM monster". Every test with, even those with multiple twist barrels just further proves the "monster" is real and alive. I ask this because that's exactly what I did when I first started casting. I was advised by a few kind board members on how to attain higher velocity and I went and did it. The 3rd mold I purchased was a custom. I was not alone in this either. We all were able to get HV accuracy by correcting the real problems.I'm sure you either have or have access to a 10" twist .308W or a '06. You also amke some very fine custom moulds. How about showing us some 10 shot groups of 1.5 moa at 100 and 200 yards with any cast bullet running 2600 fps? I sure would be glad to see them and be proved wrong. I'm sure a few others here would really like to see such 1.5 moa groups at that velocity out of 10" twist .308Ws or 10" twist '06s. How about it?

Larry Gibson

[felix]

Larry, 7000 units for case rupture. Prolly another 7,000 units for boolit engraving. It is beginning to add up. At least we are beginning to think transients. ... felix

[Larry Gibson]

Leftiye

Suggestion that should be adhered to in this three gun scenario - all three guns have barrels made at the same time by the same barrel maker (and by a good barrel maker), maybe star or air gauged. Same length, same chambering exactly. Boolit made from a mold that is ideal for that chambering, and optimal design for high velicity so weaker gun doesn't just fall through the cracks. Three different twists.

Well why don't you just do that then to disprove what I have done. I'll make you a wager; my 3 rifles against your 3 test rifles that you come out with the same end result. That is assuming you also get some means of measuring the pressure. How about it, time to put up?

So you're saying that in the tests you and Bass ran, in addition to being spun too fast the loads were simply shot too fast - and accuracy went to - south. Still with the boolit with the undersize bore riding section? Simply by controlling the rpm? - and how many other ways could it have been accomplished? So, wherever accuracy disappears it is the rpm factor, not the boolit made of swaged shot that disintegrates?

Seems to be the problem leftiye, you're not quite grasping what is said. I did not say Bass and I shot those 311291s accurately to 2200 fps "simply by controlling the RPM". I said we used '06s with 10" twists and used slow burning powders and advanced loading techniques. RPM was in the 159,000 range when accuracy went south for both of us. It was using the slow burning powders and the advanced loading techniques that enabled the both of us to push the RPM threshold from 1900 fps (it shoots very nicely in 10" twists at or below that velocity with fast or medium burning powders and regular loading techniques, that is its RPM threshold with those) to 2200 fps and 159,000+ RPM which is how high we pushed its RPM threshold. Neither of us were able to push it higher with any reasonable accuracy. The 311291 is really not a very good design for any higher velocity/RPM with accuracy. Again, a cast bullet of proper design for high velocity/RPM will push the RPM threshold even higher. As and example both Bas and i pushed the LBT bullet to almost 2400 fps with consistent 2 moa accuracy at 100 and 200 yards in the same 10" twist '06s.

I've no idea what you are talking about referring to "the boolit made of swaged shot that disintegrates" as I'm not talking disintegrating bullets. Is that pertinant to the topic of this thread?

Larry Gibson

[Larry Gibson]

Larry, 7000 units for case rupture. Prolly another 7,000 units for boolit engraving. It is beginning to add up. At least we are beginning to think transients. ... felix

I don't think that 7,000 psi is "case rupture" ", I understand it to be case expansion. I suppose if unrestrained by the chamber that might be enough to rupture the case though.....interesting.......

Larry Gibson

[leftiye]

Wiggle wiggle Larry. There's a problem with YOUR test. Thas not my problem. It's yours.

[Larry Gibson]

Wiggle wiggle Larry. There's a problem with YOUR test. Thas not my problem. It's yours.

The problem is leftiye, you think I just dreamed this up. I've been studying and testing this for years. The results are always the same. I didn't fall off the turnup truck yesterday. Besides rifles that have come and gone I have five '06s with 10" twsit barrels all different. Given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have four .308Ws with 10" twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three .308Ws with 12" twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three MNs in 7.62x54R all with the same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have four 7.65 Argentines all with the same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three 8mm M98s all with same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have four 6.5 Swedes allwith the same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three .223s all with 12" twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.


There's probably more but 30 rifles is a sufficient sample size, the point is in all of those barrels (30 of them with just a quick count) there is not one single exception that might even indicate that a different barrel with different shaped lands/grooves of the same cartridge with the same twist makes one iota of difference. They all hit the RPM threshold with the same cast bullet and load (in the given cartridge with the same twist) at the same velocity/RPM. Now unless you, or any one else who might agree with you, have some empirical data from your own testing instead of hypothetical pontifications that shows otherwise I'm going to say the difference in barrels makes little difference. The test showed quite clearly the adverse affect on accuracy that increasing the RPM did to the same load fired in all three rifles.

I think it was Einstien that said something like; insanity is doing the same thing over and over again and expecting different results.

We can do the same thing (test for the RPM threshold) just like I did and the results are always the same. Problem is some do keep expecting different results. Why don't you test for yourself and see. That would answer your own question and I and others would really like to see something you've actually done with regards to shooting cast bulets at high velocity in any rifle with a fast twist regardless of the cartridge.

It's not "wiggle, wiggle" if you've walked the walk and then talk the talk. Have you walked the walk?

Larry Gibson

[leftiye]

Geez! You poor kid! Only nine hundred and sixty 06s. Must be awful.


P.S. You forgot wiggled the wiggle. Still your problem.

[onceabull]

allsameee---Minus only that Legend in his own mind ("starmetal") to carry water for the naysayers... Onceabull

[onesonek]

"It's not the rpm's that are the problem. They just amplify a poorly fit, poorly cast, poorly alloyed, poorly lubed, or poorly launched boolit. If you correct those issues the effects of high rpm's goes away."

You know Bruce,,,,,, it's not fair to inject common sense.

[leftiye]

Larry, Someone here who I respect asked me to not push you over the edge too much. But I seem to remember you paraphrasing Einstein concerning the definition of psychosis. I do believe you were insinuating that I had that problem. I.E. doing the same behavior over and over and expecting results to vary. So, maybe one more observation.


Quote - "I have three .308Ws with 12" twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three MNs in 7.62x54R all with the same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have four 7.65 Argentines all with the same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three 8mm M98s all with same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have four 6.5 Swedes allwith the same twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.

I have three .223s all with 12" twist barrels all different makes, given the same cast bullet and load they all hit the RPM threshold at the same velocity/RPM.


There's probably more but 30 rifles is a sufficient sample size" - unquote Larry Gibson

BTW your writeups don't prove the RPM theory, they just yield predictable results. Prediction is nice, but it doesn't necessarily encompass causation. The fact that you try to attribute causation to RPM theory doesn't succeed, you cannot make the link between results and your theory. You have not demonstrated that yet. And yes, you do it over and over and expect it to prove your theory. And instead of answering challenges you "pontificate" the same old mouthwash over and over. Now what was that Einstein said? Curious that you would try to lay that on me.

[Larry Gibson]

Leftiye

And you have quanitative test results to prove the RPM threshold false? Kindly show us your tests and data?

As to Einstien's saying; you missed the point, I expect the same results over and over again as they prove the RPM threshold. It is you who keep hoping for a different result to disprove it. Is there something positive you could contribute here, whether it proves me right or wrong, it would be much appreciated?

Larry Gibson

[Larry Gibson]

"It's not the rpm's that are the problem. They just amplify a poorly fit, poorly cast, poorly alloyed, poorly lubed, or poorly launched boolit. If you correct those issues the effects of high rpm's goes away."

You know Bruce,,,,,, it's not fair to inject common sense.

I believe that is just what I also have said numerous times. However, how many here can "correct those issues" with a cast bullet at 2600 fps and 38,300 psi out of a 10" twist barrel? Not many, or at least we've not seen any 10 shot groups at 100 and 200 yards attesting to it as requested. Much easier simply to control the RPM as I've apply demonstrated. Yes, a new barrel is expensive but so is a custom mould. How much you're willing to spend depends on whether you really want to shoot cast bullets at high velocity with any degree of accuracy.

Not to long ago a member posted a thread wanting advise on building and '06 so he could shoot cast at 2600 fps with moa accuracy. I advised him since he was building the rifle to use a 14" twist barrel of 26" length or longer. He berated me and said I was wrong and said many others had shot cast bullets at moa at 2600 fps out of 10" twist barrels including himself (sound familiar?). He didn't build the rifle but instead bough a M70 '06 with a 10' twist. I assume he gave the 2600 fps a try but last we read on that thread he was content down in the 1800 - 1900 fps range with that rifle as that's where he was getting the best accuracy. Well guess just how many RPM are generated in a 10" twist at 1800 - 1900 fps? Figure it out and you see it's under the RPM threshold that is "predictable". Funny how that works.

I suggest anyone wanting to shoot cast bullets at high velocity build a rifle to do so. I suggest a 14" twist for .30 cal in particular, especially the .308W or the '06. From my test you can see what can easily be done with cast bullets at 2600 fps simply by controlling the RPM.

However, if you want to shoot high velocity at 2600 fps with your 10" twist '06, .308W, 7.62x54R, 7.65 Mauser, 8mm Mauser or any other cartridge with a barrel twist close to 10" you should understand the implications and consequences of pushing that cast bullet over the RPM threshold with the componants and load used in that faster twist. We can do everything right in casting and loading to ensure the bullet is balanced but when it accelerates from standstill to 2600 fps in 24 - 30" of barrel the bullet is under very high inertial stresses. Those stresses are what most often make it unbalanced regardless of the care we take in casting and loading. Subject that unbalanced bullet to high RPM and we see the inaccuracy that results if it exceeds its RPM threshold as I've demonstrated.

Larry Gibson

[leftiye]

Yup, he said it again.

Occam's razor Larry. We don't need to have RPM theory to explain the results. Other models do it just as well. You have predictability, not causality. We have seen reasonable accuracy at 3000, 3300, and 3600 fps. Wait a while Larry. you'll probly see linearity tests to 200 yards. How much would one need to slow down Bullshop's 225107 to get good accuracy do you think? Or DrB's? (which got more accurate as speed increased, BTW) The boolits do go that fast, accuracy is surely down the road. What has been done doesn't qualify as bad ya know.

[Larry Gibson]

Leftiye

And you have quanitative test results to prove the RPM threshold false? Kindly show us your tests and data?

Larry Gibson

[leftiye]

Is there an echo in here? Kindly argue conscientiously Larry. Kindly also answer points made to you (and before distorting same). Kindly do not manufacture data. Kindly stop insulting everyone who disagrees with you.

Can you prove that god is not a 50 gal. drum orbiting Uranus? The null hypothesis can be proven, but that which does not exist cannot be disproven. So it is with the rpm theory. (Though probly for a different reason).

[Junior1942]

Drums are 55 gallon.

I suggest looking at the velocity/twist listings for various matches in the back of *The Fouling Shot*. Those group-size listings and scores were shot in front of witnesses. Larry won't be surprised at what he reads. Others here will.

[onesonek]

I believe that is just what I also have said numerous times.

Then why does it so often seem, that you argue against someone even trying

However, how many here can "correct those issues" with a cast bullet at 2600 fps and 38,300 psi out of a 10" twist barrel?

I believe that question really should be,,, how many wish to do so, with their own wants needs and goals in mind


Not many
Maybe, maybe not. But to lump everybody together, and make such a statement is a rather arrogant assumption


, or at least we've
you mean I don't you

not seen any 10 shot groups at 100 and 200 yards attesting to it as requested.
Put in such way, could be construed as insulting to one's integrity.
Perhaps, as long as you have suggested a book, maybe one could suggest to you reading,
Dale Carnegie's book "How to Win Friends and Influence People"
I know people here and eleswhere, whom don't post results for 2 reasons. One, they have nothing they care to prove, but only to themselves. Two, to save themselves, the disparagement, or out right being called liar's.

Much easier simply to control the RPM as I've apply demonstrated.
This conveys, it silly for someone to try something different, and think outside Your Box

Yes, a new barrel is expensive but so is a custom mould.
Considering it all starts with the boolit first, for me at least, the mold cost is good investment. But it is far less costly place to start, in my mind. The other option is always open, if I cant reach my goals with what I have, barrel wise. If I was to do it your way, I would still start with custom mold first, but that's me. Not saying others should do likewise. They can play the game any way they wish. It's not for me to decide what is best or easiest for them.


How much you're willing to spend depends on whether you really want to shoot cast bullets at high velocity with any degree of accuracy.
This really don't deserve a rebuttal, but again implies Your Way is Best.


