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joeb33050
11-25-2007, 12:55 PM
I read references to this, searched here and in the search sites without much result. Can someone tell me about this and maybe where I can read about it?
Thanks;
joe b.

Razor
11-25-2007, 04:09 PM
Yeah, someone please share your knowledge...
I been wonderin' too.

Razor

Junior1942
11-25-2007, 05:47 PM
If you'll look in the "Fouling Shot" at the equipment list for the nationals you'll find their twist and chrono velocity. It's a rare one which goes over 110,000 rpm. The high speed boys use 17 and 18 twist barrels for low rpms.

2750 fps @ 1 - 18 twist = 110,000 rpms.
1528 fps @ 1 - 10 twist = 110,016 rpms.

montana_charlie
11-25-2007, 09:44 PM
The only thing I know about "RPM" is a note in the FAQ section of one of the bullet maker's sites. The question was about why do .22 bullets fragment when fired. The answer was that a commercial bullet (80 grain?) fired in a military barrel rifled for the FMJ Ball (62 grain?) would fly apart. Apparently it's common knowledge among bullet companies.

As for the rest of the "RPM" subject, I am totally ignorant...
and might even prefer to stay that way.
CM

shooter93
11-25-2007, 09:47 PM
Can someone post the formula to calculate rpm's when you know the velocity and twist rate? Thanks.

Nueces
11-25-2007, 10:00 PM
If S = speed, in feet per second and T = rifling twist in inches, then bullet rpm is:

720 x S/T in revs per minute.

Mark

Larry Gibson
11-25-2007, 10:36 PM
The RPM threshold is area of velocity where the RPM created by the twist accentuates the defects in cast bullets creating excessive yaw, wobble and pitch of the bullet during flight. Defects in cast bullets are caused by imbalance due to out of round casting, other casting defects, or unwanted obturation during acceleration. Exactly where that threshold is depends on numerous things but those that mostly affect the threshold are; burning rate of powder, quality of cast bullet, design of cast bullet, alloy, fit of bullet to throat/leade and twist of the rifling. I've found over the years that with normal commercial moulds generally available (what most of us use), casting quality bullets of WWs or harder, with proper lube and fit to the throat when using medium to slow burning powders the threshold is in the 125-140,000 RPM range. If we are using the old '06 with a 10" twist and 311291 then the threshold translates to somewhere between 1735 fps and 1944 fps we will find the best accuracy when using 4895 or a slower burning powder.

With a faster powder such as 2400 best accuracy will come at a little slower velocity as the faster powder has a faster acceleration. This means unwanted obturation will occur at lower velocity so accuracy will deteriorate quicker than when the medium/slower powders are used.

The cast bullet bench rest boys really slow twists down which does help considerable. If one is building a special purpose cast bullet rifle then twist is of major importance. My 14" twist Palma barrel (27.5" long) in .308 Winchester shoots regular cast bullets (30-15--FN, 311291, 311041, 311299) with excellent accuracy in the 2400+ fps which is 125,000 RPM, right at the beginning of the threshold. Really, really best accuracy comes down in the 21-2200 fps range which is around the 110,000 RPM area Junior1942 talks about. Same bullets in my M70 target with 12" twist 26" barrel loose accuracy at the same RPM as the 14" twist barrel. My M788 with a 10" twist 22" barrel does exactly the same. With the 12" twist that is in the 21-2200 fps range and with the 10" twist it is in the 1740-1940 fps range.

I've found that most regular heavy for caliber cast bullets shot out of regular rifles shoot best in the 125-140,000 RPM range with medium to slow powders. One merely must know the twist of the rifle to figure what the velocity range for best accuracy will be.

Buckshot
11-25-2007, 11:47 PM
............As an aside but also tied to RPM's is people's (especially the media and polititions) is the belief that the bullet in flight is like a buzzsaw. The big whoorah orver Winchester's original "Black Talon" (ooooh, nasty BAD bullets) with their engineered expansion characteristics had them compared to that buzzsaw turned loose inside someone. I believe it was also this concept that had Janet Reno exclain that the industry needed to develop less lethal bullets. What a bonehead.

The fact is that a bullet or boolit in flight spins at the same rotational speed in forward progression as that imparted by the twist of the barrel. A 10" twist imparts one complete rotation per each 10" of forward motion. An object 16" thick would see 1/2 a rotation of the bullet fired from a 444 Marlin with it's 38" twist.

The image of a slug spinning at 110,000 rpm and expanding as it passes through an object certainly would mess things up. However that 'thing' would have to be 22.7 miles thick to see all 110,000 of those revolutions.

.................Buckshot

wills
11-26-2007, 12:08 AM
Lot of drop in those 22.7 miles.

Bret4207
11-26-2007, 06:30 AM
I think in light of some of the work done by members here we might better call it the "RPM threshold THEORY". It's no more fact than man made global warming or the Easter Bunny from what I see reported. There are of course limits to everything.

joeb33050
11-26-2007, 07:09 AM
I think in light of some of the work done by members here we might better call it the "RPM threshold THEORY". It's no more fact than man made global warming or the Easter Bunny from what I see reported. There are of course limits to everything.

What do you mean about the Easter Bunny??? What are you suggesting??? Who else could leave those eggs? Next you'll say something about Santa!
joe b.

Junior1942
11-26-2007, 10:20 AM
I think in light of some of the work done by members here we might better call it the "RPM threshold THEORY". It's no more fact than man made global warming or the Easter Bunny from what I see reported. There are of course limits to everything.I'll go with "theory." I started thinking about rpms when I wondered why my Turk Mauser would shoot jacketed bullets 1 MOA or less at 2400 fps, and the Lyman #323471 wouldn't go 1 MOA at over 1400 fps. I wanted to get 1800 fps minimun for deer hunting with it. But, no, at 1700 - 1800 fps it wanted to put 2 almost touching and 1 out at the edge of the target.

Then I got to wondering why the hole out at the edge of the target usually had a comma on it. Then I got to computing my Turk's rpms and comparing those data with data from the "Fouling Shot's" equipment list. Then, obviously, my commas were the bullets coming apart.

I also agree with Larry in that each rifle and alloy are subject to their own peculiarities. My 1 - 9.5 twist SKS, for example, shoots the 311041 at 1700 fps, 128842 rpms, just fine and dandy.

45 2.1
11-26-2007, 10:27 AM
The RPM threshold is area of velocity where the RPM created by the twist accentuates the defects in cast bullets creating excessive yaw, wobble and pitch of the bullet during flight. Defects in cast bullets are caused by imbalance due to out of round casting, other casting defects, or unwanted obturation during acceleration.

Hmm, I would think you would have added: imballanced boolits that were shoved out of line by being undersize, too hard or soft for their size and load intensity, wrong powder causing improper balistics, boolits that were not fitted to the controlling area in the case neck, throat and rifling origin among several other things. The main thought is that at a certain RPM, the defects mentioned above allow the centrifigal force to overwhelm the stability of the boolit. The above symtoms are things that the loader introduces into the cartridge and these items can be overcome. The problem here is one of a symtom being thought of as a theory.

Shiloh
11-26-2007, 11:07 AM
Is projectile weight part of the equation?? What about boolit length?? The RPM wouldn't change no matter what, but is a short boolit affected more than a long one or vice versa??

In other words, does the RPM threshold theory/affect kick in at different velocities for different boolits?

Thanks folks,

Shiloh :castmine:

felix
11-26-2007, 11:54 AM
Shiloh, yes indeed! Not weight per se, but projectile toughness (uniformity in springback). Things get a lot more OUT of sync as the boolit diameter increases, not as much as the length increases, and more IN sync as the boolit is hollowed out. There is no such thing as a perfectly cast-ed boolit, perfectly sized boolit as per Bob's and Larry's statements. We are just plain lucky that cast boolits can be made to shoot as good as they do per gun style/sport application. ... felix

Larry Gibson
11-26-2007, 01:29 PM
45 2.1

"Hmm, I would think you would have added: imballanced boolits that were shoved out of line by being undersize, too hard or soft for their size and load intensity,"

That is "unwanted obturation".

"wrong powder causing improper balistics,"

Thought that was covered under the explanation of fast vs medium/slow powders effect on obturaration during accelleration. I'm sure a lengthy treatise could be written on the subject or "theory".

"boolits that were not fitted to the controlling area in the case neck, throat and rifling origin among several other things"

Thought I mentioned that with; "fit of bullet to throat/leade and twist of the rifling".

"The main thought is that at a certain RPM, the defects mentioned above allow the centrifigal force to overwhelm the stability of the boolit. The above symtoms are things that the loader introduces into the cartridge and these items can be overcome. The problem here is one of a symtom being thought of as a theory"

Well I don't believe they are "symptoms". The RPM threshold ("theory" if you will) holds pretty much true with the commercillay available moulds (Lyman, Lee, RCBS, Saeco) of normal design that most of us cast bullets from. I have repeatidly stated that. The fact that Bass can get his cast bullet from a custom made mould to shoot well at 2500+ fps out of a 10" twist '06 does not do anyone else any good who wants to get a 311291 to shoot well above 2000 fps in there 10" twist '06. I have shot Bass's bullets with his loading techniques and I do get decent accuracy at 2500 fps BUT the most accurate loads with that bullet are down within the RPM threshold. That is fact, not theory. Same with Starmetal and his 6.5 AR. No one else gets up into the 2400+ fps range with any accuracy what so ever including you. I also have used your loading technique for the 6.5 Swede (we discussed it by PM and on the phone if you remember) and our results were pretty much the same.

As to the RPM threshold being theory; If it is theory then why do the bench resters use custom made barrels with slow twists to cut down on RPM? Why don't they just use the faster twists that HP shooters use? Those faster twist barrels are pretty darn accurate with J bullets, aren't they? Why is it that the best accuracy with ANY rifle using regular cast bullets is going to be below or in the RPM threshold and not above it? Yes there is lots of well proven reasons why the RPM threshold is fact not theory.

How many of you have ANY cast bullet load that gives the BEST accuracy that rifle is capable of with that bullet that is cranking over 140,000 RPM?

Larry Gibson

Bret4207
11-26-2007, 02:00 PM
Larry, I mean no offense, it's just the more things we seem to take as fact with cast seem to have exceptions these days. Why I don't know, it just seems that the more we strive for repeatable "scientific" answers to cast issues, the more it seems this is an art and that some guys manage to break the "rules".

floodgate
11-26-2007, 02:28 PM
joeb...:

And I WISH they'd knock off that "Global" warming junk; all it is is flack promoting the "Round Earth" myth!

floosfate

Larry Gibson
11-26-2007, 02:28 PM
Bret

I take no offense. Yes, there are sometimes exceptions to the rules but when we really look at them we find the exception really isn't there. A good example is the discusion going on regarding the .22 Hornet at 2800 fps. Sounds impressive doesn't it? We might even think of that as an exception to the RPM threshold might we? However when we look closely we find the Hornet probably has a 16" twist and at 2800 fps the RPM is 126,031, just at the begining of the threshold. And if we read the post closely we find that best accuracy comes at a much lower velocity and thus lower RPM also. So, in reality, it is not an exception.

They are also talking the speed one can get with the .222 and that is true, been there done that. However, again if we look close the .222 will no doubt have a 14" twist and 2800 fps is 144,000 RPM. A good Lovern design bullet as they are talking will creep up to that and maybe beyond with reasonable accuracy. You can go much higher in velocity but not with good accuracy. Again, best accuracy with the .222 will be within the RPM threshold.

I believe the scientific "repeatability" of the RPM threshold is self evident. As I asked; how many of us have a regular cast bullet load that gives it's best accuracy above the RPM threshold?

Larry Gibson

45 2.1
11-26-2007, 04:08 PM
I believe the scientific "repeatability" of the RPM threshold is self evident. As I asked; how many of us have a regular cast bullet load that gives it's best accuracy above the RPM threshold? Larry Gibson

Larry, you can believe whatever you want. There have been quite a few people publish articles shooting boolits in 10" or 12" twists well over 2600 fps with under MOA accuracy in commercial rifles and standard boolit molds. Not really hard to do either. Several of the CBA crowd have done it also at one time or another, but thats not what they're about. I suggest you write this up for publication in Joe's new book. Please make sure your name is attached to it. I want you to have all the credit for this.

Bass Ackward
11-26-2007, 04:17 PM
When I was going for Dan's 200,000 RPM contest, I got three successive groups of 1 1/4" to 1 3/4" groups. That was with a Lyman 311440HP mold at 2790 fps. That's 200,000 RPM. But I was not down to Dan's 1" requirement, so I lost.

But I have shot jacketed groups at that velocity that on average were not much better either. That is a factory mold in a factory gun and the holes were round with no do hickeys, tails, and none of the bullets bent or boomeranged back to me either. Does that mean it won't happen to some people? No. Just find out why.

Again: If one guy can do it, then there is a logical reason for any limitation. You have two choices. Ask why, and seek the answer. Or be happy with life and stare at the RPM chart.

Neither choice is wrong. :grin:

leftiye
11-26-2007, 04:39 PM
I have no dog in this fight -as they say. The dog I do have is a PITA anyway. I don't exactly know how to say this, so bear with me. I believe there is something to Larry's theory about RPMs. Even those who might be called "detractors" stipulate to the probability (you'd be foolish not to) of flaws and damage to bullets becoming more critical as rpm increases. Let's not forget that EVERYTHING is becoming more critical as velocity increases and not blame it all on high rpms. The environment in all of its aspects becomes more unfriendly for a soft lead boolit as speed increases.

Larry Gibson
11-26-2007, 11:25 PM
45 2.1

"There have been quite a few people publish articles shooting boolits in 10" or 12" twists well over 2600 fps with under MOA accuracy in commercial rifles and standard boolit molds. Not really hard to do either."

I'm more than happy to continue my learning. Could you reference the publications and dates where I can read said articles? As to not "not really hard to do" then I wonder why so many experienced cast bullet shooters can't do it.

"I suggest you write this up for publication in Joe's new book. Please make sure your name is attached to it. I want you to have all the credit for this."

I'd probably do that except I'm not the one who thought it up.

Larry Gibson

Larry Gibson
11-26-2007, 11:48 PM
Bass

As I recall Dan's test was for 5 consecutive 5 shot goups of MOA or less at 200,000 RPM. No one claimed his prize of a free mould. I've also shot nice "back to back groups" at high velocity but then it goes bad. What happened to the other two groups? I'll also ask how well that bullet shoots in that rifle at lower velocity within or under the RPM threshold? My reason for the question is I continually say the RPM threshold applies to the best accuracy and cast bullet is capable of in a rifle, not acceptable accuracy at higher velocity. Hell, today I pushed the GB C312-150-FN cast of ACWWs to 2600 fps in my Palma. That's 133,790 RPM BTW. I got a few good groups under 2" along the way but the last one at 2600 fps was a 4" group. All the holes were nice and round and it "held paper" but is that acceptable? Of course its not because that rifle will shoot close to MOA with other bullets at that velocity. I'm casting some of harder alloy as soon as I'm done here. I'm looking for a 1 to 1 1/2 MOA load with that bullet in the 2400+ fps range for shooting rock chucks out to 300 yards.

Larry Gibson

andrew375
11-27-2007, 05:04 AM
Well, I'm geting consistent sub moa accuracy with bullets doing 190,000+ RPM. This is with the NEI .224-72gr. in my 1 in 9" Savage.:-D

Bret4207
11-27-2007, 06:26 AM
I believe that at some point a boolit will more or less "vaporize" if subjected to enough RPM. Finding that point isn't something I'm interested in other than in the theory end of things. That being said, I find the experimentation fasinating.

45 2.1
11-27-2007, 07:43 AM
I'm more than happy to continue my learning. Could you reference the publications and dates where I can read said articles? As to not "not really hard to do" then I wonder why so many experienced cast bullet shooters can't do it.

Put out by Wolfe, the publishers of "Rifle and Handloader" back in the 80's or so, out of print. Don't remember its name, but it had a gray cover and was a compilation of articles from the magazines.

Most any high intensity 22 varmint cartridge will do this. I have seen quite a few post about this here. You might contact them to find out how.

As far as why so many experienced cast boolit shooters can't do it, read my tag line.

Bass Ackward
11-27-2007, 08:35 AM
Bass

As I recall Dan's test was for 5 consecutive 5 shot groups of MOA or less at 200,000 RPM. What happened to the other two groups? I'll also ask how well that bullet shoots in that rifle at lower velocity within or under the RPM threshold? Larry Gibson

Larry and All,

Take a deep breath and don't look at this as an attack. It's really for everyone, but I am going to answer your questions too, so it is addressed to you.

As you said, Dan wanted 5, 5 shot groups. The shells were already loaded. I would have had to mold and load more to finish the last 2 groups and the first 5 of that box were squibs for barrel preppers. (clean bore) So three groups was enough to tell me I couldn't do it. And that was the best accuracy I had obtained with that 311440 bullet in this 06. It was simply another light bullet for me to try.

Think pressure. If I wanted to continue to shoot it my style, I would needed a larger capacity case than an 06 and a longer barrel. (extend the pressure curve to raise velocity) (shorter throat too maybe) If I wanted to shoot a heavier bullet at low pressure, I would need more case capacity. So over bore, magnum cartridges make BETTER HV cast guns than standard calibers with this low pressure technique. So .... what makes a good low velocity cast cartridge is different from a HV requirement.

BIG POINT! RPM ceilings will be different based on case capacity and barrel length. A 308 is a better low velocity cast gun, but a 300 H&H would be a better HV cast gun on the same barrel. And if that 300 H&H has a 26" tube, it will have a higher RPM ceiling than an 18" job.


Main point:

Best accuracy with most firearms (always exceptions) and any bullet material is going to be at low velocity. Low velocity = low pressure. Low pressure = low friction. Low friction = low metal fouling, low barrel heat, low barrel vibration. No need for heavy barrels or bedding issues or a long list of stuff. Less recoil too.

Now, try shooting 5, 10 shot jacketed bullet groups at high and a good low velocity load without cleaning. See if your "best accuracy" with jacketed isn't better at low velocity. RPMs .... or pressure? See if your groups don't look more like cast groups too, fliers and all. :grin:

Look at military rifle research and design. Why do you think military groove diameters are usually so generous? To allow for accuracy with high shot strings between cleanings! To cut pressure and friction. That's why military rifles aren't free floated either. Control that barrel when vibration DOES become a problem. German's had steps to do the same thing and barrel bands. So military organizations around the world came to the same conclusion on harmonics / control. You don't have as much harmonics at low velocity.

Now, think about this very closely. If I took 5 different jacketed bullets of 150 grains for HV use. Some would shoot better than others in my gun. Do you agree? My gun can be a sub MOA with one design and an 1 1/2"er with another. Is that the coppers fault? We don't blame jacketed bullet brands for being more susceptible to RPMs now do we? And who simply buys and tests only one jacketed bullet in his gun if he is serious about accuracy? Does my best one mean it will be your best one?

Why then do we insist that every cast bullet design must be capable of high RPM (velocity) accuracy? And when it isn't, we blame the lead. You already KNOW cast is more .... finicky to fouling than jacketed at any velocity. Therefore, if there is a difference between 5 different jacketed bullets performance at HV, then it stands to reason that there would be a BIGGER difference between 5 lead bullet designs performance. Logical huh? And the performance would be different for me than it would be for you, wouldn't it? Explains your use of my bullets now don't it? All you may need is a different diameter from mine. Coarse, it could be the same at low velocity too, but down there at those levels, we think that's normal. And then how many people try just one cast bullet in a gun for HV before they subscribe to the RPM theory? But your straight sided, sharper shouldered 308 case design will never be better for HV cast than my sloping and tapered 30-06 that burns powder more slowly and uses the column as a filler.

Back to .... the "best accuracy" statement for cast. It's really the best "low velocity" accuracy for guns in general then huh? It has a lot to do with our ability to shoot those guns too huh? Has little to do with bullets of any material unless what we or the gun does to them, causes problems like tails, hooks, or bending. So the RPM theory is really a "rifled barrel" theory, not just a bullet or cast one and bullet fit is critical for all bullet materials. A slower twist rate throws less pressure, has less friction and heat, and therefore less vibration. All more cast friendly elements and why lead performs better. Pressure. Not RPMs. (Catch that Junior)

Take your time and read this through again as it is my last attempt. I have said all there is to say without beating it all to death. And since "pressure" is my theory and can't be proved, it's no more provable than your RPM theory. Believe what you want to believe. But if you work with a pressure ceiling, you will find far more answers than if you go at it from an RPM standpoint.