Not to long ago a member posted a thread wanting advise on building and '06 so he could shoot cast at 2600 fps with moa accuracy. I advised him since he was building the rifle to use a 14" twist barrel of 26" length or longer. He berated me and said I was wrong and said many others had shot cast bullets at moa at 2600 fps out of 10" twist barrels including himself (sound familiar?). He didn't build the rifle but instead bough a M70 '06 with a 10' twist. I assume he gave the 2600 fps a try but last we read on that thread he was content down in the 1800 - 1900 fps range with that rifle as that's where he was getting the best accuracy. Well guess just how many RPM are generated in a 10" twist at 1800 - 1900 fps? Figure it out and you see it's under the RPM threshold that is "predictable". Funny how that works.
Anybody that has been shooting cast, and push a particular cartridge's capability, know things can get dicey in a hurry. Simply put by BaBore, more attention to detail is needed. Just because your said individual decided not to persue it, don't mean it can't be done in other ways than yours.
And I don't see anybody claiming your methods do not work, and are without merit. Just if someone wants to go another route, even if it takes more work, or attention to the inherent details, so beit, that is their prerogative,
What's funny, is how you tend discourage if not out right disparage those that want try other ways, than your way.

I suggest anyone wanting to shoot cast bullets at high velocity build a rifle to do so. I suggest a 14" twist for .30 cal in particular, especially the .308W or the '06. From my test you can see what can easily be done with cast bullets at 2600 fps simply by controlling the RPM.
A suggestion is fine, but your persistence of,,,,my way is easier, can get get annoying. Maybe you need to consider also, some are limited to working with what they have. And something easy is not an issue for them. After all, experimenting and shooting is part of the fun in getting there.

However, if you want to shoot high velocity at 2600 fps with your 10" twist '06, .308W, 7.62x54R, 7.65 Mauser, 8mm Mauser or any other cartridge with a barrel twist close to 10" you should understand the implications and consequences
According to you.
of pushing that cast bullet over the RPM threshold with the componants and load used in that faster twist. We can do everything right in casting and loading to ensure the bullet is balanced but when it accelerates from standstill to 2600 fps in 24 - 30" of barrel the bullet is under very high inertial stresses. Those stresses are what most often
but not necessarily always
make it unbalanced regardless of the care we Itake in casting and loading. Subject that unbalanced bullet to high RPM and we see the inaccuracy that results if it exceeds its RPM threshold as I've demonstrated.
With your practice's,,,,,,, others have shown otherwise, just by going to a slower powder than you suggest

Larry Gibson

Now obviously Larry, you have done a lot of testing, and I respect that and your findings. But I have found through the years, there is most always more ways then one to skin a cat. To the point of almost demanding other's follow your way, is akin to being stuck in a rut. However, what works for you is great, but should not limit other's to experimenting on their own. After all, experimentation and pushing the performance levels, is the heart of progress with any technology.
But it primarily goes back to the adage,,,,each to their own.
In general I think it would be a good thing if you "lighten up alil", as the repetitive and persistent nature, gets just a bit old. That's just my personal thought however, and not meant to belittle you in any way. I know you have strong beliefs in your findings. Just wish you would be a little less, of what I consider, demanding and discouraging to others.
With that, I will close with one other thought, that has had great a influence on me,,, a quote I found years ago from an unknown to me author,,,,
" life is a journey of many trails, the trail one choose's, is not as important as how one walks it"

[Larry Gibson]

I see this thread has boiled down to the very few pundits who, without comprehensive test results of their own, wish to argue withthings like "according to you, to each his own, Lighten up (does that mean ignore facts and not learn?), god is not a 50 gal. drum(?) orbiting Uranus?, I know others who have"......etc. It is thus becoming a simple arguement instead of the discussion of facts on the why RPM adversely affects accuracy at a certain point in velocity i. e. the RPM threshold. Nothing positive will come out of furthe argument, furthe r discussion yes but arguing over such as mentioned is pointless.

Those who understand the point being made here (the vast majority of readers and cast bullet shooters) have made their concurance known to me. Those who still object are certainly free to do so but it would have been more productive had they used facts and test results for their objections. Their objections not with standing, the RPM threshold has been quanitatively demonstrated.

Understanding why it happens will allow those of us who do wish to shoot cast bullets at higher velocity with accuracy in faster twist barrels that we have will be able to objective push the RPM threshold higher. Pushing the RPM threshold higher is the how that is the interesting part. We may not be able to push velocity as high in a faster twist barrel than in a slower twist barrel with the same accuracy but we can now understanding the why of it. With advanced loading techniques it will be interesting to see how future technology, perhaps like the lube Bullshop and DrB are using, will allow us to push the RPM threshold and maintain accuracy at high velocity/RPM with the common ternary alloys most of us use.

We know that with harder alloys with addtional metals like copper (as in babbit) or with PPing the RPM threshold can be pushed quite a bit higher. The adverse affects of the RPM threshold will still occur but many times with super hard alloys or PPing the velocity at which it will happen exceeds the case capacity/velocity level of the cartridge used. That is good, eh? That is the point I have come to with the 14" twist Palma rifle in .308W with ternary alloy cast bullets; case capacity is now limiting any further increase in velocity with accuracy. Using faster burning powders causes more imbalance to the bullet during acceleration and accuracy is not as good. My plan is to aquire another 14" twist barrel, or perhaps a 16" twist barrel of 28 30" length. I will cahmber it in 30-6 to pick up addtional case capacity. with such perhaps 2800 -3000 fps with 1 - 1.5 moa using ternary cast bullets may be possible?

Junior is absolutely right; I have looked at the match results and am not surprised with the scores shot nor with the twists and velocities they were shot with. The bench rest boys do indeed understand the RPM threshold and the adverse affects RPM can have on accuracy. Fortunately most here do also. I will be out of the net so to speak for a week as I'm leaving in a couple hours on an antelope hunt. It should be fun and I plan shooting lots of .44 magnum, .45 ACP (in my M98 converted) and .223s with cast bullets.

See you all next week and always good talking with you.

Larry Gibson

[onceabull]

How 20th century of you--It's common knowledge that those old guys shooting the CBA matches haven't tried anything new since 1960---all the progress with boolits is due to those innovators shooting keyboards in the cyberworld...:kidding: Onceabull

[Nrut]

How 20th century of you--It's common knowledge that those old guys shooting the CBA matches haven't tried anything new since 1960---all the progress with boolits is due to those innovators shooting keyboards in the cyberworld...:kidding: Onceabull

You miss ole Joe don't ya...:twisted: :-D

[onesonek]

"does that mean ignore facts and not learn?"

I wouldn't call it ignoring facts. Just contending that those are your facts or findings based on your loading practices. And not learn???? My God, just because someone wants to persue something other than what you say,,, the arrogance abounds once again.
Change one thing in the methodology, and it all changes. Nobody said pushing the RPM up is easier, just in all probability, possible. And even you said it's possible!!!
But then turn around and say in so many words, it's nuts to try, or telling them they are ignorant for not listening or doing , as you say.
While I respect your work on this, I also have equal respect for those willing to persue and push further!
As I see it, you are already pushing higher, the generally desired or accepted GSF of 1.5, and having good results with Your techiques and components. Actually out to 300 yds, a 1.2 GSF would be more than satisfactory. So what's to say, it can't be pushed further? Granted, finding the sweet spot may be tougher, but so what. The only difference in going to a higher rpm, (providing one employs BaBores strategy and one end up with good accuracy) which results still in a higher GSF, is the boolit will want more, to maintain the angle of launch to the bores axis, resulting in a more nose up attitude at impact, of which is little enough, to be of little consequence out to the range's being discussed. Then, what if it's somebody's want/need are just to have higher impact velocities at short to modest range, where 200 -300yds., and 1-2 moa isnt needed?
Then so what, if a 2 moa group at 100 yds, turns into a 6 moa at 200 yds. Does it really matter based on that particular need?
I think, you are assuming, that everybody has the same goals and motivation as you. Maybe so with some, and then again, maybe not with others.
And then Bench Rest, can be altogehter a different game, then say just a good hunting load. Accuracy is still the name of the game, but the criteria can be different

[leftiye]

How 20th century of you--It's common knowledge that those old guys shooting the CBA matches haven't tried anything new since 1960---all the progress with boolits is due to those innovators shooting keyboards in the cyberworld...:kidding: Onceabull

Ounceabull, Well, at least you're at least part right. (seems to be epidemic here) Them there guys are not in the least interested in high velocity may be more to the point. Nor are they guided by anything that mentions rpm.

[Pat I.]

Them there guys are not in the least interested in high velocity.

I don't know about that. I shoot my 30x47 at 2600 fps with a 165 LBT mould and another guy is shooting a 150 gr LBT bullet at 2600 fps in the 30 BR. Then there's the guy shooting 2900 fps with again a LBT bullet in a 6 PPC and a guy shooting 2400 fps with a 170 gr LBT (this is getting monotonous) in a 30 BR. Or how about the other guy shooting 3000 fps in another 6 PPC. There's more but I think you get the point and they're all chronographed with the results witnessed and scored.

Common denominator between all these examples? Slow for caliber twists just like the jacketed BR shooters use. I might be the only one to actually think about rpm when putting a gun together or working up a load but if they realize it or not the other guys are too. Or at least the shooting results are.

[felix]

Actually, it is common sense once fitted jacketed bullets are seen to shoot more accurately than the best fitted boolits out of the hopper. Especially when so much energy goes into initializing the projectile into the barrel. Imagine the force demands on twisting a boolit faster and faster without the needed long-term obturation support from behind, typically offered by the slower propellents. ... felix

[geargnasher]

Larry, "lighten up" meant relax, take a breath, and quit being so deadly serious. Insulting and belittling doesn't make for good debating, regardless of facts and data.

Gear

[Pat I.]

Actually, it is common sense once fitted jacketed bullets are seen to shoot more accurately than the best fitted boolits out of the hopper. Especially when so much energy goes into initializing the projectile into the barrel. Imagine the force demands on twisting a boolit faster and faster without the needed long-term obturation support from behind, typically offered by the slower propellents. ... felix

I'll be the first to admit I'm not the brightest bulb in the string so maybe that explains why I don't know what the heck that even means?????

[felix]

Just in support of what you have stated, Pat. ... felix

[leftiye]

Obturation would be needed to maintain seal and avoid skipping in a HV load with a tight twist. Slower twist and slow burning powder equals not deforming boolit due to further obturation and avoiding skip (and breaking seal) in the first instance by utilizing a slow twist. This arrangement also reduces the forces necessary to increase rotation during acceleration due to lesser angles of attack and due to not producing the rpm in the first place. Rpm in this case is immaterial, it is the result, not the cause.

This is a good example of the interior aspect of the "rpm" theory. Where does it say this is not the operant issue in producing velocity with accuracy?

[leftiye]

"It is thus becoming a simple arguement instead of the discussion of facts on the why RPM adversely affects accuracy at a certain point in velocity i. e. the RPM threshold." L.G.

Two simple explanations. First - it doesn't. And were not required to agree with you, nor help prove your idea. Second - It doesn't. "Certain point" Which point is that in this particular instance? Maybe 185142 rpm at 3600 fps? I'm waiting for you to try to say that these rpms and velocities are within your idea's prediction. Remember, you started at 115,200 rpms and 1600 fps. Is the next upward adjustment coming soon? The threshold is somewhere close to 115000 to 190000 rpm? Yes?

[Pat I.]

Since I made a vow to myself not to get into any RPM or Swede arguments again I think it's best to just let people think what they want no matter how much hard evidence there is contrary of their opinion.

[swheeler]

Since I made a vow to myself not to get into any RPM or Swede arguments again I think it's best to just let people think what they want no matter how much hard evidence there is contrary of their opinion.

Sounds like GOOD advice from a SMART man.:drinks:

[lwknight]

I know that you can spin a bullet fast enough to blow apart within 100 yards when you get into the 4000fps range but my 06 will shoot 216,000 rpm (3000fps w/1:10) and put round holes in dimes any time I want it at 100 yards.

OK, true its with jacketed bullets but the point is that RPM is not as much a factor as is the pressure applied to the bullet to launch it. Cast lead simply will not tolerate the same pressures that jacketed bullets will.

Think about it. Anytime you want higher velocities you have to use a hard enough alloy to hold the riflings and harder alloys are also more brittle and will not flow like plasticized softer alloys will.

Any time you want to push a cast bullet to 150,000 rpms you are also shoving the bullets tail through its nose and could even be causing internal fractures or separations in the core which will definately affect balance.