Bret4207
11-27-2007, 10:09 AM
[QUOTE=45 2.1;250723Put out by Wolfe, the publishers of "Rifle and Handloader" back in the 80's or so, out of print. Don't remember its name, but it had a gray cover and was a compilation of articles from the magazines.

.[/QUOTE]


The Art of Bullet Casting?

Bass Ackward
11-27-2007, 11:01 AM
Well, I'm geting consistent sub moa accuracy with bullets doing 190,000+ RPM. This is with the NEI .224-72gr. in my 1 in 9" Savage.:-D


Thanks, Andy. The more people speak up the better the statistics for those that have the BS flag in hand.

What powder? 4831?

felix
11-27-2007, 11:18 AM
The problem here is trying to determine which variables are independent of one another for maximizing/minimizing something. From this conversation it is apparent that we are trying to maximize RPM while at the same time minimizing group size. Here is where the proverbial cluster analysis of all the variables, independent and dependent, are grouped into one space to display the shape and density of the cloud of data points. Yes, JoeB and Maven, I have to bow to you both in this instance, in that statistics is hereby needed big time. The objective of this study would be to determine which variables are actually independent on one another so that they can be controlled to optimize the path towards realizing the two "goals". On the other hand, when trying to optimize only one of the two goals the problem becomes much more manageable, if not more realistic. ... felix

Larry Gibson
11-27-2007, 01:01 PM
Well, I'm geting consistent sub moa accuracy with bullets doing 190,000+ RPM. This is with the NEI .224-72gr. in my 1 in 9" Savage.:-D


Kindly show us pictures of the groups (if available) and load data so we may codgitate on it. Thank you.

Larry Gibson

Larry Gibson
11-27-2007, 01:36 PM
Bass

The question goes like this; "Why can I get the same accuracy as I get out of my '06 with 311291 at higher velocity, like at 2400 fps, than I get at 1850 fps?"

In other words we are not talking different bullets, different barrel lengths, different cartridges or different twists. What we're talking about is that guy, or any guy, is not going to get the same accuracy at 2400+ fps with a 311291 out of a 10" twist '06 that they get at 1850 fps. Now if the guy is getting 1 1/2" groups at 1850 fps he can shoot so boosting the velocity and being inaccurate does not mean it's the guy who can't shoot. The reason for the inaccuracy is RPM.

You dance around the answer with your dissertaion on lower velocity means lower pressure which you say means better accuracy. That is very seldom true with jacketed bullets as best accuracy comes with efficient shot to shot ignition of the powder. It can be had, with most any rifle, at low velocity, medium velocity or high velocity. Those ranges of velocities depend on the cartridge of course. I believe most here know it.

But to the point; lower velocity mean lower RPM with a given barrel twist. Pretty simple isn't it. Shoot the same cast bullet loads in rifles of 10, 12 and 14" twists and you will see that the slower the twist the better the accuracy. Now please don't tell me that the pressure is different in the different twists. The difference in pressure between those twists falls within shot to shot variation which means it is essentially the same. Even if you vary the pressure with slower powders the accuracy deteriorates within the same RPM threshold in each of the barrels.

RPM effects jacketed bullets the same as it does cast bullets. The inaccuracy is just not as noticeable because most JBs are made quite well and they do not suffer the adverse obturation during acceleration that cast bullets do. Yes jacketed bullets can be pushed to far too but that's another dissertation. If you remember the reason for the slower twists with Palma barrels in 7.62 is that service ammo was required. The slower twists give less RPM to the 145-155 gr ball bullets and the imbalances (defects) are not as accentuated. Inshooting service issue ammo they could not vary the loads. They could vary the twist and lower the RPM. That reduction of RPM greatly improved the accuracy of the service 7.62 ammo. It is the very same thing with cast bullets. If you want to drive them fast then lower the RPM.

Higher RPM accentuates the imbalances of the cast bullets which causes less accuracy. To get the best accuracy at higher velocity you must change the RPM by going to a slower twist. If not then your best accuracy will not come above the RPM threshold.

Larry Gibson

Idaho Sharpshooter
11-27-2007, 01:43 PM
45-2.1,

that is the beauty of this forum, you can support (or not) any theory that comes down the road.
But, when the umpire says "strike three..." Mighty Casey has struck out! The RPM threshold computations and testing protocols were ones done at great taxpayer expense at Picatinny Arsenal several years ago. That data was adopted by Sierra and is shown as their information supporting the fact that bullet MV provides up to three separate ballistic coefficients as the bullet moves and slows down. One of the other things they got was that the decay rate of the spin changes less than one-percent over the course of the bullet's flight.

For those (like me) challenged by Quantum Mechanics and String Theory, the simple answer is: take a soda can and draw a circle that size on a piece of paper. Draw lines up & down and left to right, like crosshairs on a rifle scope. Where the NS and WE lines intersect is the actual geometric center of that bullet. Call it C1. Next make a dot, say .002" away from the center crosshairs. Imagine that dot is a microscopic void in the bullet. Call it C2. 180-degrees away from that void is the center of gravity, call it CG.

Step Two: take a rifle barrel chambered in, say 308W, with a 1:12" twist. That twist barrel will provide that bullets 1RPR (revolution per rotation) every 12" inside the barrel. Shoot that bullet at 3,000fps. At exit that bullet is traveling that speed and rotating at

Let me call my friend at Sierra and get the exact formula phrasing.

Rich

Here we goes; that bullet is traveling 3,000fps and revolving at 1rps. Multiply the speed times the rps and then multiply that times 60 (seconds per minute). 1x3,000= 3,000 x 60 = 180,000rpm. Once the projectile leaves the confines of the barrel C2 and CG come into conflict. Each wants to be the center that the projectile rotates around. That can't happen. The projectile begins to rotate back and forth on it axis trying to center both at the same time. So, about 180,00 times per minute the projectile yaws back and forth the distance between the two centers. Visualize a minute hand on a clock constantly moving between 10am and 10:00:01am...180,000 times a minute. That movement is what causes the bullet to yaw off course in a random pattern, and adds to the droop gravity is causing. The bullet may be structurally sound enough to endure that for the several 1,000ths of a second it takes to get to the 100yd target. Exaggerate the the difference between C1 and C2 and CG enough and the projectile fails.

felix
11-27-2007, 02:10 PM
Larry and John, I think you both are really saying the same thing in a round-about-way. Pressure, with land acquisition especially, destroys boolits more than bullets, making the RPM factor much more paramount. I wish there was a good way to measure the pressure curve, projectile deformation, and muzzle deflection simultaneously at each milli/micro-second level. Something like what the oil finders do daily with their geophones (multiple microphones and explosives), and the medical folks do with their magnetic wave shooters and re-capturing devices. ... felix

felix
11-27-2007, 02:18 PM
IS, the question is not how much the rotational speed slows, but how the boolit acquired that rotational speed and it's effect on the pressure curve and muzzle dynamics. Yes, we must include all of the known measurements for that barrel in question to be able to decipher their effects in detail. ... felix

joeb33050
11-27-2007, 02:56 PM
I went through the CBA 2006 National Match results, made a spreadsheet showing the TWIST, MV and RPM of the entrant's guns.
Taking out those with gain twist, then the SS Breech Seaters, the RPM varied from 158,400 down to 96075, with an average of 125578.
The workbook is attached. Would someone translate so it can be shown here?

There's a lot on the 30BR and short bullets and slow twists at http://www.6mmbr.com/30BR.html

I suspect that short light bullets are easier to shoot accurately, hence the references to 100-125 grain .30 caliber bullets.

Greenhill says that in 30 caliber, a 10" twist will stabilize a bullet 1.42" long, which would weigh ~250 grains. It says that a 15" twist, for examploe, will stabilize a bullet .95" long weighing ~166 grains. All Cast bullets.
I think it's clear that 30 caliber twists are generally "faster than needed", that slower twists with shorter lighter bullets are easier to shoot and torque on the bags less.
My impression is that gain twist and slow twist barrels are "easier on the bullet" as the bullet accelerates in rotation.

joe b.

Junior1942
11-27-2007, 03:10 PM
Joe, take out the ones with estimated velocities. Use only the ones with chronographed velocities.

Bass Ackward
11-27-2007, 04:09 PM
Even if you vary the pressure with slower powders the accuracy deteriorates within the same RPM threshold in each of the barrels.
Larry Gibson

No sir. Not in any gun I ever shot cast in.

The barrel provides the accuracy. Twist rate is a "maximum" bullet weight and range distance related factor for stability. Bedding and barrel dimensions control the harmonics. If you can't build a rifle to control the harmonics, you must slow the twist rate.

The 8.66 twist, 7MMs favorite bullet was the 115 grain Speer with 45.5 to 46.5 grains of 4064 in all of them. Trick was that you had to bed them with enough tip pressure to control the vibration.

Larry Gibson
11-27-2007, 05:02 PM
Bass

The harmonics of the barrel have absolutely nothing to do with the defects in cast bullets as we cast them or the defects (unwanted obturation) caused by accelleration. It is those defects that are accentuated by RPM and cause inaccuracy in the exterior ballistics portion of the bullets flight. I''ve not found harmonics to play that much of a role in accuracy. A good barrel that is free floated will shoot well. Good harmonics of a barrel are directly tied to consistant ignition and burning of the powder. That translates in consitant movement of the bullet down the barrel shot to shot. That means the vibrations (harmonics) of the barrel are also consistant shot to shot. A barrel doesn't have its own harmonics as such. Consistant loads make for consistant harmonics in the barrel. Velocity is imaterial to consistant harmonics.

As to if I can't build a rifle some would consider that a cop out on your part if you infer only custom guns shoot cast bullets fast and accurately. I am saying the RPM threshold holds to any rifle, custom, factory or military.

I've absolutely no idea what the 7mm with the Speer J bullets has to do with this thread.

Larry Gibson

Bass Ackward
11-27-2007, 06:05 PM
Bass

The harmonics of the barrel have absolutely nothing to do with the defects in cast bullets as we cast them or the defects (unwanted obturation) caused by accelleration. Larry Gibson


Larry,

I bought Veral Smiths little Blue book that has cost me several thousands of dollars to date. My first purchase was a 700 Remington LSS in 30-06. First thing I did was to free float it. Next thing I did was try to shoot high velocity cast in it and I stuck the bolt. 300 rounds later I started HV work again.

I used the 56 grains of RL 19 that I always quote as this is where groups peaked. Group sizes were about 2 " with defective fliers running out to 6". So I bedded it with 2# of pressure. Groups came in a little to let's call it 1 3/4" and fliers stayed about 6". I upped the pressure to 4#. This time groups stayed the same and fliers came in @ 4". Hmmmm I says. So I upped the pressure to 8#. Groups came right in to about an inch and fliers now are 1 1/2". That's a bullet with the grand canyon running up the side.

My "guess" is that a bad bullet or load causes a rotational change that alters timing and that change alters barrel vibration causing the bullet to exit at wild points. Uncontrolled, that vibration is going to get worse the higher the velocity goes. Bedding pressure minimizes that effect. The only time I get truly wild fliers now is when my lube thickens and sizes down my bullets enough that they DO let go of the rifling. Then every shot is a flier, good bullets and all. But based upon my results above, I disagree that bad or unbalanced bullets are the cause of most fliers. Otherwise bedding would show no change.

MOST of all cast bullet damage is done from internal ballistics while the bullet is still in the barrel, and not from external ballistics at least until longer range. Even at high RPM.

Idaho Sharpshooter
11-27-2007, 08:56 PM
Actually, everything we do to a cast boolit after it falls from the mould onto a terry cloth pad is bad for it. One reason the breech seater boys shoot so well, is they do nothing to the bullet until they seat it into the barrel with a .0003"-.0005" interference fit that has the effect of sealing the the bullet off from ignition gasses and causing deformation as the bullet obdurates to fill a throat and then pressure swages back down to fit the rifling. Their bullets are pre-obdurated, for lack of a more precise scientific term. Their bullets are also softer, which would allow a smaller void to be swaged closed inside the barrel. J-bullets are swaged twice or three times in the forming process...which pretty well swages any imperfections, occlusions, whatever term you prefer; out. Plus that copper skin is about 100Bhn, and they are always swaging an increase is diameter which helps.

Rich

felix
11-27-2007, 09:35 PM
Rich, what you are saying is fine, but pay attention to these definitions:

1. ob·tu·rate: To close or obstruct.

2. ob·du·rate: Not giving in to persuasion; intractable.
Synonym: inflexible.


... felix

AnthonyB
11-27-2007, 09:40 PM
Guys, this is a fascinating thread. Please don't let the different opinions halt the discussion.
Tony

Rrusse11
11-27-2007, 10:18 PM
Guys, this is a fascinating thread. Please don't let the different opinions halt the discussion.
Tony
I'll second that! :)
My 2 cents; handmade cast boolits can rarely be as consistent as swaged/jacketed, lower rpms and slower powders mean less centrifugal deviation for cast. My slow twist 444 and 454 Colt Marlins have a speed/RPM threshold with heavy boolits that is clear. Never tried to test the upper end.
Cheers,
R*2

Larry Gibson
11-28-2007, 12:21 AM
Bass

Whens the last time you EVER saw a bench rest rifle with fore end pressure on the barrel, even cast bullet bench rest rifles? If what you say is correct then all of them ould have pressure on the barrel instead of none of them. Those boys shoot to win. If it works they use it, if it doesn't they don't. The only time I've seen or heard of pressure on the barrel helping accuracy is with bad barrels or really light weight ones. There are muzzle attachments that tune the harmonics to the load or you can tune the load to the harmonics. However, good barrels shoot well without either when consistant loads are used. Had a fellow HP shooter who had a target rifle (6.5-308) that shot 1/2 MOA with MKs. He thought if he put a Browning Boss on it he could get 1/4 MOA so he had one put on. Well he tuned and tuned and tuned and couldn't get the Boss equiped barrel to shoot under 1 moa. Took the Boss of and it shot 1/2 MOA again. So does this one incident mean the Boss doesn't work? No, it just means that good barrels shoot well and in this case the Boss did not lesson the harmonics but increased them.

If you can keep a bullet with a "grand canyon running up the side" from being a flyer just by applying pressure to the barrel then you must part your hair in the right spot. I'd think you be too busy doing that magic (and making a fortune) to all the bench rest rifles and match rifles out there to be discussing this with me. But let us continue our conversation anyway.

"MOST of all cast bullet damage is done from internal ballistics while the bullet is still in the barrel, and not from external ballistics at least until longer range. Even at high RPM."

Bass, now when have I EVER said RPM damages the bullet? I haven't, and at normal velocity I don't think it will unless there is a gross defect in the bullet from some other reason. Of course the damage to a bullet is done in the barrel, that's called obturation. Obturation can be good or it can be bad but most obturation is bad because it creates inbalances in the bullet. The inbalance means the center of gravity does not coincide with the center of form. While in the barrel the bullet rotates (regardless of the twist) around the center of form. When the bullet exite the barrel the bullet rotates around the center of gravity. If the two do not coincide the bullet is inbalanced. It is during the external ballistics (that's outside the barrel) that RPM accentuates the inbalances creating yaw, pitch and wobble. The centrifical force created by the higher RPM causes the yaw, pitch and wobble to be worse the higher the RPM is. This translates into larger dispersion or larger groups. There is a very good description of this (pictures too) on pages 16-19 in Hornady's Fourth edition, Vol 1 reloading manual. Pressure on the barrel will have no effect on how the centrifical force causes this dispersion during the bullet during it's flight.

I shot your bullets too in a 30-06 rifle with 10" twist that is MOA capable with several loads both jacketed and cast. Using your load of 56 gr RL19 (actually worked up from 54 through 58 gr) and groups ran from 2.4 to 14". Most were in the 3-4" range. I actually got better accuracy with H4831SC of 2-3" groups in the 22-2350 fps range. But guess what? I also shot your bullet over 27 gr of 4895 (that's my accuracy load with the Lee C312-155-R). Your 154 gr LBT bullets ran 1905 fps/137,160 RPM and went into .98" (call it 1"). So what's that prove? Nothing much except your bullet shoots much more accurately down in the RPM threshold. That is just what I have been saying.

So, yes I can get "reasonable" accuracy of 2-4" (if we call that "reasonable" with a MOA capable rifle) at a higher velocity of 2000-2400 fps with your bullet and your load. However, best accuracy of MOA (consistant accuracy also) comes in or under the RPM threshold. The higher the velocity the higher the RPM and the larger the groups. Not to hard to understand.

Larry Gibson

joeb33050
11-28-2007, 06:37 AM
Joe, take out the ones with estimated velocities. Use only the ones with chronographed velocities.

There's a column on the sheet that's either C = chronographed, or E = estimated. I wish somebody would put this up, here.
joe b.

Pat I.
11-28-2007, 06:56 AM
It seems as if this topic could go on forever with no agreement but I think if we look at what jacketed BR shooters are using for bullets it takes the theory out of the equation. The bullets they use are made on J4 jackets which have .0002 run out on the jackets compared to maybe .0005 with factory jackets. The reason they use them is to keep the CG and the center of form as close together as possible to maximize balance. It has nothing to do with internal ballistics and is all about the bullet once it leaves the barrel.

I suppose it might be possible to attain usable accuracy with a cast bullet at speed but I'd be willing to bet that in most if not all instances best accuracy will be found by following the basic principal of an RPM threshold and I also believe it could be predicted for twist rate and caliber with a little study. It has nothing to do with the bullet vaporizing or anything else, it's all about velocity and spin rate accentuating the imbalances built into cast bullets by design.

My 2 cents.

Pat

45 2.1
11-28-2007, 07:54 AM
Rich-
The government does fine work, usually to prove a point and isn't shy about throwing money at things. The point is they didn't do that work with a bunch of cast boolits though. I've seen enough things that those ideas don't explain to know that it's only a theory. Until a theory explains everything and is repeatedly provable, it's only a theory and not a law. Too many articles busting it have been published besides the things i've done and seen for me to accept it covering everything. Too much smaller caliber work going on for a long time that is repeatable to believe RPM theory.

This RPM theory thing seems to be evolving before our eyes as the parameters change with every post.

felix
11-28-2007, 09:14 AM
Everything is RPM limited, depending on its mass construction and its diameter. ... felix

Idaho Sharpshooter
11-28-2007, 12:10 PM
45-2.1,

until I built my 22-378 Wbee Ackley Improved I would have agreed with you. But, since I was able to blow up every bullet I was offered with enough speed; and that case could hold enough powder to do so, I have to stick with what the arsenal and my personal testing has shown me.

Going to the .223 as a primary infantryman's weapon back in the 1960's may make more sense today in light of the RPM issues. Small caliber, and heavy for caliber bullets = fast(er) twist. Faster twist and 3,000+fps MV = lots of RPM. Minute %-age of spin rate decay = increased radial/axial tissue displacement on impact.

Rich

Larry Gibson
11-28-2007, 12:27 PM
I copied Buckshot's response on another thread here because it's a classic example of the effects of the RPM Threshold and gives a good view as how it is misunderstood.

"A shooting buddy has a Winchester M54 in 22 Hornet. He can shoot cast almost as fast and accurately as his jacketed loads. Well, to about 2500 fps anyway . Heck, he even shoots pulled 40 gr 22RF bullets. These over light charges for fun and the occasional crow in his back yard.

I've shot cast 56gr boolits form my Savage M112 single shot .223 accurately to 2200 fps. It has a 12" twist. Actually the accuracy is still useable at 2400 fps but it isn't going to win any matches..................Buckshot"

A lot of casters, experienced and inexperienced, say something like "wow, he is shooting cast bullets accurately a lot fast than I am in my '06 and 6.5 Swede. Wonder why I can't do that." They can tweek the alloy, lube, sizing or case neck thickness all they want but the still won't get there ("there" being accuracy with cast as good as with jacketed at "speed"). The reason why, if we bother to look closely, is that a M52 in .22H has a 16" twist. That 2500 fps load is only cranking 112,528 RPM, close to the bottem of the RPM threshold. The Savage with the 12" twist at 2200 fps is cranking 132,000 RPM, up into the RPM threshold. They go over that and accuracy is lost. The .22H, in my experience since '75 with the Hornet and cast bullets, is that he is maxed out case capacity wise with a slow powder. Switching to a faster powder won't help but maybe an alloy change will alow another 100 fps or so. With the 12" .223 a change to a slower powder, an alloy change or different sizing might also get him another 150 fps before accuracy falls off but that's questionable as he already is well up into the RPM threshold.

Those are good example of how we see someone getting higher velocity with accuracy than we do and we think we should be able to do that also. You can IF you have the same twist. However, if your rifles barrel twist is faster you won't. It's all about RPMs when we want to go fast with accuracy using cast bullets.