A tighter twist causes higher chamber pressures with the same load so its not fair to say " same load in 1:10 vs 1:12 because its a different pressure to start with.

Thats just my thought FWIW right or wrong.

[DrB]

Wow, Larry, true to form as always. You managed to not directly answer a single question in your initial replies, and to do so with dripping condescension. You were right not to expand on your RPM Theory and go back and crib more from your references. For you to expand upon errors you already didn't understand would have lead to you making more mistakes I would have called you on. Unlike you, who have repeatedly suggested I was making errors or lacked depth in my comprehension of ballistics without ever citing examples, I have always described anything I objected to and why. All you appear to be capable of is casting vague aspersions and condescension without substance.

Let's not forget to compare and contrast to your most recent posts the gibberish you started out with posting in your (half-dozen) pastes of your RPM Theory:
“the bullet is unbalanced or becomes unbalance due to obturation in the bore during acceleration. The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around it's geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release. After exiting the muzzle, the geometric center will begin to revolve about the center of mass and it will depart at an angle to the bore (line of departure). At 54,000 RPM to 250,000 RPM, depending on velocity and twist, the centrifugal force can be tremendous. It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.”

The above bunk is what I have a problem with, not the work of professional ballisticians -- your improvisation, Larry. I have no problem with the italicized cribbed part, and never have. If you are attributing all of the above to Rinker, then yeah Larry, Rinker is spouting bunkum (truly awful aphysical wording at the very least) and you couldn't tell the difference and quoted it repeatedly. Please do provide a page and paragraph citation, or post a copy -- I really doubt that is a verbatim quote, as no professional ballistician with a rudimentary understanding of physics would write that way (and no editor would allow the typos and redundancies). 'Fess up as to what parts are your own, or post a copy of the original text in full from the book.


UNDERSTANDING FIREARM BALLISTICS, by Robert A. Rinker is a good one for the beginner.

Yeah, I like my own professional references, Larry. I'm pretty sure Rinker would be a great big step down from re-deriving analyses from old AGARDOGRAPHs. Maybe your choice of references is the source of the problem, here. On the other hand, I would hate to impugn Rinker when I suspect it's your lack of comprehension that's at fault.

The only thing you made obvious with your initial reply is that while you've stated the bullet is flying in a helical trajectory due to centrifugal force (an impossibility), you have absolutely no idea as to the frequency of the trajectory, it's size, or how you would go about predicting them. Kind of what one would expect with a fictional helix resulting from a nonsense theory, right? :D Your answer even sounds like you are wondering if it's much of a helix at all. Which, as you probably guessed, is exactly what I was going to tell you how to demonstrate for yourself by test -- that there is no helical trajectory causing dispersion for all our high velocity cast bullet flights. The shot dispersion in Bullshop's and my own tests is entirely attributable to other factors. And in fact, the relevant (correct) portion of your theory that you cribbed doesn't result in a helical motion of the bullet post separation from the crown but a simple constant velocity crossrange drift (velocity in the plane normal to the bore axis).

You keep talking about 200 yards, but you are skirting the fact that all of Bullshop and my testing has been at 100 yards or less, and yet you have continually insisted that our results evidence the results of your theory. You can't have it both ways, Larry. Either Bullshop's good results at 100 yards and my constant MOA vs. range call into question your theory, or your theory says nothing about our results.

You cannot have a helical trajectory of a free-flying bullet without aerodynamic forces and bullet yaw, which you have never made any mention of, and occur irrespective of any RPM threshold. Conversely, the simple crossrange drift that results from an offset between the CG and geometric center at separation from the muzzle also occurs regardless of RPM, but has no possibility of resulting in a helical trajectory. While it is true that you can have strength of material related failures as a function of all the stresses imposed upon a bullet, and that these are likely to result in bullet imbalance, these are not exclusively related to RPM, and will be a STRONG function of caliber with rpm related limits decreasing with increasing caliber, the opposite of your predictions. Strength of material related failures can occur because of not only RPM, but too much angular acceleration, skid, "set-back", gas cutting, bore roughness, etc. "Obturation," or the bullet sealing the bore against gases, while solely mentioned in your theory in the context of a displacement between the CG and geometric center, in and of itself has nothing inherent to do with bullet imbalance and RPM. Aerodynamic forces due to rotation about other than the geometric axis of symmetry will cause increasing dispersion with range (as will gravity in combination with muzzle velocity SDs and wind), but has nothing to do with "centrifugal forces" or an RPM threshold (other than as related to bullet damage, which really is a "NO, DUH" isn't it). Lateral dispersion down range due to the misalignment of CG and the geometric center and the event of separation at the crown do not result in the creation of a radial force -- they result in the release of the radial force and the departure of the round from the bore with a tangential component of velocity. Again, any "helical" downrange trajectory of significance has to be due to aerodynamic forces acting on lower frequency nutation of the bullet nose. Larry, you have conflated enough different phenomenon and are just a tiny bit right and a lot wrong in enough different directions at once that I don't see how you think you have any passing understanding of this subject matter, much less judge yourself competent to remark on the qualifications of others. Are you under the impression that our dialogue so far has been of benefit to me, or your ignorant condescension other than an annoyance? It's been pretty clear to me, at least, that you've just been posturing for the benefit of others rather than engaging in any substantive dialogue on the points. You've been rude and condescending to one member after the other on this thread... frankly, I'm not seeing much redeeming virtue in your having a keyboard at all.

The more uncomprehending pronouncements on statistics and ballistics of yours I read, Larry, as contrasted to the obviously cribbed passages (so strongly contrasting to your own ctrl-v'ed theory) the more I become convinced that this whole (three year?) debacle of your RPM theory is entirely a result of your lack of reading comprehension. I think all of this could have been avoided if you simply had stuck to what others had written, distinguished between your own efforts and that of others, and attributed the work of the professionals to the professionals instead of cribbing some and improvising the rest on your own in your CTRL-V'ed "theory". Throw away all the parts of your copied franken-theory that are original but wrong (the helical trajectory absent any consideration of aerodynamic forces, the centrifugal force post bore departure, the obturation (well, not wrong but unnecessary)), and keep the part that is completely unoriginal but right (that a bullet will rotate about the geometric center while in the bore, and that the center of gravity will consequently depart the crown with a tangential velocity) and you will be back to a semblance of reality pertinent to what Bullshop and I tested (and incidentally, without a Larry RPM Theory to paste).

Despite your suggestion and your own contrary example, I don't condescendingly assume that anyone is uneducated, or that fools (even principally) reside among the uneducated. You have caused me to have doubts based on what you've written, however, and you have stated doubts about me. I propose we do a little exercise to test our respective reading comprehension of what you yourself have copied:
Tell us according to the copied (correct) part of your theory what the deviation on target of a 40 grain .224 diameter bullet is fired from a 1/14 twist rifle at 100 yards, as resulting from a .003 offset in the mould halves (resulting in the nose being that much longer and the base flat). Let's provide the answer in Minutes of Angle, and use a nominal density of lead of .4 lbs/inch^3. This scenario should sound relevant to you in the context of the recent tests.

I'm wondering if you'll even be able to start, even though the part of your theory that you copied which is correct is the part that tells you how to do it! I did the calculation from first principles, Larry -- but you go ahead and do it open book. I'll show all of my work, Larry -- please do show all of yours. Maybe one of Rinker's neat ballistic's equations will give you something to "play with."

I'll post the answer here tomorrow. I'll predict you won't even try... but will just offer more of the same condescension and personal attack. Come on Larry, put up or shut up. You want to pretend that you know anything about external ballistics as compared to incorrectly cribbing from a reference? Then demonstrate you know something about the trivial basics like conservation of momentum according to words you've been presenting in your own theory for years. When you get the answer maybe you'll be so thoughtful as to explain what it means, and why it's necessary for us to have a Larry RPM Theory in light of it?

As far as your other points, Larry:
you don't understand basic statistics well enough to argue them yourself (instead you copy what you don't understand, misapply it, and then say -- well, all the experts can't be wrong! Which is exactly the point -- they aren't Larry, you are).
you don't understand that angular acceleration increases with increasing radius and believed exactly the opposite until I corrected you.
you don't understand that a bullets trajectory may be modelled as an equation of a point in space (I thought the helix thing as a choice of trajectory as explained as resulting from RPMs & "centrifugal force" in your theory is absurdly aphysical, but it was your theory, so please don't stick me with that);
or that there is no role of "centrifugal force" in free flight "causing a bullet to fly in an ever expanding helix" (ever heard of principal axes, you know, the ones that by definition pass through the center of gravity?);
easily the most offensive of your many peccadilloes: you insist on making up your own definition of "threshold" when we all have dictionaries.

After all of the above, you are going to try to paint me as the ignorant one here? :D

Larry, I am degreed in aerospace engineering and earned a doctorate, and while I did some work for the university to pay my way, and some NASA centers over the years, I spent most of my time in industry. But no matter where I worked or how I earned a living, I have always had the honesty to concede the limitations of my knowledge when confronted by reality. I would never be caught dead going around and inventing new meanings for perfectly good words like "threshold" to try to obscure the fact that my pet predictions had failed time and again.

I think there are some pertinent things I said in the prior post that may help some of the other folks here with some of the redundant points you've just tried to make that were previously answered.


DrB
Be glad to do it; 1st of your entire chart. The problem with it is your data. The sample size of your groups is too small. Industry standard is 7 – 10 shot groups which are statistically valid sample sizes. Five shot groups are not. That is not from me but from all the ballisticians who do it for a living. Say what you might in fancy words that really don’t say anything but that is a fact; you need to increases your sample size for validity.

Here's one:





Keep in mind that while a 5 shot group is "standard" fare these days it still is not really statistcally valid. A minimal sample of 8 is with 10 being preferred to get a 90% + assurance the data is valid.

Larry, your statement is incorrect (and vague). The statistical adequacy of the population sample size is dependent upon both the nature of the population(s) and the statistical inference that is being made.

For example, here's an example of how your statement is untrue. If I wish to make the statistical inference that one population's mean was greater than another's, and the real mean value of one population was a million with a standard deviation of one, and the real mean value of a second population was one, with a standard deviation of one, and I took a sample size of three from each population, computed the mean of each, etc., are you really arguing that if I repeated the statistical test using samples of three from each population a large number of times, I wouldn't come to the correct decision more than 90% of the time (or less than 99.9999...%)? Or that the computed theoretical statistical confidence from a single test of a sample of three from each wouldn't be WAY in excess of 90% for just three samples each (I could run that number for you, but I think the answer is intuitively obvious as I've laid it out)?

There is not a fixed "right" sample size for a statistical inference. The necessary size depends on the inference and the populations being sampled... it also depends on the model.


I'm sure there are a bunch of folks here who will get the point of the above, Larry, and realize on their own that there isn't a one-size-fits all fixed sample size for every situation, every population, and every statistical inference. How many data points are required to correctly make a relative determination about the size of the means of two different populations depends: 1) on the proximity of the means; 2) the variance of the populations; and 3) the desired statistical confidence. When you start talking about linear or multiple linear regression, the number of model parameters (degrees of freedom) and geometric distribution of the points in the independent variable space also become important. It may be I am talking about something you don't comprehend, Larry, but don't you think that means you might want to listen to what I am explaining to you a little more closely?



By the way, to the gentleman who posted earlier about using standard deviations instead of group size:
I completely agree with his point. If you make the usual random normal distribution assumption, group sizes will statistically grow with increasing sample size ad infinitum... whereas estimates on the standard deviation, x and y, will converge about their true values according to the central limit theorem, and you can estimate the confidence and error of the estimates. They will also show evidence of the effects of muzzle velocity variance and wind dispersion which "group size" will combine (and this is a potentially confounding factor for falsifying your "RPM Theory" Larry as range increases).

The reason folks do it the way they do is that group size is easy to measure with a ruler, whereas calculating the standard deviation on x and y requires locating each hole, calculating means on x and y, and then calculating the respective standard deviations. In my experimental design for the hornet test I ran it with individual targets for each shot for each variant, with the order of the shots distributed to average out fouling and heating effects between the variants. Consequently I had to measure the individual shots and compute SDs, group sizes, etc.

DrB

[DrB]

Yup, he said it again.

Occam's razor Larry. We don't need to have RPM theory to explain the results. Other models do it just as well. You have predictability, not causality.


BINGO. Exactly right, except I don't think he has predictability either.... which really means, without predictability or causality Larry has nothing.

Besides which, Larry's RPM Theory says nothing about why the RPMs he cites... again, he has never posted anything to suggest he has done the least bit of theoretical physical analysis to identify limits. In contrast, the one time he's tried to say anything to me about the way it should trend theoretically as a function of caliber he got the physics absolutely backwards. The correct part of the text he just cribbed, shoot, you can even find the fluffy correct part of it on page 18 of volume 1 of a Hornady Reloading Handbook (or any high school physics text, for that matter).

[grouch]

O.K. so what should I be getting from my 1:18 to 1:12 gain twist barrel?
Grouch

[felix]

Calculate for 12 twist. Gain twist requires more attention to boolit detail and the application of pressure. ... felix

[Nrut]

Why is that Felix?
I always (guessed) the a gain twist would be better/easier to get to shoot than a standard twist for shooting cast bullets..

[felix]

Yeah, it sure does seem like it. But, in reality, it's not because the boolit sees "new" engraving all throughout the whole barrel instead of up front where the velocity at twist entry is just above zero. The shorter the full diameter of the boolit is, the more twist can be applied for the "same" amount of "twisted" damage. This relationship alone will even make a constant twist barrel shoot better. However, on the contrary, a very, very slight gain twist can be beneficial in keeping the twisting mechanism honest when making the barrel. ... felix

[KYCaster]

delete

[KYCaster]

I was about to comment on this thread when I read this:


Wow, Larry, true to form as always. You managed to not directly answer a single question in your initial replies, and to do so with dripping condescension. You were right not to expand on your RPM Theory and go back and crib more from your references. For you to expand on errors you already didn't understand would have lead to you making more mistakes I would have called you on. Unlike you, who have repeatedly suggested I was making errors or lacked depth in my comprehension of ballistics without ever citing examples, I have always described anything I objected to and why. All you appear to be capable of is casting vague aspersions and condescension without substance.

Let's not forget to compare and contrast to your most recent posts the gibberish you started out with posting in your (half-dozen) pastes of your RPM Theory:
“the bullet is unbalanced or becomes unbalance due to obturation in the bore during acceleration. The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around it's geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release. After exiting the muzzle, the geometric center will begin to revolve about the center of mass and it will depart at an angle to the bore (line of departure). At 54,000 RPM to 250,000 RPM, depending on velocity and twist, the centrifugal force can be tremendous. It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.”

The above bunk is what I have a problem with, not the work of professional ballisticians -- your improvisation, Larry. I have no problem with the italicized cribbed part, and never have. If you are attributing all of the above to Rinker, then yeah Larry, Rinker is spouting bunkum (truly awful aphysical wording at the very least) and you couldn't tell the difference and quoted it repeatedly. Please do provide a page and paragraph citation, or post a copy -- I really doubt that is a verbatim quote, as no professional ballistician with a rudimentary understanding of physics would write that way (and no editor would allow the typos and redundancies). 'Fess up as to what parts are your own, or post a copy of the original text in full from the book.



Yeah, I like my own professional references, Larry. I'm pretty sure Rinker would be a great big step down from re-deriving analyses from old AGARDOGRAPHs. Maybe your choice of references is the source of the problem, here. On the other hand, I would hate to impugn Rinker when I suspect it's your lack of comprehension that's at fault.

The only thing you made obvious with your initial reply is that while you've stated the bullet is flying in a helical trajectory due to centrifugal force (an impossibility), you have absolutely no idea as to the frequency of the trajectory, it's size, or how you would go about predicting them. Kind of what one would expect with a fictional helix resulting from a nonsense theory, right? :D Your answer even sounds like you are wondering if it's much of a helix at all. Which, as you probably guessed, is exactly what I was going to tell you how to demonstrate for yourself by test -- that there is no helical trajectory causing dispersion for all our high velocity cast bullet flights. The shot dispersion in Bullshop's and my own tests is entirely attributable to other factors. And in fact, the relevant (correct) portion of your theory that you cribbed doesn't result in a helical motion of the bullet post separation from the crown but a simple constant velocity crossrange drift (velocity in the plane normal to the bore axis).

You keep talking about 200 yards, but you are skirting the fact that all of Bullshop and my testing has been at 100 yards or less, and yet you have continually insisted that our results evidence the results of your theory. You can't have it both ways, Larry. Either Bullshop's good results at 100 yards and my constant MOA vs. range call into question your theory, or your theory says nothing about our results.

You cannot have a helical trajectory of a free-flying bullet without aerodynamic forces and bullet yaw, which you have never made any mention of, and occur irrespective of any RPM threshold. Conversely, the simple crossrange drift that results from an offset between the CG and geometric center at separation from the muzzle also occurs regardless of RPM, but has no possibility of resulting in a helical trajectory. While it is true that you can have strength of material related failures as a function of all the stresses imposed upon a bullet, and that these are likely to result in bullet imbalance, these are not exclusively related to RPM, and will be a STRONG function of caliber with rpm related limits decreasing with increasing caliber, the opposite of your predictions. Strength of material related failures can occur because of not only RPM, but too much angular acceleration, skid, "set-back", gas cutting, bore roughness, etc. "Obturation," or the bullet sealing the bore against gases, while solely mentioned in your theory in the context of a displacement between the CG and geometric center, in and of itself has nothing inherent to do with bullet imbalance and RPM. Aerodynamic forces due to rotation about other than the geometric axis of symmetry will cause increasing dispersion with range (as will gravity in combination with muzzle velocity SDs and wind), but has nothing to do with "centrifugal forces" or an RPM threshold (other than as related to bullet damage, which really is a "NO, DUH" isn't it). Lateral dispersion down range due to the misalignment of CG and the geometric center and the event of separation at the crown do not result in the creation of a radial force -- they result in the release of the radial force and the departure of the round from the bore with a tangential component of velocity. Again, any "helical" downrange trajectory of significance has to be due to aerodynamic forces acting on lower frequency nutation of the bullet nose. Larry, you have conflated enough different phenomenon and are just a tiny bit right and a lot wrong in enough different directions at once that I don't see how you think you have any passing understanding of this subject matter, much less judge yourself competent to remark on the qualifications of others. Are you under the impression that our dialogue so far has been of benefit to me, or your ignorant condescension other than an annoyance? It's been pretty clear to me, at least, that you've just been posturing for the benefit of others rather than engaging in any substantive dialogue on the points. You've been rude and condescending to one member after the other on this thread... frankly, I'm not seeing much redeeming virtue in your having a keyboard at all.

The more uncomprehending pronouncements on statistics and ballistics of yours I read, Larry, as contrasted to the obviously cribbed passages (so strongly contrasting to your own ctrl-v'ed theory) the more I become convinced that this whole (three year?) debacle of your RPM theory is entirely a result of your lack of reading comprehension. I think all of this could have been avoided if you simply had stuck to what others had written, distinguished between your own efforts and that of others, and attributed the work of the professionals to the professionals instead of cribbing some and improvising the rest on your own in your CTRL-V'ed "theory". Throw away all the parts of your copied franken-theory that are original but wrong (the helical trajectory absent any consideration of aerodynamic forces, the centrifugal force post bore departure, the obturation (well, not wrong but unnecessary)), and keep the part that is completely unoriginal but right (that a bullet will rotate about the geometric center while in the bore, and that the center of gravity will consequently depart the crown with a tangential velocity) and you will be back to a semblance of reality pertinent to what Bullshop and I tested (and incidentally, without a Larry RPM Theory to paste).

Despite your suggestion and your own contrary example, I don't condescendingly assume that anyone is uneducated, or that fools (even principally) reside among the uneducated. You have caused me to have doubts based on what you've written, however, and you have stated doubts about me. I propose we do a little exercise to test our respective reading comprehension of what you yourself have copied:
Tell us according to the copied (correct) part of your theory what the deviation on target of a 40 grain .224 diameter bullet is fired from a 1/14 twist rifle at 100 yards, as resulting from a .003 offset in the mould halves (resulting in the nose being that much longer and the base flat). Let's provide the answer in Minutes of Angle, and use a nominal density of lead of .4 lbs/inch^3. This scenario should sound relevant to you in the context of the recent tests.

I'm wondering if you'll even be able to start, even though the part of your theory that you copied which is correct is the part that tells you how to do it! I did the calculation from first principles, Larry -- but you go ahead and do it open book. I'll show all of my work, Larry -- please do show all of yours. Maybe one of Rinker's neat ballistic's equations will give you something to "play with."

I'll post the answer here tomorrow. I'll predict you won't even try... but will just offer more of the same condescension and personal attack. Come on Larry, put up or shut up. You want to pretend that you know anything about external ballistics as compared to incorrectly cribbing from a reference? Then demonstrate you know something about the trivial basics like conservation of momentum according to words you've been presenting in your own theory for years. When you get the answer maybe you'll be so thoughtful as to explain what it means, and why it's necessary for us to have a Larry RPM Theory in light of it?

As far as your other points, Larry:
you don't understand basic statistics well enough to argue them yourself (instead you copy what you don't understand, misapply it, and then say -- well, all the experts can't be wrong! Which is exactly the point -- they aren't Larry, you are).
you don't understand that angular acceleration increases with increasing radius and believed exactly the opposite until I corrected you.
you don't understand that a bullets trajectory may be modelled as an equation of a point in space (I thought the helix thing as a choice of trajectory as explained as resulting from RPMs & "centrifugal force" in your theory is absurdly aphysical, but it was your theory, so please don't stick me with that);
or that there is no role of "centrifugal force" in free flight "causing a bullet to fly in an ever expanding helix" (ever heard of principal axes, you know, the ones that by definition pass through the center of gravity?);
easily the most offensive of your many peccadilloes: you insist on making up your own definition of "threshold" when we all have dictionaries.

After all of the above, you are going to try to paint me as the ignorant one here? :D


Larry, I am degreed in aerospace engineering and earned a doctorate, and while I did some work for the university to pay my way, and some NASA centers over the years, I spent most of my time in industry. But no matter where I worked or how I earned a living, I have always had the honesty to concede the limitations of my knowledge when confronted by reality. I would never be caught dead going around and inventing new meanings for perfectly good words like "threshold" to try to obscure the fact that my pet predictions had failed time and again. :violin:

I think there are some pertinent things I said in the prior post that may help some of the other folks here with some of the redundant points you've just tried to make that were previously answered.



Here's one:



I'm sure there are a bunch of folks here who will get the point of the above, Larry, and realize on their own that there isn't a one-size-fits all fixed sample size for every situation, every population, and every statistical inference. How many data points are required to correctly make a relative determination about the size of the means of two different populations depends: 1) on the proximity of the means; 2) the variance of the populations; and 3) the desired statistical confidence. When you start talking about linear or multiple linear regression, the number of model parameters (degrees of freedom) and geometric distribution of the points in the independent variable space also become important. It may be I am talking about something you don't comprehend, Larry, but don't you think that means you might want to listen to what I am explaining to you a little more closely?



By the way, to the gentleman who posted earlier about using standard deviations instead of group size:
I completely agree with his point. If you make the usual random normal distribution assumption, group sizes will statistically grow with increasing sample size ad infinitum... whereas estimates on the standard deviation, x and y, will converge about their true values according to the central limit theorem, and you can estimate the confidence and error of the estimates. They will also show evidence of the effects of muzzle velocity variance and wind dispersion which "group size" will combine (and this is a potentially confounding factor for falsifying your "RPM Theory" Larry as range increases).

The reason folks do it the way they do is that group size is easy to measure with a ruler, whereas calculating the standard deviation on x and y requires locating each hole, calculating means on x and y, and then calculating the respective standard deviations. In my experimental design for the hornet test I ran it with individual targets for each shot for each variant, with the order of the shots distributed to average out fouling and heating effects between the variants. Consequently I had to measure the individual shots and compute SDs, group sizes, etc.

DrB





:shock:

Jerry

[Suo Gan]

Larry has been continually chastised for just basically stating what he has observed and his resulting question and hypothesis. He never claimed to have a PhD in ballistics, nor have such an intimate understanding of the letter of ballistics law as to be THE final reference. Just a layman (who can actually use the scientific method this is not just meant for elite scientists) telling what he saw and why he thought so.

I remember reading threads about this years ago and thinking 'jeez' this guy can sure be humble in the face of so many butt heads. A lot of people start their threads here in a way that is chaffing. They come off as pompous, and even though many of them start with "I mean no disrespect" they end up going ad hominen on him.

The way I see it is Larry is a man who wants to learn and loves to shoot, and is not afraid of bringing it all to the table to be scrutinized by the anointed few who really get cast boolits. .

To me Larry made a valid hypothesis and has a better than the average persons understanding of physics (take my ma for instance)...something he apparently got into because of his love of shooting.