Larry Gibson

felix
11-28-2007, 02:11 PM
More ammo for this discussion: The BR games during the 80's in the Houston Warehouse concluded without doubt the 22's are more accurate than the 24's by at least 1/3. Problem is nobody can realize that accuracy within realistic ambients. Folks who could shoot that good never chanced it, and I would not either considering the costs of attending the matches. There is a big difference between 22's and 24's, 50 grains versus 70 grains, where each is twisted at the preferred 14. ... felix

cbrick
11-28-2007, 08:11 PM
Fascinating thread and quite a can of worms. Here's some more food for thought.

Has anyone given thought to it being normally easier to get better accuracy at higher velocities with smaller diameter bullets (say the Hornet and 223 discussed in this thead aside from the well discussed twist rates? The "theory" being that any possible defect in a smaller bullet, be it from casting, sizing, loading or firing (internal ballistics), is closer to the center of axis during free flight (external ballistics) than it could be in a larger diameter bullet. This coupled with the bullet being lighter in weight it also has less mass spinning off center regarless of RPM's. Sectional denisty was the "key" referenced in the previously mentioned Handloader article.

Rick

leftiye
11-28-2007, 09:36 PM
Any given size and shape defect is also proportionately bigger in a smaller boolit. This means that the smaller boolit must be more perfect- have smaller defects- to be as precise, relatively as a larger boolit. Granted it is closer to the axis, and recieves less centrifugal force. Another factor favoring smaller bores is the lower sectional densities of their boolits (barring extreme designs). They will tolerate both faster accelerations (higher pressures) with a given alloy, and more RPMS (as you state).

felix
11-28-2007, 10:00 PM
Must weigh each 22 boolit to get high speed accuracy, dividing them into 1 tenth grain offset piles. The lower weight piles must be remelted. Take only three piles. If those three piles do not amount to 90 percent or thereabouts of all the boolits from that pot run, strongly consider another pot run. Segregate multiple pot runs using the same lead or not. A pot run is defined by each cold start. ... felix

scrapcan
11-28-2007, 11:02 PM
I will add something not mentioned and may not be of any value to this discussion, but here goes anyway.

In Robert Rinker's Understanding Firearm Ballistics there is a discussion about the Greenhill formula and the constant that is used. It is on pages 141-142. They make an adjustment for density of bullet material and also for velocities greater than 1800 fps (stated in the text as a change form 150 to 180 to account for a 20% slower twist and a 20% longer bullet).

anyway I don't know if this adds anything to this discussion or not. I had wanted to post this in another thread that discussed this topic, but did not.

joeb33050
11-29-2007, 08:24 AM
There's a lot of "why it does or doesn't exist" here, but little that I can see about demonstrating that it, the "RPM Threshold", does exist.
CBA records certainly include high RPM cases, although the average is lower.
I'll get some more CBA records put together.
Could the threshold merely be a combination of accepted twist rates and accurate velocities?
If the support is history, "The good shooters don't (often) exceed XXXXXX RPM.", could that be because of 12 twist 30 caliber barrels and the ~2000/2200 fps accurate velocity ceiling?

There's some reason that the SS breech seating guys shoot as well as or better than the fixed bolt guys in CBA competition. I don't know what that reason is, but have always imagined that bullet jumping forward AND having to start spinning, all in an instant.
Something makes it necessary to use harder bullets at higher velocities; could it be the damage at the initial jump on softer bullets?

Maybe the secret of CB accuracy lies in the gain twist barrel, from zero twist at the chamber end to minimum required twist at the muzzle.

Where can I read about the alluded to government testing?

Thanks;
joe b.

Bass Ackward
11-29-2007, 09:13 AM
Bass

Whens the last time you EVER saw a bench rest rifle with fore end pressure on the barrel, even cast bullet bench rest rifles? If what you say is correct then all of them ould have pressure on the barrel instead of none of them. Larry Gibson


Larry,

Time for another deep breath. Bear with me. Every time you have to stop and think about what I wrote, think about why you NEVER see a free floated military barrel.

You said yourself, jacketed accuracy can be found at low, medium or high velocity. Jacketed throws enough friction that as the speed increases, the vibration speed increases and the barrel whip is minimized. No bedding is needed because you simply alter your powder charge or your powder speed to get the vibration pattern needed for consistent shot to shot exits.

The wine glass with your finger routine. Slow and easy and the pitch is low and soft. Push harder and the pitch of the tone gets higher and louder. Ever play the geetar? A real lose string can be seen vibrating and drawn tight never seems to move.

With lead, you must stay with the slowest powder producing your best velocity or accept a lower velocity (RPM). So jacketed accuracy is a different bedding game. Stop here. You have to believe this or your wasting your time reading on.

Lead bedding logic SHOULD be different. It doesn't "have to be" if you can get best accuracy within the harmonics range you want to operate in with the barrel you have. (HV 30 caliber seems to be 2200 to 2400 fps) Bedding won't help then if you are accurate and it could make things worse. But lead, you can only throw so much friction before your lube breaks down and you lead. SO if your best (most accurate) load effort CAN"T reach the proper harmonics, then you MUST change the oscillating frequency which may be more pressure or more pressure farther out. Bedding does this. The farther out vibration is controlled, the less pressure is needed. But if you don't tune your lead, you live with the result.

(It's the same with jacketed and thus the 115 grin Speer reference in the 8.66 twist. While people believe it's the twist rate overstabilizing, it's the increased barrel FREQUENCY from speed (the finger on the wine glass again) making bullet harmonics and bullet exit at a single point (accuracy) even MORE difficult. We prooved in several rifles that light bullets COULD BE shot MORE accurately than heavy for which the 8.66 twist was designed. All we did was change bedding.)

Now, when a lead bullet reaches the point that lube breaks down and it .... grabs, that barrel and the vibration pattern is changed dramatically. (You pushed your finger harder on the wine glass and got a louder sound) So you get a flier. If you bed so that that change is trivialized, then you get less of a flier. Or so that is my logic. Same thing for minimizing humidy effect on lube and temperature, and metal fouling too. This is why militaries grab their barrel and hold it so as fouling alters accuracy, the effect is trivialized. A benchrester simply cleans his gun. Bedding does externally what a powder or charge change does. It's as simple as that. Maybe not as well, but well enough for lead.

Works as long as you aren't destroying bullet because of fouling, then all bets are off. You have to understand once you reached that point. Based upon my 35 Whelen tests last month with 4-6 BHN harder bullets and how that affect accuracy, I am going to get a .308 sizer and harden my bullets a tad and see if I can't shoot HV this winter.

When you slow the twist rate, you are in effect cutting pressure that alters the vibration pattern to allow higher velocity (RPM)s before the lead becomes unstable changing vibration again. Why not bed?

One more point: Larry "So what's that prove? Nothing much except your bullet shoots much more accurately down in the RPM threshold. That is just what I have been saying."

No all that prooves is that your gun shoots that bullet more accurately at that velocity. Free floated aren't ya?

Bass Ackward
11-29-2007, 09:43 AM
To those who feel this is an argument, I am sorry. It certainly is NOT on my part.

And while I am speaking to Larry, I will get to SHOW him later on when he comes out. I am really speaking AT everyone else. Minor subjects here never address a cast bullet gun. Only the bullet and load.

But I believe a cast bullet rifle is a different horse from what makes a good jacketed rifle and I have stated bits and pieces of this over the years, and Larry is the first to call me on it, forcing me to elaborate.

There are cases where we get a rifle that just does well with cast cause the conditions are just right. When they are not, we live with the RPM chart.

Sorry if I ofend anyone with my lecturing which is really just trying to express myself in as little space as possible.

andrew375
11-29-2007, 10:42 AM
Thanks, Andy. The more people speak up the better the statistics for those that have the BS flag in hand.

What powder? 4831?

VV N120, Blue Dot, and N135 so far.

andrew375
11-29-2007, 11:23 AM
Kindly show us pictures of the groups (if available) and load data so we may codgitate on it. Thank you.

Larry Gibson

Well [url=http://castboolits.gunloads.com/showthread.php?t=11228here's one [/url]I posted recently. Alright the bullet is only doing 168,000 rpm, but I've had the same performance at around 2400fps but with "slower" powders, principally Blue Dot and N120. The reason why this target is with N320 was that it is what I was loading at the time. I don't use the faster loads due to the increase in barrel heat and expense. If you choose not to believe any statement I make regarding my experiences then you may do so, though why I would make up the above statement is beyond me.

The reason why I responded to statement about maximum rpm limits is because the reasoning seemed a bit sparse. There could be any number of reasons why accuracy suffers at higher velocities, the main one has been shown to be failure of the bullet material to withstand the pressure. Dave Scovill wrote an excellent piece on matching bullet alloy strength to pressure in HandLoader. I've been shooting cast bullets for nearly thirty years and I have encountered all sorts of folk lore about cast bullets and what you cannot do with them. For example: .22 bullets are virtually impossible to cast, cast bullets are no good in a .223 because I'll be cleaning the lead out after each shot, they wont shoot in a fast twist as they will be ripped apart, etc. All of which I (we) know are false but I get lectured on by "experts" quite regularly.

BTW, I do not do extensive group shooting, just enough to determine that the load is worth bothering with, so I don't have an extensive archive of targets. I am principally a belly shooter: no rest, just a single point sling and glove. Very few of our ranges are fitted out for proper bench rest shooting and whilst I have a proper front rest and set of bags the stock on my savage, a McMillan Anschutz Prone, definitely is not a "bag rider". So unlike if were into bench rest I am not particularly "anal" about group sizes. Maybe I should be, who knows?:twisted:

As I said in the posting referred to above the rifle shoots groups like this just to keep me in my place, any poor quality shooting is purely down to the nut behind the trigger.

felix
11-29-2007, 11:44 AM
Andrew, find some N105 and use as BlueDot exactly by weight. Wider temp range accuracy, cleaner, and the same accuracy on a day well suited to BlueDot. ... felix

felix
11-29-2007, 12:10 PM
Joe, typically, gain twist will work against a boolit with quick acceleration. Would require deeper barrel grooves, keeping everything else the same. Shorter the boolit, the better the boolit will withstand the non-linear increasing rotational rate. Breach seating wins hands down, provided the breach seating technique keeps the boolits entirely concentric throughout the ignition phase. ... felix

Char-Gar
11-29-2007, 12:12 PM
Well, I certainly don't have any firm knowledge on this area, but that doesn't prevent me from adding my contribution to the fire plug.