I frankly could give a rip about most of what the anointed few do or think, because I have found they are a clique and hold the info they have like greedy children, and tell the world the way it is in code only a conehead could understand and if you question them they tell you to go and look it up.

I appreciate the way Larry is forthcoming with his knowledge. He is a good man. Cut him some slack. If you know more about physics than he does, do it with the heart of a teacher not the heart of some arrogant professor.

So being a Dr. I assume you have had public arguments with other PhD's then? I thought all PhD's were in lock step at all times. The way learning and understanding happens is EXACTLY what Larry is doing.

There I feel better.

[swheeler]

All I can say is thank goodness noone had to wade through any bovine fecal matter spread about by "Curly Joe Metal" If the "laughing guy" at Sierra Bullets read any of this, I'll bet he is really laughing now!

[44man]

All of this gets crazy. All of my life I have worked loads for accuracy, accuracy is my game. Take any gun and any bullet or boolit and find where it does the very best. Take any twist or caliber and find the sweet spot with what you shoot.
END! :bigsmyl2:
Paper figures suck, I do not believe in muzzle energy or velocity to kill an animal or to shoot smaller groups. Find what your gun shoots best and then make the boolit or bullet work in that range so it kills game.
Find what shoots the best groups----END!
If a boolit shoots perfect at 1500 fps and someone says it will shoot at 3000 fps, HOW?
The base limit can not be extended, ballistic data can be formulated around ONE boolit at one velocity. That is why a sniper can make kills at unreal distances. The base limit is kept the same and the flight path is known. It still comes down to the accuracy, bullet, match to twist and velocity.
Take one boolit at one velocity that shoots good groups and take up the velocity, what do you need? A different twist rate, plain and dirty.
This threshold stuff is funny because the accuracy point has been exceeded far back.
Does anyone realize the same thing happens if you slow the same boolit DOWN looking for a light load with less recoil. You need a different twist rate.
One single bullet will shoot best at one point. If you change loads, does that mean the threshold has been exceeded---SURE. Groups will open and that is fact. Just why push more and more expecting the same bullet to continue to shoot good to some crazy velocity?
Junk science, like Greenhill applied to other then a cannon.
I have to agree with DrB. But not the helical rotation of a bullet because it is there. And not with Larry because it does not increase with distance, it is reduced. Larry exceeds the accuracy limits and names them "thresholds."
Mechanical limits and some common sense will make a gun shoot, not theory.

[leftiye]

I don't think that DrB doesn't say that helicals (spirals) don't occur (all the time)[how's that fer grammar?]. I think he said they don't happen without a wobbly (footballing) bullet planing on air resistance while rotating. Larry says that out of balance by itself (pushed by centrifugal force) causes spiraling that doesn't settle down, but becomes wider and wider (out of control boolit if you ask me). Larry doesn't believe in air resistance from what I could tell. At one time he didn't believe that spiraling boolits went to sleep because of rotation stabilizing them (how can a factor responsible for destroying accuracy stabilize a boolit that is yawing?) either. MacMillan of course was wrong too.

[DrB]

Larry has been continually chastised for just basically stating what he has observed and his resulting question and hypothesis. He never claimed to have a PhD in ballistics, nor have such an intimate understanding of the letter of ballistics law as to be THE final reference. Just a layman (who can actually use the scientific method this is not just meant for elite scientists) telling what he saw and why he thought so.

Larry has done things like explain to me how I didn't know what the word "threshold" meant, why my data was simultaneously irrelevant to his theory, but at the same time explained by his theory, and how I didn't understand anything about ballistics but really should go "read a book for beginners." Those aren't endearing qualities to me, coming from a stranger.



I remember reading threads about this years ago and thinking 'jeez' this guy can sure be humble in the face of so many butt heads. A lot of people start their threads here in a way that is chaffing. They come off as pompous, and even though many of them start with "I mean no disrespect" they end up going ad hominen on him.

My experience with Larry has been different than yours. I've offered Larry an opportunity to engage in a polite dialogue (he started out not doing that IMHO), and demonstrate his mastery of something incredibly basic. I agree that you can argue my reaction to his condescension ad hominem, but my challenge for him to perform something trivial that is explained by the words he's been repeating is pertinent.



The way I see it is Larry is a man who wants to learn and loves to shoot, and is not afraid of bringing it all to the table to be scrutinized by the anointed few who really get cast boolits. .

To me Larry made a valid hypothesis and has a better than the average persons understanding of physics (take my ma for instance)...something he apparently got into because of his love of shooting.

I frankly could give a rip about most of what the anointed few do or think, because I have found they are a clique and hold the info they have like greedy children, and tell the world the way it is in code only a conehead could understand and if you question them they tell you to go and look it up.




I was about to comment on this thread when I read this:


:shock:

Jerry

You both are absolutely correct -- I was just a condescending @ss towards Larry.

My opinion, particularly after three or four cups of coffee, is that the problem with politeness as a universal virtue is the jerks of the world get a free license to be loudmouthed condescending jerks. I do not assume that I know more than the next guy, and as I have said before -- experiments are costly, we all benefit from sharing our results, and we all benefit from the free exchange of ideas.

If Larry wants to answer a point directly and topically instead of saying "I've got a great book for beginners you should go read," then we can have an unpolluted and polite conversation. If it's a book for beginners and he's read and understood it, he could just as easily share what he's learned, and when pointing out a good reference omit the condescension of pointing it out that it's a book for beginners.

If he wants to make the following kinds of cheap shots towards others:


BTW, you're not the only one who went to college. Some of us even managed to graduate

Well, in my book that kind of cheap jerky comment merits a response in kind. The particular member that Larry chose to direct that towards is one of the sharpest, most polite, and resourceful individuals I've seen on this board at getting the right answer to noobs and pertinent questions on a thread that are of benefit to everyone. The above hasn't been the only cheap shot I've encountered with Larry -- a flatly polite and factual response has been the exception. My experience with Larry is limited, but I judge the man on what I've seen.

I would be glad to have a respectful discussion that focused on the subject at hand instead of calling into question the qualifications of the involved parties, appeals to authorities (not understood by the person referencing them) or cheap shots. I said exactly this on the preceeding thread, made my first post here, and immediately got what appears to be Larry's standard tone when encountering anyone who doesn't fall in line with his preconceptions.



I appreciate the way Larry is forthcoming with his knowledge. He is a good man. Cut him some slack. If you know more about physics than he does, do it with the heart of a teacher not the heart of some arrogant professor.

I will freely and sincerely apologize when I learn that I was wrong about Larry and how he treats his fellows.

Larry may be a great man in many respects -- but it is not a great quality for a man to sneer at the bona fides of their fellows instead of speaking to them directly.

The smartest and most talented rocket scientist I ever had the honor of working besides was a highschool graduate and a SEEBEE in WWII. He ended up the most senior design engineer, and was called back from retirement by the company I don't know how many times. I met one of the smartest and most all around knowledgeable men I ever met at the same company -- he was trained in a machinist apprentice program at Sandia, had been a tool & die maker, done red iron construction, worked as a manufacturing engineer, a senior combustion devices design engineer, and a senior combustion devices test engineer.

Degrees don't matter: talent, knowledge, experience, and understanding do. A patience and understanding for one's fellows is a nice quality to have too. [smilie=1:




So being a Dr. I assume you have had public arguments with other PhD's then? I thought all PhD's were in lock step at all times.


ARE YOU KIDDING?!!! :) Yes, of course you are. There are arguments a plenty, but rarely condescending among folks in a field -- because the math and observations are key. You should leave appeals to authority out of it -- if you are having a discussion at that level in your field -- you should be an authority, and if you don't see the next guys error in math, observation, or theory, you explain what you don't understand or go back to the books. If you have something to defend, you do it on the merits.

Saying, "I've got a book for beginners you should read" to someone in their field -- well, that's just not the sort of thing that is done. Sharing one's library and opinions of books is a compliment, saying the former is taken as the slight Larry intended it to be.



The way learning and understanding happens is EXACTLY what Larry is doing.


The sharing of observations and theories -- yes. Larry's squashing and belittling of dissent and honest questions -- No. Simultaneously belittling inconvenient data while suggesting it is both proof of a personal theory and cannot exhibit evidence of the personal theory. -- No.

If you would, please go back to prior posts of mine. You'll find I've never belittled Larry's observations or range reports. While I disagreed with his theory as worded, my first (and second, and third, and fourth, and fifth) response was polite, and to do Larry the favor of including two different ranges of test points in my own test so as to quantify any MOA increase as a function of range. I even sliced the data for him in a pertinent way to share what I found... the response wasn't "gee, thanks, that's interesting. Hey, if you get a chance, maybe you could also do this other thing? Here's my concern." It was quite the opposite in tone.



There I feel better.


Me too. :)

Best regards,
DrB

[Junior1942]

>I agree that you can argue my reaction to his condescension ad hominem, but ....

I think you mean "ad infinitum" which is where this topic is going.

[9.3X62AL]

This subject surely attracts a LOT of attention and commentary. I'm way outta my depth here, and have no business criticizing Larry's or Dr. B's assertions. Their texts provide DEFINITE food for thought, though--and now that I'm starting to push boolits out of my "comfort zone" in the 9.3 x 62 (1700-1800 FPS) things may get "interesting".

My plan is to push the wonderfully accurate 270 grain tangent ogive flatpoint into the 2000 FPS+ area code, if they will stay there and remain accurate. Once the upper level velocity limit is reached with homogenous-alloy (92/6/2) castings, then softpoints cast with 100 grain pure lead donor slugs will be tested to verify if the two-alloy hunting boolit maintains accuracy at that speed--or whether slumping occurs under accelleration and accuracy degrades. I will dial back the velocity to a level that maintains accuracy, in that instance. So far, at 1700 FPS there has been no significant accuracy variation between the softpoints and the single-alloy castings. THAT is encouraging. IMR 4320 is the first fuel "on deck" for the velocity trials, stair-stepped in 20-round increments for ten-round groups.

ETA--If my calcs are correct, at 2000 FPS this boolit should be running ~110,400 RPM, and at 2,200 FPS the RPM should be ~121,440. The twist rate is 3 turns per meter, about 1 turn in 13.1".

[Nrut]

Al,
Pure Pb can be pushed to 2000+ fps patched and the nose is not patched so I think your goal is not unreasonable.
Food for thought anyway..
I haven't worked with my X62 for several years but found H4895 to shoot the best with a 260gr RCBS .377 bullet sized down to .369"..


DrB,
Your problem is that you are a unrepentanted RPM Threshold Heathen! :drinks:

IMO you and Bull Shop should just continue to post your work with high vel. in the hornet and ignore Larry and this thread completely ..
You don't have to prove to Larry that the 144,000 RPM threshold is bogus and you can't anyway because "his" threshold is movable or can be pushed..

PM sent on the rest of the story.. [smilie=l: :Fire::Fire:

[9.3X62AL]

I hope everything "holds together" past 2000 FPS. Range time has been problematic this summer due to interferences from non-hobby factors like medical crud. Medical stuff means a 250 mile round trip, and I spent 3 of last week's 5 days doing that stuff. 2 more days next week, and at least one day the following week. PITA!

[DrB]

I don't think that DrB doesn't say that helicals (spirals) don't occur (all the time). I think he said they don't happen without a wobbly (footballing) bullet planing on air resistance while rotating. Larry says that out of balance by itself (pushed by centrifugal force) causes spiraling that doesn't settle down, but becomes wider and wider (out of control boolit if you ask me).

Yes. Helical trajectories from aerodynamics acting on a bullet precessing like a top (nutation) absolutely does occur, but has nothing to do with "centrifugal force."

Nutation isn't the problem with each and every gun group over some particular RPM, though. Most things that happen differently from shot to shot can contribute to inaccuracy... cast bullets can be easier to damage than jacketed (and this can happen through a host of mechanisms), and that can result in several problems. Leading affecting successive shot's velocities (different muzzle pointing due to vibrations), uneven gas venting at crown departure shoving the bullet, tangential velocity at departure from the bullet due to CG misaligned with the geometric center, aerodynamic forces in flight due to geometry imperfections (most of the lateral components are averaged out because of the high spin rate relative to target distance), and nutation + aerodynamic forces (which can impact accuracy because the spin rate is low compared to target distance).

Accuracy is one measure of a gun -- I think most of us catch different bugs at different times -- small caliber, large caliber, high velocity, accuracy. I agree that an interesting gun is an accurate gun. High velocities can be nice too, if accuracy is acceptable. If you can't hit what you are aiming at, might as well be lighting off a firecracker.