Is it pressure or RPM.. that cause things to go South? Well, without pressure there are no RPM. More pressure produces more RPMs. So which is it?

I have a gut feeling that both play a part when juice on the bullet passes the point the alloy can withstand. The pressure pushes on the base, and the RMP rip at the sides of the bullet. They act together to kill the accuracy potential of that once wonderful cast bullet.

That are so many variables that I doubt if a fellow could codify the ceiling for RPMs or Pressure. Different cartridges, barrels, powders, and alloys will roll snake eyes at different points.

Junior1942
11-29-2007, 12:56 PM
I'd like to see some slow motion photos of a cast bullet going 150,000 rpms about 25 yards from the muzzle. I bet we'd see why my target holes had commas.

felix
11-29-2007, 01:07 PM
Charger, that is why multivariate analysis (cluster analysis, ect.) was invented. You can't codify these parameters without the proper equipment, and even if you did have the equipment, the time it would take to get a mess of data for the "cloud" would drive a person without the necessary incentive(s) absolutely nuts. ... felix

Larry Gibson
11-29-2007, 02:22 PM
I have a gut feeling that both play a part when juice on the bullet passes the point the alloy can withstand. The pressure pushes on the base, and the RMP rip at the sides of the bullet. They act together to kill the accuracy potential of that once wonderful cast bullet.

That are so many variables that I doubt if a fellow could codify the ceiling for RPMs or Pressure. Different cartridges, barrels, powders, and alloys will roll snake eyes at different points.

Pressure and RPM do go hand in hand but the effects are different. Take pressure; Load a '06 with 311291 to a pressure where obturation is excessive with and then load to the same pressure with 4898. The pressure is the same but the time pressure curve (acceleration) is slower with 4895. That means the 4895 load is not causing the excessive obturation yet and can be driven to a higher velocity before it does. Thus accuracy deterioration will happen at a lower RPM with 2400 than with 4895. This is why Bass talks of using the slow burning powders and he is correct. With the slow burning powders you can push a given bullet faster and maintain accuracy. So while pressure and RPM are related there is a difference in how one gets to pressure. Get there too fast and RPM will be low. Take your time getting to pressure and RPM can be higher.

Larry Gibson

Larry Gibson
11-29-2007, 03:45 PM
Et all; As Bass said this is not an arguement though it may seem that way to some. We are having a serious discussion here. As Bass said, we are bringing out lots of things we have learned and observed over the many years both of us have been casting bullets and shooting them.


Larry,

Time for another deep breath. Bear with me. Every time you have to stop and think about what I wrote, think about why you NEVER see a free floated military barrel.

Took the deep breath and have been thinking about it all morning. Yes I do know why we never see a free floated military barrel (except with todays application for SDM and sniper rifles). Bass, free floating barrels wasn't discovered (and accepted) to be a real aid to accuracy until the late '50s after the bench rest crowd proved over and over again that free floated barrels are more accurate. All of the surplus military rifles we have and shoot were made well before that discovery. Also all of the factory rifles were made with barrel pressure as that was the accepted way then. Those rifles were bedded with the techology that was known when they were made. That's WHY we don't see any free floated barrels military barrels.

You said yourself, jacketed accuracy can be found at low, medium or high velocity. Jacketed throws enough friction that as the speed increases, the vibration speed increases and the barrel whip is minimized. No bedding is needed because you simply alter your powder charge or your powder speed to get the vibration pattern needed for consistent shot to shot exits.

The wine glass with your finger routine. Slow and easy and the pitch is low and soft. Push harder and the pitch of the tone gets higher and louder. Ever play the geetar? A real lose string can be seen vibrating and drawn tight never seems to move.

With lead, you must stay with the slowest powder producing your best velocity or accept a lower velocity (RPM).

No problem with all of that, we're on the same page of the hymn book there.

So jacketed accuracy is a different bedding game. Stop here. You have to believe this or your wasting your time reading on. Lead bedding logic SHOULD be different. It doesn't "have to be" if you can get best accuracy within the harmonics range you want to operate in with the barrel you have. (HV 30 caliber seems to be 2200 to 2400 fps) Bedding won't help then if you are accurate and it could make things worse. But lead, you can only throw so much friction before your lube breaks down and you lead. SO if your best (most accurate) load effort CAN"T reach the proper harmonics, then you MUST change the oscillating frequency which may be more pressure or more pressure farther out. Bedding does this. The farther out vibration is controlled, the less pressure is needed. But if you don't tune your lead, you live with the result.

Guess I'm wasting my time but that's alright. You see all my rifles are not free floated. I have numerous military rifles that are still bedded as made. I do mostly bed all my sporters, varmint and target rifles. I've numerous times tried adding pressure to barrels to enhance accuracy. Only in a few instances over the years has it worked. That was most often with very thin barrels and the long (29 1/2") Mauser barrels when those were in sporter stocks. With barrels of normal contours they ALWAYS are most accurate with jacketed and cast bullets.

Now I'll give you a case in point. Years back I aquired a new 2 groove '03 barrel with 10" twist. Now everyone and their brother swore that 2 groove barrels are more accurate with cast bullets (they aren't by the way) so I thought I had the cat's meow for a cast bullet rifle barrel. I also had a M1916 (Oviedo made in '28) Spanish M93 action that had just shot out it's 3rd .308 Winchester barrel. I had converted it to cock on opening so the lock time was very quick. It had been a very accurate rifle with all 3 previous barrels shooting both J and cast bullets. I had dreamed up my .308 CBC then which is a shortened .308 case with an '06 length neck. case capacity was computed to be just enough 4895 to get a 311284 to 2200 fps. I had the 2 groove barrel set back, threaded for the SR mauser and short chambered with a tight necked .308 reamer and then a '06 reamer was used to lentgthen the neck. Conversion came out quite nice. Case were formed from unfired U.S. 7.62 cases with the necks turned for .002 clearence with a .311 bullet. However I quickly found that accuracy was best (1- 1/1/2 moa) with 311284 in the 1750 to 1850 fps range which is right smack dab in the RPM threshold. I was not yet aware of the RPM threshold as i didn't read about it until some time later. When I increased velocity, thus increasing RPM, accuracy deteriorated to 3-5 moa, That's exacty what that bullet (or 311041 or 311291) did in my 30-06 and one .308 which also had a 10" twist. To the point here; I have tried every concievable thing, including all manner of pressure to the barrel and nothing changes the accuracy. Yes , I also went to slower powders but the smaller case capacity didn't help. Point is, pressure to the barrel changed nothing as far as accuracy at any velocity when using cast bullets. I have also tried barrel pressure numerous times over the years on many different rifles. This was even recently with the RCBS 30-150-FN after I shot your 154 LBT bullets. Pressure of 2, 6 and 10 lbs did not change the accuracy one iota with those cast bullets at velocities from 1800 up through 2500 fps. Accuracy was still the best (1 1/2 moa consistantly with 10 shot groups) down in the RPM threshold and went to 5-6 moa (with 5 shot groups) at the high end.

(It's the same with jacketed and thus the 115 grin Speer reference in the 8.66 twist. While people believe it's the twist rate overstabilizing, it's the increased barrel FREQUENCY from speed (the finger on the wine glass again) making bullet harmonics and bullet exit at a single point (accuracy) even MORE difficult. We prooved in several rifles that light bullets COULD BE shot MORE accurately than heavy for which the 8.66 twist was designed. All we did was change bedding.)

I get quite good accuracy with that Speer bullet out of my M95 Mauser. I also know of several other 7mms that shoot that bullet well. Would appear more to me that you have a barrel there with a lot of internal stress. What most call a bad barrel. We still agree that pressure was helpfull there.

Now, when a lead bullet reaches the point that lube breaks down and it .... grabs, that barrel and the vibration pattern is changed dramatically. (You pushed your finger harder on the wine glass and got a louder sound) So you get a flier. If you bed so that that change is trivialized, then you get less of a flier. Or so that is my logic. Same thing for minimizing humidy effect on lube and temperature, and metal fouling too. This is why militaries grab their barrel and hold it so as fouling alters accuracy, the effect is trivialized. A benchrester simply cleans his gun. Bedding does externally what a powder or charge change does. It's as simple as that. Maybe not as well, but well enough for lead.

I pretty much agree with here but I'me not sure how you think the defects caused to the bullets aren't affected by the rotaional spin of the centrifical force of the RPM when the bullet leaves the barrel. That is what we're talking about here. That is where accuracy is primarily lost; the defects in the bullets (from what ever reason) are accentuated by the increased rotational speed at higher velocity and accuracy is not as good as it is at lower RPM. If a lube breaks down and the barrel is leading I don't really care what direction the barrel whip throws the bullet it is not going to be accurate. Have you ever had a leaded barrel shoot accurately? I haven't.

Works as long as you aren't destroying bullet because of fouling, then all bets are off. You have to understand once you reached that point. Based upon my 35 Whelen tests last month with 4-6 BHN harder bullets and how that affect accuracy, I am going to get a .308 sizer and harden my bullets a tad and see if I can't shoot HV this winter.

I think you're forgetting the adverse effect of obturation at high accelleration. Even if the lube doesn't break down and the fouling is minimal adverse obturation if cause by higher acceleration will cause imbalances in the bullet and accuracy will be adversely affected by the higher RPM. I will be most interested in the results of your tests. I too will test this winter. I will run identical loads through 3 very accurate .308 rifles; a 10" twist M788, A 12" twist M70 Target and the 14" twist M98 Palma rifle. I will keep you posted.

When you slow the twist rate, you are in effect cutting pressure that alters the vibration pattern to allow higher velocity (RPM)s before the lead becomes unstable changing vibration again. Why not bed?

I've seen numerous tests that show the pressure between a 10" and 12" twist barrel is essentially the same. Any measured difference fell between the shot to shot variation of pressure. Not sure how this is with a 14" twist though. I am probably going to put my money where my mouth is and get a piezo (SP?) pressure measuring system for Christmas. Hopefully I'll have an answer by next Summer.

One more point: Larry "So what's that prove? Nothing much except your bullet shoots much more accurately down in the RPM threshold. That is just what I have been saying."

No all that prooves is that your gun shoots that bullet more accurately at that velocity. Free floated aren't ya?

No Bass, they are not all free floated as previously stated. With or without free floated barrels the best accuracy with each, when using cast bullets, comes within or under the RPM threshold.


To be continued folks....

Larry Gibson

Larry Gibson
11-29-2007, 03:48 PM
joeb33050

Not ignoring you, just haven't had time to check the threads. Thanks for the reply and I do not doubt your veracity. I'm just always intersted in learning. I'll get back with a reply.

Larry Gibson

Bret4207
11-29-2007, 04:05 PM
So do you guys think a boolit (cast alloy) can actually be spun fast enough to cause the alloy to "fly apart"? Is it even possible for an alloy to resond like that or would it just become radically unstable and turn into a tumbling rock? Is the "vaporizing bullet" , either cast or jacketed, another old wives tale?

joeb33050
11-29-2007, 05:38 PM
So do you guys think a boolit (cast alloy) can actually be spun fast enough to cause the alloy to "fly apart"? Is it even possible for an alloy to resond like that or would it just become radically unstable and turn into a tumbling rock? Is the "vaporizing bullet" , either cast or jacketed, another old wives tale?

This is a topic that JA is working on. I asked another engineer here to handle it, but evidently I offended him-called him a name-in the past. This is easy, since:
There's no such thing as centrifugal force.
There is centripetal force.
We know the tensile strength of lead and alloys.

I suspect and forecast that no lead / alloy bullet will ever come apart because of the rotation.
I suspect that bullets blow up because the jacket or side is displaced or cut, amking the bullet wildly unstable.

Any competent engineer should be able to answer this question in a short time.
joe b.

joeb33050
11-29-2007, 05:42 PM
Here's a summary of RPM for CBA 2006, 2007 NM, with unknown and SS Breech seaters out.
Attached is the workbook. No it's not, this BD thing (B stands for BROKE) won't accept .xls files.

2006 CBA NM
RPM
Average 125,578
>150,000 1
140,000-150,000 6
130,000-140,000 3
120,000-130,000 10
110,000-120,000 9
100,000-110,000 4
<100,000 1

2007 CBA NM
RPM
Average 132,246
>150,000 2
140,000-150,000 6
130,000-140,000 12
120,000-130,000 6
110,000-120,000 7
100,000-110,000 9
<100,000 2

BD
11-29-2007, 05:48 PM
Although I've been keeping quiet, this thread has held my interest. It's my personal belief that there are more variables than we are willing/able to control simultaneously in this endevor. Thus the never ending discussion and room for "voodoo" in the process. To get real empirical evidence would require about ten identical rifles, each of which was bedded, rebedded and/or re-barreled simultaneously throughout the process.

I'm speaking up at this point to say that the "gray dust" phenomenon is possible, and I have witnessed it. I watched a dozen 40 grain .224 varmint bullets disappear with the evening sun at our backs out of a 9 twist .220 swift. These were loads that pushed a little better than 4,000 fps out of a 14 twist barrel. The 9 twist was built by a friend for sending the heavier bullets to coyotes across the frozen, windy lake. The 40 grainers were left from the previous 14 twist barrel and shot specifically to see if they'd go to pieces. They did. You could see the dust streaks as well as the fragments, (jacket bits?), kicking up dust downrange.

BD

BD
11-29-2007, 06:00 PM
I'm not claiming that I know what specific factor(s) causes the gray dust, only that I have seen the effect.

I'm of the opinion that sectional density may play a role as well. This is based on the single observation that if I push the 140 grain 6.5 Jumptrap's to 2,000 fps in a 7.8 twist Swede the groups open up to 14" or 16". If I push the cruise missle to the same velocity in the same Swede the groups open up to 6' or 8'.

BD

Char-Gar
11-29-2007, 06:01 PM
Felix.... I am certainly glad the tech folks came up with a term/process to deal with the crap we simple minded folks find stupifying.

Larry... Yea... I sorta figured the given the same peak pressure, a slow powder would allow more RPMs than a fast powder.

I think we have known for several lifetimes that with fast powders accuracy goes South at a lower velocity than with a slower powder. We always knew it was how fast the pressure was applied to the bullet that resulted in the accuracy differential. You boys are just trying to figure out why?

Blammer
11-29-2007, 06:12 PM
so, out of all of this....

I should take that a GOOD place to start with a .308 dia bullet of 225gr (311284) for a 30-06 with a barrel twist of 1-10 would be to try for 1800 fps to start for a good accurate hunting load?

Junior1942
11-29-2007, 06:23 PM
Although I've been keeping quiet, this thread has held my interest. It's my personal belief that there are more variables than we are willing/able to control simultaneously in this endevor. Thus the never ending discussion and room for "voodoo" in the process. To get real empirical evidence would require about ten identical rifles, each of which was bedded, rebedded and/or re-barreled simultaneously throughout the process.

I'm speaking up at this point to say that the "gray dust" phenomenon is possible, and I have witnessed it. I watched a dozen 40 grain .224 varmint bullets disappear with the evening sun at our backs out of a 9 twist .220 swift. These were loads that pushed a little better than 4,000 fps out of a 14 twist barrel. The 9 twist was built by a friend for sending the heavier bullets to coyotes across the frozen, windy lake. The 40 grainers were left from the previous 14 twist barrel and shot specifically to see if they'd go to pieces. They did. You could see the dust streaks as well as the fragments, (jacket bits?), kicking up dust downrange.

BDThat's 320,000 rpms.

Larry Gibson
11-29-2007, 07:49 PM
Andrew375

That is a nice group, especially for a belly shoot. The velocity is chronographed? As you say in that thread that one group does not accuracy make so does it do that well consistantly? You obviously have a nice load there at any rate.

Larry Gibson

waksupi
11-29-2007, 09:05 PM
Guys, I'm not the brightest bulb on the Christmas tree, when it comes to math.

Is

(velocityX60) divided by (Twist divided by 12) = RPM the correct formula?

Nueces
11-29-2007, 09:16 PM
Yup, that's it, or, the same thing; 720 (which is your 60 times 12) times velocity divided by twist.

Mark

KYCaster
11-30-2007, 12:07 AM
Velocity in ft/sec X 60 = velocity in ft/min X 12 = velocity in in/min, divided by twist = RPM.

Jerry

andrew375
11-30-2007, 05:21 AM
Andrew375

That is a nice group, especially for a belly shoot. The velocity is chronographed? As you say in that thread that one group does not accuracy make so does it do that well consistantly? You obviously have a nice load there at any rate.

Larry Gibson

All my loads are chronographed. I don't make any claims as to consistency as there are too many variables muddying the water introduced by the shooter. The rifle may be consistent but I'm not! I am getting better though.

joeb33050
11-30-2007, 08:23 AM
Again, if the RPM threshold is based on what folks are shooting, then I think we're making a mistake.
The Production class revolves around a Savage .308 with a 10" twist and a bullet going 1800-2100 fps. This isn't because folks choose the gun or the twist or the cartridge, it's because that's what's out there and available.
If we had our choice, the Savage might be in 30BR or 7.62 X?? or 30/30-smaller cartridge case; and the twist might be 12 or bigger #.
One 2007 competitor used a 18" twist barrel in 30BR at 2750 fps with a 108 grain monotype bullet.
The CBA experimenters/rifle builders seem to be going toward the 30BR Score jacketed direction without-maybe-thinking this through.
The SS breech seaters are shooting almost as well at much lower velocities with heavier bullets. Why aren't the experimenters going toward long heavy bullets in gain twist barrels at 1400 fps?
joe b.

felix
11-30-2007, 10:15 AM
Reason: because the longer the boolit is, the more distortion it receives in a gain twist barrel. If the barrel is going to be made with cut grooves, then a very, very small amount of gain twist might help the cutter mechanism do a more consistent cut job. ... felix

JudgeBAC
11-30-2007, 10:45 AM
This may be off topic and, if so, I apologize. Is the following observation a factor of velocity, RPM, a combination of the two, or some other factor? My model 29-10 6.5" bbl with a 255 gr. Keith bullet over 9 gr. of Unique places these 1" above the sights at 25 yards and to a similar place at 50 yards. A 277 gr. MM bullet over 9 gr of Unique places the bullets 3.5 to 4" LEFT of the sights at the same distances. What gives?

felix
11-30-2007, 10:56 AM
Position of impact at 25 yards with a revolter has more to do with how the gun recoils more than anything. The left-right business at that distance might have something to do with how the boolit style makes it through the forcing cone based upon mechanical conditions. I have found that the Unique speed of powder needs to be very close to being right on. If you vary the powder by half grain on either side of a proverbial sweet spot, and the accuracy goes out by a visual amount, then pick another powder. So, try to adjust the loads between each boolit. This is more of a question for the 44man and others who play hard ball with pistols. ... felix

JudgeBAC
11-30-2007, 11:11 AM
Felix, thanks for your thoughts. I moved this query to the wheelgun forum.

Larry Gibson
11-30-2007, 12:21 PM
All my loads are chronographed. I don't make any claims as to consistency as there are too many variables muddying the water introduced by the shooter. The rifle may be consistent but I'm not! I am getting better though.


Understand, I've shot quite a few "belly" matches myself.....some days are diamonds, some are stones!

Larry Gibson

joeb33050
11-30-2007, 12:25 PM
Reason: because the longer the boolit is, the more distortion it receives in a gain twist barrel. If the barrel is going to be made with cut grooves, then a very, very small amount of gain twist might help the cutter mechanism do a more consistent cut job. ... felix

I don't think so. The bullet is going to turn and get engraved no matter what.
Smith gain twist barrels are used by the SS guys with good results.
I think the CBA fixed experimenters are like all people, doing what's new and popular without stopping to think about it deeply.
Gain twist has worked for 150 years, although a good fixed twist barrel works fine too.
joe b.

felix
11-30-2007, 01:07 PM
There is a difference in knowing so and thinking so, Joe. However, on your behalf, there is safety in numbers. ... felix

Larry Gibson
11-30-2007, 05:08 PM
Woke up this morning and since the wife was sleeping in I turned on the Mag 20, put some 60/40 WW/Lino alloy in it, degreased two Lyman 2 cavity moulds (311291 and 311466), put a pot of coffee on, turned on some smooth jazz on the radio and commenced to cast 16 lbs worth of bullets.