I believe I may be able to get my gun to shoot as well with cast as jacketed at comparable velocities (~3200fps). There is still more to try, and I've had some great tips by some of the forum members who do get good results at higher velocities. Bullshop and other's have done some impressive things. As I said on my original thread, I was astounded that Bullshop's results were as easy to replicate without lead fouling as they were.

I'll be posting some calculations regarding the impact of measured bullet imperfections on my prior test shortly... if I've got it right, as I believe I have, it appears as though I couldn't have expected to shoot a whole lot better than I did with the unsorted and imperfect bullets that I had, which is encouraging. Prior best accuracy + explained bullet problems is pretty close to group size, so that's encouraging if improved bullets provide what I think they will. Also, it's testable so if it turns out to not be as important as I think I should be able to show it.

Best regards,
DrB

[Nrut]

I hope everything "holds together" past 2000 FPS. Range time has been problematic this summer due to interferences from non-hobby factors like medical crud. Medical stuff means a 250 mile round trip, and I spent 3 of last week's 5 days doing that stuff. 2 more days next week, and at least one day the following week. PITA!
I hear you Al on the medical crud!
Wish you well on that and achieving your 9.3 goals..

[Junior1942]

>I believe I may be able to get my gun to shoot as well with cast as jacketed at comparable velocities (~3200fps). There is still more to try, and I've had some great tips by some of the forum members who do get good results at higher velocities.

A 1 - 20 twist might get you there--around 115,000 RPMs. "Might," I said. "Won't," I believe. Keep us posted.

[9.3X62AL]

I hear you Al on the medical crud!
Wish you well on that and achieving your 9.3 goals..

Thanks kindly, sir. One of the 4895s will be next in line if the slower IMR-4320 doesn't work out. WW-760 might get a test-drive, too.

[DrB]

>
A 1 - 20 twist might get you there--around 115,000 RPMs. "Might," I said. "Won't," I believe. Keep us posted.

Wilco, Junior. Reality is. If it won't, it won't...

Bullshop's already got a four shot at 100 that's touching with one wide flyer (opens it to about 1" for 5) and one really wide flyer (opens it to about 2" for 6) at ~196,000, rpm. That and my initial back of the envelope look at the effect of CG shift makes me optimistic.

We'll see.

[DrB]

I believe this is from Understanding Firearm Ballistics, by Robert A. Rinker, via LG. Similar quotes may be found in other references:


The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around it's geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release.

OK, so Rinker et al are discussing this as though bullet/crown separation is a 2D problem (it's not, and that concerns me some). This, however, is really easy to run the numbers on, and should be very easy to test to see if range results are as expected (more on that at bottom).

When you spin the CG of a mass about a radius and then release the force that has been accelerating it towards the center of rotation, conservation of momentum dictates that the bullet departs in the direction its center of mass was going at the moment of release. This tangential component of bullet velocity (in the crossrange plane) just depends on muzzle velocity, twist length, and the offset of the CG from the axis of constrained rotation (geometric center) in the bore. Please note that when I say "crossrange" here, I am not just talking about left vs. right, but a plane normal to the downrange direction that includes up-down-left-right directions.

So, if we calculate the distance between the CG and axis of rotation we've got most of our answer.

To give a concrete example/context to this, what I found when I measured some bullets picked from a sample of NOE225107 castings from a particular mould was that the nose halves were about .002-.003 different in length, with one half of the bullet on one side of the parting line apparently being that much longer than the other. A fingernail would catch going one way across the parting line and not the other. The sprue plate produced what looked like a perfectly flat base, and I didn't notice any issue with the radius from one half to the other on the base edge or other abnormality. Concentricity seemed to be decent to under half a thousandth. My conclusion from the above was that the mould halves were about .002 to .003 out of alignment along the axis of the bullet, resulting in one half of the bullet being .002 to .003 thousandth longer than the other.

Let's define some variables we'll need:


dr == distance bullet cg is off the normal from the geometric axis (inches)
TL == Twist Length (inches per revolution)
c == caliber (inches)
v == down range component of velocity (feet per second)
vldr == lateral component of velocity due to dr (inches per second)
wrot == bullet rotation rate (rev/second)
R == Range defined as 100 yards
dMOA == deflection at target in Minutes of Angle from nominal path (one-side deflection, maximum group size increase will be twice this)
NO == Nose Offset (inches)
Wb == Weight Bullet (pounds)
Wdef == Weight bullet defect (pounds)
rdef == radius to center of mass of bullet defect (inches)
Pi == the ratio of the circumference of a circle to the diameter
rhob == density of bullet lead (pounds per cubic inch, ~.4 lbs/inch^3

The CG offset resulting from this is really easy to calculate. I'll treat the rest of the body as axisymmetric (meaning the CG absent the nose offset is coincident with the geometric center).

The mass of the nose offset is given by density times volume:
Wdef = rhob * (NO*c^2*Pi/4/2) = rhob * (NO*c^2*Pi/8)
(dimensional check: lb/inch^3*inch*inch^2= pounds -- yes, pounds are force, not mass, but it ends up working out here because they just end up in a ratio with other pounds)

The radius to the cg of the nose offset defect is given by:
rdef = 4*c/(6*Pi) = c*2/(3*Pi)

The radius of the CG is given by:
dr = 0*(Wb-Wdef)+Wdef*rdef/Wb = rhob*(NO*c^2*Pi/8)*c*2/(3*Pi)/Wb = rhob*NO*c^3/(Wb*12)
(dimensional check: pounds/inch^3/pounds*inch*inch^3=inches)

Now, the bullet rotation rate will be:
wrot = 12*v/TL
(dimensional check works out to 12 inch/ft * ft/sec/(inch/rev) = rev/sec)

And the tangential velocity will be:
vldr = 12*v/TL*dr*2*Pi = 24*Pi*v*dr/TL (inches per second)

The flight time to target will be about:
100 yards * 3 ft / yard/v = 300/v (seconds)

Thus:
dMOA = flight time * vldr *(inch to MOA conversion)= 300/v*24*Pi*v*dr/TL /1.0472 = 7200*Pi dr/TL
(dimensional check: seconds*(inch/second)/(1.0472 inches/MOA@100yd) = MOA

substituting dr:
dMOA = 7200 * Pi/TL * rhob*NO*c^3/(Wb*12) = 573 * Pi * rhob*NO*c^3/(TL *Wb)

(Now, I am neglecting above the impact of drag on lateral velocity/induced angle-of-attack lift that retard the lateral component of velocity as well as any turning of the bullet into the lateral velocity, and the decay of downrange velocity. This should be fine for an approximation at close range, but not so much the further we go out. How the MOA effect will be impacted depends on the relative rate of retardation of the lateral component of velocity and the "turning into the wind" of the projectile in relation to the downrange component of velocity.)

So, dMOA = 573 * Pi * rhob*NO*c^3/(TL*Wb)

First of all, if anyone has the inclination please do check my math. I don't like doing this in free text as it's a lot harder to spot errors in arithmetic this way... I checked units as I went, but anyone who finds something that looks like an error, please let me know.

Now, for our particular example, this yields:
dMOA = 573 * Pi * .4*.003*.224^3/(14*(40/7000)) = .303

So the maximum group increase in size from this alone is .61 … Note that whether this is an underestimate or overestimate depends on the relative rate of decay of the downrange and crossrange velocity components.


Also, it's kind of interesting to note the mass of this defect (in grains):
Wdef = rhob * (NO*c^2*Pi/8)*7000 = .166 grains

and the radius shift of the CG is just .0002...

Now in actuality we will have other defects in the bullet. We were fortunate here, because we had a defect of roughly known geometry that we could approximate the impact of. But .166 grains doesn't seem like very much of a defect size to me, and the defects centroid was only at .048” from the center (43% of what it could have been if a bearing area defect)! It may be interesting to bound the maximum possible impact of a weight defect size on group size due to this mechanism. More on this later.

So, if the above are right, it isn't unreasonable that one might see:

group sizes open up significantly as a result of bullet weight variation displacing the CG of the bullet from the mass center -- this should be observable at any range with magnitude of the impact to MOA depending on the relative rate of decay of lateral vs. forward velocity-- (yeah, I know a bunch of you are saying "no duh" :) but it's interesting to me to see what the numbers are relatively.)
non-axisymmetric defects induced on the surface of a bullet have a much greater effect than those close to the center of the bullet (effect proportional to radius from centerline to defect)
group sizes (as measured in units of angle) due to lateral velocities induced at the muzzle will either open up or close up with increasing range depending on the relative rate of decay of downrange vs. crossrange velocity components.
At close range, the equation for change in group size in MOA due to (pre-existing) imbalance is going to be independent of muzzle velocity, and dependent solely on twist rate and the degree to which the defects displace the CG from the geometric center.


First thoughts on how to check this at the range:

take a sample of my bullets with nose half offset
determine by fingernail test which nose half is which
mark each nose with sharpie
seat the bullets
Mark the cartridge head with the clocking of the bullet
Fire a group comprised of a large number of bullets with half oriented one way in the rifles chamber, and half oriented 180 degrees (this would best be done at close range, say 25 yards off a bench, to minimize the effects of wind and gravity+MV variation)
Fire a group comprised of a large number of bullets with all bullets oriented the same way
the difference in group size should be less than but close to twice the expected deflection of the bullets (.6")


If everything is as it should be, and assuming the nominal group shape is pretty round, you would expect the half-and-half 180 degree opposed group to show a somewhat elliptic shape, and greater size than the other target with all bullets oriented the same way. The more accurate the rifle/load combination is to start with, the easier it should be to distinguish between the two groups. (You know, I remember reading at least one member here who said he clocked his bullet orientation from the mould for a rifle and chambered each with the same clocking and it made a big difference for him. Don't remember who I read did this, but if it makes a difference with a wonky mould I'm sure others must have already tried this. It would be interesting to know who's done it, why, and what they found.).

OK, so I think the above approach to testing is doable but a bit problematic because I have relatively few of the original run of bullets left. It is likely to reduce the number of shots required to distinguish between the two populations reliably by using standard deviations instead of group size. I haven't thought that through, entirely, though.

Another test may be to just do as has been suggested to me already by another member here and carefully weight sort my bullets for a test using only the very heaviest bullets. While low weight bullets alone aren't theoretically required to be out of balance, it makes sense to me that if they are low weight due to surface fill out failure (potentially particularly bad per amount of defect weight) or because of internal voids/inclusions, then the magnitude of the overall problem may increase with lower weights.

A more controlled approach would be to drill out a cavity of known depth and volume in the lube grooves of a bunch of bullets, repeat the calculation for that, and run the experiment as above.

Best regards,
DrB

[44man]

I don't think that DrB doesn't say that helicals (spirals) don't occur (all the time)[how's that fer grammar?]. I think he said they don't happen without a wobbly (footballing) bullet planing on air resistance while rotating. Larry says that out of balance by itself (pushed by centrifugal force) causes spiraling that doesn't settle down, but becomes wider and wider (out of control boolit if you ask me). Larry doesn't believe in air resistance from what I could tell. At one time he didn't believe that spiraling boolits went to sleep because of rotation stabilizing them (how can a factor responsible for destroying accuracy stabilize a boolit that is yawing?) either. MacMillan of course was wrong too.
The Helix, I called it a corkscrew, around the flight path never showed a wobble of the bullet itself (Jacketed by the way.) I watched thousands of them and could never pick up any other then the bullet staying in line like a well rotating football. Holes in targets were dead round. The bullet was over spun and did the tricks. As distance increased, it would settle to the flight line. Went to "sleep."
Just a slight increase in bullet weight and length stopped it dead.
This is different from a wobbly boolit that can keyhole.
What is Larry talking about? Is it the corkscrew around the flight path or is it a boolit that wobbles with the nose rotating more then the base or the base wobbling more then the nose? That is Yaw and must not happen for accuracy. That has nothing to do with an RPM threshold.

[Pat I.]

Am I the only one who has absolutely no idea what's being said in some of these posts!! Shooting sure seemed a lot easier back in the days before internet forums.

[44man]

Am I the only one who has absolutely no idea what's being said in some of these posts!! Shooting sure seemed a lot easier back in the days before internet forums.
I agree with you. We made guns shoot. Guns shoot at one point for each bullet. If the bullet will not shoot, it is wrong for the gun.

[9.3X62AL]

Pat--

I'm enjoying the flow of information, though I do have to back up and do a little definition search from time to time. Some of what is being explained technically above is info that shooters sensed intuitively by virtue of range/field experience, which doesn't always translate to clear text.

[leftiye]

44man, I suspect a slight wobble (B calls it precession) which cannot be seen is causing the spiral that you do see. It seems there would have to be some wobble (please don't take issue with my terminology - you can call it what you want. I know that "wobble" isn't a scientific term). Not at all to be arguing with you. The insight that it is overspinning causing the phenomenon is valuable. I suspect that there are probly a variety of reasons for precession.

As for what Larry is thinking - as nicely as I can say it - whatever it is it doesn't happen. I've asked Larry these questions before (for three years) and got no answers. According to DrB who is the best source we've seen here to this point, rpm and centrifugal force do not cause spirals. My own insight has been (and again, Larry has been presented, and did not explain how his hypothesis got from assertion to produced phenomenon - or causality) that a boolit with a center of balance that was offset from and parallel to the center of form would make sucessive lurches in one direction ad infinitum (no spiral) until the boolit impacted something (definitely not the target point). Multiple boolits would seem to want to create a shot gun like pattern as each defective boolit would vary, direction of lurch and amount of deflection would vary, and point of impact would not be predictable.

[DrB]

The Helix, I called it a corkscrew, around the flight path never showed a wobble of the bullet itself (Jacketed by the way.) I watched thousands of them and could never pick up any other then the bullet staying in line like a well rotating football. Holes in targets were dead round. The bullet was over spun and did the tricks. As distance increased, it would settle to the flight line. Went to "sleep."
Just a slight increase in bullet weight and length stopped it dead.
This is different from a wobbly boolit that can keyhole.
What is Larry talking about? Is it the corkscrew around the flight path or is it a boolit that wobbles with the nose rotating more then the base or the base wobbling more then the nose? That is Yaw and must not happen for accuracy. That has nothing to do with an RPM threshold.

I just don't know. I haven't ever thought I was seeing what you describe, but that probably means I haven't done what you have. A friend with a lot of long range shooting experience mentioned to me he thought "corkscrew" was an illusion and not actual bullet motion. If it was my eyeball I might be concerned I was seeing the vapor trail downrange and its distortion due to convection and or some rotation knotting it up.... but that's total speculation on my part.

All I'll say is the cg cannot travel in a corkscrew without aerodynamic forces, and that implies a precessing yaw.

Re bullet yaw, you may try using a "witness plate" to check if your holes had torn edges instead of cut paper as with a wadcutter. I have found before that slight yaw with a spitzer can be hard to distinguish on paper (I was playing with launching ss109s out of a hornet, some reversed, as I was curious if the steel tail ogive would improve static stability enough to make a difference). Witness plate: when high speed photography is too expensive or impractical as with some shrapnel characterizations sometimes folks will use metal plates in a test arena to record impacts. Foil might be a good thing to try. The idea would be to find a material that would most sharply reproduce the silhouette of the penetrating round without having sufficient mass or strength to tip it.

Depending on the frequency successive spaced foils could let you measure a sufficiently large spiral, or nutation. The challenges to this are that the spatial frequency might be too low for this to be practical and successive foils impact could contribute to upset.

Best regards,
DrB

[Cap'n Morgan]

I just don't know. I haven't ever thought I was seeing what you describe, but that probably means I haven't done what you have. A friend with a lot of long range shooting experience mentioned to me he thought "corkscrew" was an illusion and not actual bullet motion. If it was my eyeball I might be concerned I was seeing the vapor trail downrange and its distortion due to convection and or some rotation knotting it up.... but that's total speculation on my part.

He, I was going to suggest an experiment, but a quick Google search revealed F.W. Mann already did that experiment more than a hundred years ago:

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Newsgroups: rec.guns
Subject: Re: [RIFLE] [RELOADING] Load development
Date: 4 Dec 1993 21:32:08 -0500

: What do you mean by 'spiraling'? If you're saying that it's doing the
: equivalent of a barrel roll done by aircraft, I can't see the physics
: allowing that motion of the bullet.

Neither could someone else about ninety-some years ago. So he made some
very interesting tests.

Read Dr. F.W. Mann's Book, `The Bullet's Flight from Powder to Target.' It
has excellent examples of this. Thin paper sheets placed every few feet
between muzzle and 100 yards show the exact spiral path of the bullet.
It even shows how the angle of the bullet relative to its down-range path
is determined. Great reading. Even though it was first printed in 1907.
Physics hasn't changed much since then.

One of these days I'm going to get me a copy of that book!

[DrB]

I agree with you. We made guns shoot. Guns shoot at one point for each bullet. If the bullet will not shoot, it is wrong for the gun.

Guys, I agree with what you are saying... You can do most everything empirically by trial and error. One test is often worth more than thousands of words. The best numerical models run today are still checked against real results, and it's for a reason.

When we try to make sense of things and extrapolate them further into general principles is where things are so easy to mess up. That's why we invented the languages/philosophies of math and science...

I'd rather be at the range shooting than talking about it any day, on the other hand.

I've gotten a number of outstanding PMs from folks who have been shooting high velocity cast with data, tips and tricks. Can't thank everyone on the forum enough for sharing their observations (and that goes for LG, I don't like the way he talks to folks sometimes but I like his range reports).

I'll see ya'll around the other threads. I'll let you know how my own efforts work out.

Best regards,
DrB

[DrB]

:D Wow, this Mann guy must be really really smart to have thought of using witness plates! :)

Sounds like maybe he also used the bullet silhouette at different angles to get yaw?

Alright, cap'n that was a great post, I've got to get his book if it's got that kind of test.

Out here.


He, I was going to suggest an experiment, but a quick Google search revealed F.W. Mann already did that experiment more than a hundred years ago:

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Newsgroups: rec.guns
Subject: Re: [RIFLE] [RELOADING] Load development
Date: 4 Dec 1993 21:32:08 -0500

: What do you mean by 'spiraling'? If you're saying that it's doing the
: equivalent of a barrel roll done by aircraft, I can't see the physics
: allowing that motion of the bullet.

Neither could someone else about ninety-some years ago. So he made some
very interesting tests.

Read Dr. F.W. Mann's Book, `The Bullet's Flight from Powder to Target.' It
has excellent examples of this. Thin paper sheets placed every few feet
between muzzle and 100 yards show the exact spiral path of the bullet.
It even shows how the angle of the bullet relative to its down-range path
is determined. Great reading. Even though it was first printed in 1907.
Physics hasn't changed much since then.

One of these days I'm going to get me a copy of that book!

[357shooter]

Just look here: http://castpics.net/subsite2/ClassicWorks/The_bullet_s_flight_from_powder_to_targe.pdf

[Nrut]

The helix, corkscrew or what ever you want to call it must be some sort of optical illusion, because I use to see the same thing 44man is/was seeing when spotting at handgun silhouette matches back when I did that sort of thing..
It was plain as day on our range as we had the sun to our backs..
Esp. on the rams at 200 m.
Always wondered why I didn't have to adjust for windage for the closer targets..

[Iron Mike Golf]

I have seen with my eyes precession. I was using a spotting scope look dircetly down the gun-target line (I don't recall the magnification). This was in my Army days. Shooter was firing 7.62x51 using an M21 (sniper-ized M14). Late afternoon sun behind us. I could clearly see the precession. I would say I was picking up the round at 75-100 m downrange (I was younger then an my aquisition skills were not developed, yet).

The brightness of the sun's reflection off the projectile varied and I could see the "wobble" after observing a half dozen rounds.

Mk I eyeball (no camera), at that magnification, I did not discern a helix. I'd love to repeat that, using a high speed HD camera hooked up to the spotting scope. Seems like an inexpensive way to confirm or deny this issue regarding helixes and such.

[44man]

The helix, corkscrew or what ever you want to call it must be some sort of optical illusion, because I use to see the same thing 44man is/was seeing when spotting at handgun silhouette matches back when I did that sort of thing..
It was plain as day on our range as we had the sun to our backs..
Esp. on the rams at 200 m.
Always wondered why I didn't have to adjust for windage for the closer targets..
I never seen it when a Ruger was shot. Only the model 29 with 240 gr bullets. Like I explained, it would go away with a 250 gr bullet. So it had to have something to do with twist rate. I don't know what the rate was on the 29. The accuracy was superb with the 240 and it was common to shoot 1/2" groups at 50 meters, open sights from Creedmore.
The reason the S&W never did good at IHMSA was the grip sensitivity. Lay the gun down between relays and I could not hit the same POI. This is a problem with a Bisley too. It is strange to see a 10" change in POI at 50 meters just from the way the gun was held. I proved it on paper over and over, the 1/2" group for 5 shots would move when I picked the gun back up.
One day while plinking we shot at a knob on a dead tree at about 300 yards. The sun was right and bullets looked like tracers. We shot a ton of bullets just watching them for fun. It was easy to walk hits into the knob.

[felix]

Back in the 70's, the standard twist for 44 pistols was 20 for both Ruger and Smith. ... felix

[44man]

Back in the 70's, the standard twist for 44 pistols was 20 for both Ruger and Smith. ... felix
Then I have no answer. I seen it and can not explain it. It caused no problems with accuracy.

[44man]

Back in the 70's, the standard twist for 44 pistols was 20 for both Ruger and Smith. ... felix
I just found some info on the 29's. They had a 1 in 18-3/4" twist.

[9.3X62AL]

I think 44 Man has the S&W twist rate correct--it is used in many of their revolver calibers. Colts used 1-16" most often. 1-20" is Ruger's usual revo twist.

Target 9mm barrels REALLY slow the twist rate down. Barrels optimized for the 125 grainers use a 1-32" twist, barrels for the 147 subsonics use 1-26".

[cbrick]

1-20" is Ruger's usual revo twist.


Pretty much only in 30 Carbine, 44 Spec & mag. Most other single action Ruger's twist at 1-16. In the Super Redhawk double action the twist is also 1-20 in 44, the 454 is 1-24.

http://www.ruger.com/index.html

Rick

[Larry Gibson]

Larry, "lighten up" meant relax, take a breath, and quit being so deadly serious. Insulting and belittling doesn't make for good debating, regardless of facts and data.

Gear

Gear

I am not "deadly serious", I am just serious about the facts and data and what they tell us. I have not insulted nor belittled anyone here. I do not need to "lighten up" just so everyone can agree if that agreement does not agree with the facts and data.

Larry Gibson

[Larry Gibson]

Obturation would be needed to maintain seal and avoid skipping in a HV load with a tight twist. Slower twist and slow burning powder equals not deforming boolit due to further obturation and avoiding skip (and breaking seal) in the first instance by utilizing a slow twist. This arrangement also reduces the forces necessary to increase rotation during acceleration due to lesser angles of attack and due to not producing the rpm in the first place. Rpm in this case is immaterial, it is the result, not the cause.

This is a good example of the interior aspect of the "rpm" theory. Where does it say this is not the operant issue in producing velocity with accuracy?

That is exactly why the arguement of"the 3 barrels Larry used are different" is a dog that doesn't hunt. Even if made by the same manufacture thhe 3 barrels would be different because the twist is different. It is a moot point anyway simply because the affects of the RPM threshold occure during the external ballistic phase, not the internal ballistic phase. The point is the bullet does get imbalanced more in a faster twist than the slower twist during the internal ballistic phase. The increased RPM of the faster twist then casues the inaccuracy if the velocity/RPM is beyond the RPM threshold for that load/componants.

Thank you for answering the 3 barrels are different argument.

Could you give a thread where you got "Remember, you started at 115,200 rpms and 1600 fps." from? I believe I have always said the RPM threshold for a regular cast bullet with a medium burning powder was generally in the 120 - 140,000 RPM range. I also said it could be lowered with a faster burning powder and raised with a better designed bullet and a slower burning powder.

Larry Gibson

[felix]

Smiths: 41 mag has the 18+ twist. The 44 has the 20 twist, Jim & Al. Positive. This was back with the dash 2s, anyway. I am assuming, Jim, you are using higher dash guns in the Smith line. ... felix

[Larry Gibson]

DrB

Wow, “bunkum” from the entire rest of the ballistician world is it/ That is pretty bodacious…….I suppose the world is really flat too?

You may think 3”+ at 100 yards is good but I do not nor do many if we are considering accuracy as the criteria for a varmint cartridge. Apparently you are ignoring the flyers. It is those flyers, as I’ve already told you numerous times, that those flyers are the “evidence” of the bullets possibly exceeding the RPM threshold. Apparently you are ignoring my answers to your questions also. Simply because the flyers do not coincided with the “good” shots they should not be ignored. Simply because my answers do not agree with your analysis they should not be ignored as answers either.

Your discussion of internal and external ballistics is so far off and contrary to any knowledge of ballistics that I will not further waste time with a point by point correction. You really do need to actually study the field of ballistics before making such contrary statements to known and proven ballistic facts. I’m not trying to “paint you as ignorant”. Ignorance can be corrected with education. You continually tell me I am wrong and misapply ballistic facts. However, everything I mention and quote ARE ballistic facts and they do apply. The helical spiral Is a proven ballistic fact yet you call it “absurd”. Again, I suggest you study ballistics before making such “absurd” statements.

Again, a 5 shot sample (either of group size or number of shots in a test of velocity and/or pressure) is not a statistically valid sample. This is accepted throughout the world by all ballisticians, by SAAMI and by CIP. Yet you disagree and say it is wrong, once again I am amazed. As I told the previous poster; the use of ‘mean radii is the mor accurate method of group measurement. However it is more difficult to do correctly and is more time consuming that ctc group measurement. The use of ctc group measurement is the common method understood by most everyone in the shooting world. But, as you mention, to understand ctc group measurement and apply it’s meaning correctly one must understand random dispersion, cone of fire and have a sufficient sample size of group. A 5 shot group sample is still not sufficient regardless of you objections, acceptance of its use and calculations of SDs. If the sample size is not sufficient the SD will also be insufficient.

Larry Gibson

[Larry Gibson]

BINGO. Exactly right, except I don't think he has predictability either.... which really means, without predictability or causality Larry has nothing.

Besides which, Larry's RPM Theory says nothing about why the RPMs he cites... again, he has never posted anything to suggest he has done the least bit of theoretical physical analysis to identify limits. In contrast, the one time he's tried to say anything to me about the way it should trend theoretically as a function of caliber he got the physics absolutely backwards. The correct part of the text he just cribbed, shoot, you can even find the fluffy correct part of it on page 18 of volume 1 of a Hornady Reloading Handbook (or any high school physics text, for that matter).

Drb

You are absolutely correct; I do not and have not done any "theoretical physical analysis to identify limits". I actually shoot cast bullets at velocities below the RPM threshold to above the PM threshold by quite a bit. I measure velocities, pressures and groups sizes with sufficient sample size for confidence. "Theory" has nothing to do with it, I deal with facts and data gained from actual tests. BTW; How many times have I told you about "limits" regarding the RPM threshold?

You certainly have a problem with the rest of the ballistics world. Simply quoting a fact from reliable sources that disagree with your notions/theories really disturbs you. Again, perhaps you should actually study ballistics. The part I quoted from Page 18 of the current Hornady manual has been in all of Hornady's manuals for some years. If you can't find it perhaps someone (since you don't believe or pay attention to anything I say) could explain and "Index" to you?

Larry Gibson

[Larry Gibson]

I don't think that DrB doesn't say that helicals (spirals) don't occur (all the time)[how's that fer grammar?]. I think he said they don't happen without a wobbly (footballing) bullet planing on air resistance while rotating. Larry says that out of balance by itself (pushed by centrifugal force) causes spiraling that doesn't settle down, but becomes wider and wider (out of control boolit if you ask me). Larry doesn't believe in air resistance from what I could tell. At one time he didn't believe that spiraling boolits went to sleep because of rotation stabilizing them (how can a factor responsible for destroying accuracy stabilize a boolit that is yawing?) either. MacMillan of course was wrong too.

Of course i believe in air resistance and wind drift. I actually measure the BCs of bullets (that's a measurement of "air resistance"). However, air resistance and/or wind drift (when the wind is 1-2 mph out of 5 o'clock) do not accout for the non linear dispersion of groups between 100 and 200 yards regardless of DrBs assertion based on his limited sample size at 50 and 100 yards.

Larry Gibson

[felix]

Need about 30 shots, Larry, for the math to be significant enough to be sure of FUTURE results. Current results are assured 100 percent by WHAT YOU SEE IS WHAT YOU GET. If shooting for current results, 5 shot groups are fine. ... felix

[Larry Gibson]

9.3X62AL

ETA--If my calcs are correct, at 2000 FPS this boolit should be running ~110,400 RPM, and at 2,200 FPS the RPM should be ~121,440. The twist rate is 3 turns per meter, about 1 turn in 13.1".

assuming a correct "fit" of that bullet to the throat you should fine very good accuracy at thtat velocity/RPM with the correct powder. I shoot 200 gr cast out of my 14" twist .35 at 2200 fps with excellent accuracy and a 270 gr cast out of my .375 with 12" tist at 2300 fps with excellent accuracy. Both are below the RPM threshold.

Larry Gibson

[Larry Gibson]

44man

......What is Larry talking about? Is it the corkscrew around the flight path or is it a boolit that wobbles with the nose rotating more then the base or the base wobbling more then the nose? That is Yaw and must not happen for accuracy. That has nothing to do with an RPM threshold.

You can indeed call it a "cork screw". In the action where the bullet bullet has this corkscrew caused by yaw and predecssion the corkscrew goes to sleep with in a couple hundred yards. How many exact (I'm sure DrB wants to know or "predict") corkscrews around the flight path until the bullet goes to sleep? It depends; might be one, might be several and it might not even be a complete one. Now with an action caused by too much centrifugal force id different and the bullet may make a compled "corkscrew" during the bullets flight, it may not and it may even take off at a complete tangent. Just as Rinker says and as all other ballisticians say. It is 2 different actions; with the one the bullet goes to sleep and the 'corkscrewing" stops. With the other the corkscrew gets larger (the non linear group expansion) as the range increases or the bullet departs on a complete tangent to the line of flight.

BTW; as mentioned the handguns do not have fast enough twists nor do they have a fast enough velocity to exceed the RPM threshold and have a helical twist as caused by too much centrifugal force. The much smaller helical twist caused by yaw and precession is a different action. Again, the "corcscrew from that action may not make a complete turn around the line of flight and thus will be difficult to "see" befor the bullet goes to sleep (within a couple hundred yards).

Larry Gibson

[felix]

However, air resistance and/or wind drift (when the wind is 1-2 mph out of 5 o'clock) do not accout for the non linear dispersion of groups between 100 and 200 yards regardless of DrBs assertion based on his limited sample size at 50 and 100 yards. Larry Gibson

That would be correct for the most part. However, sighting errors will account for 90 percent of error which would be based upon the mis-reading of the humidity boil distortion. More scope power will allow one to see the amount of boil, but it takes a true weather man to make sufficient offset at the target distance. ... felix

[DrB]

DELETED

nevermind, larry. Kind of pointless writing to someone who can't or won't comprehend and acknowledge simply stated points, instead of making up their own strawmen to argue with. I do find it incredible though that you have managed to repeat the same words for so many years without understanding (or apparently being curious about) what they actually mean.

[Larry Gibson]

DrB

Well, as I've mentioned in numerous threads, the range I use is not a "home" range. I had thought of that test some time back regarding the "bullets go to sleep" discusion. However, setting up targets on frames other than those made for the range is prohibited, which means I couldn't line up the 100 target with the 200 yard target. Also the problem is exasperated because the helical spiral caused by the centrifugal force when a cast bullet goes past the RPM threshold may not even be a complete revolution around the line of flight in entire maximum flight of the bullet. You have your range limitations and I have mine.

Somewhere you seem to want to think the helical spiral caused from centrifugal force makes several rotaions, if not more, in 100 or 200 yards. It does not as I've explained numerous times to you. And no, there is no "predictability of that other than the higher the centrifugal force is and the more unbalanced the bullet is the larger the spiral will be. I have also provided data from a specific test and others that demonstrate the non linear expansion when cast bullets and jacketed bullets are adversely affected by the cnetrifugal force. You apparently have disgarded that data. I also have given you a simple test to conduct with your own rifle that you disregard.

Additionally you seem to be still under the mistaken assumption that yaw and presession are part of the RPM threshold. I have made it quite clear in several posts, including a recent one to leftiye, that a seperate action causing the helical spiral when bullets go to sleep which is caused from yaw and precession. The seperate action of a cast bullet exceeding the RPM threshold and going into a helical spiral (or off on a complete tangent) is caused by the centrifugal force, not yaw and precession. The 1st results in the helical sprial getting smaller and going away and the 2nd (the thrux of the RPM threshold) causes the helical spiral to get larger in a non linear fashion. Seems to a simple layman like me that an aeronautical engineer would understand that 2 actions may seem similar yet are different actions because they are caused by different forces with end results being disimilar.

The fact that you do not care for the tone of (my) discussion, how (I) chose to argue (my) position, the aphysical wording of (my) theory, and desire to extrapolate it to different situations wrt caliber, load, bullet design, etc. (and you) don't consider (my) comments thus far to be responsive to (your) objections does not make them none the less factual. Considering you apparently disagree with the entire ballistcs communtiy perhaps you could enumerate on your own published ballistics works, books, articles or even thesis?

I agree it is best that we disengage on this topic. Since we obviously disagree on the basics of ballistic there won't be much useful to come out of further discussion. When you get your K-Hornet to put 10 shots in 1 moa or less at 100 and 200 yards with cast bullets (perhaps a more a realistic quantification of "varmint" accuracy than is 3 moa+) at 3000+ fps then I will come back in and congradualte you. Until then keep in mind that those pesky little flyers that both you and Dan are getting, perhaps, indeed are telling you something. Such uncalled flyers, even in insufficient samplings of 5 shots, should not be ignored. Good luck and good shooting to you.

I've some more HV cast bullet tests to run and will continue to post the results on this thread. I will be pushing that 12" twist M70 target rifle to see where the RPM threshold is with the 311466 and RL22 powder. I will also be conductiong some HV tests with my 14" twist Savage M40 22 Hornet using the 225438 and perhaps the 225107.

Larry Gibson

[shooter93]

Just as an aside....Precision Shooting ran a 2 part article written on bullet yaw and what the author really believes is happening.....he calls it coning... It's a very good read and he makes an exceptional case for it.....me...I'm just an idiot old shooter.

[felix]

It's just hard to see without resorting to multiple, stacked, targets. The groups should all show the same picture configuration but the center of group should be different for each target. The spiral should be evident. Egg shaped boolit holes should be ignored when there is significant wind. ... felix

[Larry Gibson]

It's just hard to see without resorting to multiple, stacked, targets. The groups should all show the same picture configuration but the center of group should be different for each target. The spiral should be evident. Egg shaped boolit holes should be ignored when there is significant wind. ... felix

The problem is finding a range where you can set the targets up with enough distance between them for the spiral to be evident. Might take more than 300 yards with some ammuntion.

Not quite sure why an additional test is needed if one simply tests at 100 ant 200 yards for linear or non linear expansion of the groups between the 2 ranges. That tells the tale rather simply. Considering in the last test I ran I shot 10 shot groups at 100 and 200 yards. With the 14" twist I shot a 1.5 moa group at 100 and 200 yards. with the same wind (1-2 mph out of 5 o'clock) using the same load in the 10" twist the 200 yardgroup was 14"+. It would have taken a 20+ mph wind change to switching from 3 o'clock to 9 o'clock to make that 14+"+ group. That did not happen.

Larry Gibson

[44man]

Smiths: 41 mag has the 18+ twist. The 44 has the 20 twist, Jim & Al. Positive. This was back with the dash 2s, anyway. I am assuming, Jim, you are using higher dash guns in the Smith line. ... felix
Our S&W's were early guns starting in 1956 to the 80's.
I do not know if twist rates were changed after.

[44man]

It's just hard to see without resorting to multiple, stacked, targets. The groups should all show the same picture configuration but the center of group should be different for each target. The spiral should be evident. Egg shaped boolit holes should be ignored when there is significant wind. ... felix
I don't know Felix. I have had to aim very far into the wind and never seen oblong holes. Keyholes are yaw and I have seen complete side hits at 50 yards.
There might be some up and down egg shaped holes at long range because the bullet tends to stay in a forward position in the arc and not follow it. That is very small and you might not be able to measure it.
Paper is very thin and any bullet that makes an out of round hole must be way out of line. That will NOT be a helix.

[felix]

Jim, stripping is the major cause of major egg-holes, and sometimes a complete projectile profile appears on paper. Minor egg-holes are barely noticeable and can be seen when a long projectile tilts INTO the wind for directional compensation, like an airplane. That minor tilt shows good adherence to the rifling. Switching winds make egg-holes with the major axis at random. ... felix

[Iron Mike Golf]

I don't know Felix. I have had to aim very far into the wind and never seen oblong holes. Keyholes are yaw and I have seen complete side hits at 50 yards...

Wouldn't tractibility apply to wind and spin drift just as it applies to gravity?