My plan is to test identical loads for for three .308 rifles; a M788 with 10" twist, a M70 target with 12" twist and the M98 Palma with the 14" twist. The goal is to observe accuracy improvement or deterioration as velocity is increased from around 1700 fps up through 2500+ fps with each rifle. The reason for the test is to observe what the average guy may get accuracy wise with the .308 based on different twists. I chose the 311291 because it is readily available and a proven design. The 311466 was chosen because it is Lymans' fastest .308 Winchester bullet (2920 fps with 748) in their new Cast bullet Manual.

Bullet selection will be by visual inspection for defects with only the bullets with complete fillout and no wrinkles or voids being used. I do not intend to weight the bullets or sort them by cavity. Right now the 311291s are .309 - .310 so it looks like a .310 sizer will be used. The 311466 drops at .315!!!! Not sure whether I'll test them at .314 or size them to .311 (after lubing) for the test. Gas checks will be Hornady's and they'll be seated using the GC seater on the 450 then the 311291s will be run through a Lee .310 sizer then lubed in a Lyman .310 H die. The 311466's, after seating the GCs on the 450, will be run through a Lee .314 then lubed in a Lyman .314 H die in the 450. It may be shot as is or then run through a .311 Lee sizer.

Cases will be once fired (through the M70) LC 92. Necks will be inside reamed in a Lee Target Loader for unifromity and concentricity. Primers will be WLR and Remington 9 1/2s. Lube will be Javelina as I've not had any lube failure with it up through 2600+ fps.

Powders will be; 4895 with a Dacron filler used until loading density is 80%+, RL19 and H4831SC.

Testing will be done at Tacoma Rifle and revolver Club which has very sturdy cement benches. All loads will be over the Oehler 35P chronograph. Targets will be at 100 yards. The end result will be NOT to compare the accuracy of the rifles against each other (I already know which rifle will win that one). The test will be to observe accuracy of each rifle as it increases or decreases through increasing powder charges and how accuracy responds as velocity/RPM is increased. Testing identical loads in the 3 rifles with 3 different twists should then give us some indication on the effects of RPM.

Any other suggests? Remember this test is to replicate those cast bullet loads that the average cast bullet shooter would produce. As the average cast bullet shooter doesn't get too anal in reloading technique/detail neither shall I.

Larry Gibson

felix
11-30-2007, 05:35 PM
Good show, Larry! Should be a fun experiment. No hurry. ... felix

sundog
11-30-2007, 05:51 PM
Hooah, Larry. Over a chrono, but what are you gonna do? Groups for each load for each rifle?

My take is that your test will actually produce enough data to tell something. I'll reserve my SWAG until after your data is compiled (although I have my suspicions). Looks like you'll be getting some quality trigger time!

Blammer
11-30-2007, 06:32 PM
got any 311284 boolits? Them would be nice to test too.... lol as if you don't have enough covered.

Pat I.
11-30-2007, 08:17 PM
I think the CBA fixed experimenters are like all people, doing what's new and popular without stopping to think about it deeply.
Gain twist has worked for 150 years, although a good fixed twist barrel works fine too.
joe b.

Of course this is right. I spent 250 bucks on a 17 twist Shilen barrel, 150 on a reamer, 125 for a LBT mould plus the RCBS 22 cal mould blocks I used to make another bullet, brass, dies, powder, time putting it all together, and a bunch of other things and did it all on a whim with no thought involved. Since there was only my 17 twist and the other fellas 18 twist, which you failed to mention he used to win the unrestrcted class with, 30 caliber barrels on the line I don't think either of us chose it because it's new or popular. His is a 30 BR mine is a 30x47, lots of those being shot isn't there.

waksupi
11-30-2007, 10:07 PM
Harry Pope, and his contemporaries, never did really settle on wheter gain twist was better or not. I'm with them.

ssn vet
11-30-2007, 10:29 PM
this is really interesting......especially for newbs like me....

reminds me of the velocity limits published by the plated bullet mfg.s

Berrys normally states a limit of 1,200 fps on their pistol bullets and on the 150 gr .308 FN I load for my Marlin 336, they say 1,700 fps (numbers pulled from memory, it's been a while).

The best explanation I've heard for this is because the copper plating starts to "spin off".....but I wonder

These plated bullets have a pretty soft swaged cores, I wonder if that comes into play....

sorry for the thread hijak, I find the topic very intereting

felix
11-30-2007, 10:52 PM
No hijack... Yes, a heavy (and not too tightly woven) core will want to push off a jacket. Any hole found will let loose a bomb, re 220 swift, 22-250 types using the thinner jacket bullets. Maybe a depleted uranium core will take 2 times that rotational velocity before even thinking about getting nervous. ... felix

joeb33050
12-01-2007, 07:40 AM
Of course this is right. I spent 250 bucks on a 17 twist Shilen barrel, 150 on a reamer, 125 for a LBT mould plus the RCBS 22 cal mould blocks I used to make another bullet, brass, dies, powder, time putting it all together, and a bunch of other things and did it all on a whim with no thought involved. Since there was only my 17 twist and the other fellas 18 twist, which you failed to mention he used to win the unrestrcted class with, 30 caliber barrels on the line I don't think either of us chose it because it's new or popular. His is a 30 BR mine is a 30x47, lots of those being shot isn't there.

Pat;
You seem defensive. There's no need. Maybe it's a coincidence, but the trend to slow twist short bullet rifles in CBA seems-seems-to follow that trend in jacketed score shooting.
Comparison of results in CBA NM shooting has shown the PB breech seaters doing virtually as well as anyone else, when there are enough of them attending.
Perhaps the slow twist short bullet fast plan is the route to ultimate accuracy with CBs, but I wonder what could be done with long bullet appropriate twist slow bullets with ?gain? twist barrels.
You've got the "where we are now", then two diametrically opposed alternatives that present themselves. Movement seems to be toward one of those alternatives, with no movement toward the other.
Maybe, as I said, maybe, this is happening without the experimenters thinking this through all the way.
And maybe not.
Regardless of that, my impression is that the slow twist fast short bullet guys do not go to the slow twist because they percieve an RPM threshold ahead.
joe b.

joeb33050
12-01-2007, 07:44 AM
Harry Pope, and his contemporaries, never did really settle on wheter gain twist was better or not. I'm with them.

I certainly can't prove it, but the ASSRA scores/groups improvements in the past few years might just have something to do with those Smith (and other) gain twist barrels.
Something happened, so that we see multiple 250s shot in matches.
joe b.

felix
12-01-2007, 10:40 AM
Again, Joe, shorter the boolit (engraving section) , the better the gain twist works. Also, the tougher the boolit, the better it works. Gain twist requires that the boolit comes back to normal after changing from being twisted at different rates from front to back within the engraving section. .... felix

joeb33050
12-01-2007, 11:38 AM
Again, Joe, shorter the boolit (engraving section) , the better the gain twist works. Also, the tougher the boolit, the better it works. Gain twist requires that the boolit comes back to normal after changing from being twisted at different rates from front to back within the engraving section. .... felix

Shorter = works better. Any data?
Tougher = better. Any data? Bev Pinney, PBB winner, used 30:1, Smith gain twist. Duane Jenner used 25:1, Smith gain twist. These were the two gain twist guys at the 2007 CBA NM

I don't know what your last sentence means.
If the gain twist gains at all points along length, then the front of the bullet is being twisted faster than tha rear, but imperceptibly in any normal = 1" bullet length. There is always this, and always the angular delta per inch of barrel increases.
Starting with the bullet breech seated, the front of the bullet has been turned at some angle theta and the rear has been turned at theta-D for difference.
As the bullet moves down the barrel, twist increases, theta increases, and theta-D increases.
With a gain twist barrel, the first derivitive of theta or theta - D WRT L = barrel length, is a positive number. With a constant twist barrel the first derivitive is zero.
Pope wrote that the constantly changing angle kept the bore-bullet interface sealed. Or sealed better. This of course was before the invention of obturation.
I don't know if the gain twist helps accuracy, results are mixed.
I do think that in a good bolt gun, a breech seated bullet may shoot better, and it may shoot even better in a gain twist barrel.
And, the gun is available, unlike the DeHaas Miller actions that are as close to unobtainable as possible.
A stock Savage 308 with breech seated bullets is easy to try, and the twist is fast enough for long bullets. A breech seater can be ginned up by a competent machinist or hobbyist.
If that worked, changing the gun to switch-barrel and using a ?Smith gain twist barrel in 30BR or a cartridge similar to 32MS in volume and shape would allow a first-look estimate of the effect.
The Savage is approximately infinitely more available than any competitive SS rifle, and 1/4 to 1/6 the cost, and years faster to acquire.
At my age I have to consider the gunsmith velocity if I'm having a gun built. Answers to the analysis are not encouraging. I may get the gun before I croak, but will I know why I ordered it and what to do with it? Or my name?
Anyhow, why doesn't someone tell me where I can read about the Government testing having to do with RPM???
Larry? Anybody???
joe b.

Pat I.
12-01-2007, 02:49 PM
How do you know Bev or Duane are using gain twists? I don't and I know them both. Why don't you find a 6.5 Carcano to play with? If you decide instead to have a Smith GT barrel put on one of your guns, it doesn't have to be a Savage to see the results, keep me posted since I'll be wallowing around doing things without thinking them through.

Larry Gibson
12-01-2007, 07:13 PM
joeb33050

The tests were conducted by the U.S. Ordnance Technical Committee. They recommended the adaptation of the T65 cartridge (7.62 NATO) in a rifle with 1-12" twist. I'm not sure where to find their published report on it as it's been years since I read it. It is most often erroneously published that the T65 cartridge was to replace the M2 cartridge with it's attendant velocity of 2800 fps. That is not the case. First of all the Arsenals did not produce any M2 ammo that attained 2800 fps. That was the plan but the M1 cartridge superseded the plan to up the M1903 ammo velocity to 2800 fps (originally 2700 fps). Problem was the M1 ammo’s range exceeded the maximum the range fans of most military ranges allowed. M2 ammo came about when the arsenals were asked by the War Department to load some equivalent ammo to M1903 ammo for “practice” stateside as the WWI produced stocks of M1903 ammo had been exhausted. M2 Ammo was loaded to nominal 2650fps by the arsenals to meet this requirement. I’ve a copy of the memo directing such velocity BTW.

Back to the point; T65 ammo was designed and loaded to match the trajectory of M1 ammo (174 gr FMJBT at 2640 fps) out to 1200 yards (1100 meters). The 147 gr M80 or the M59 150.5 gr bullets were loaded to 2750 fps 78 ft from the muzzle. It was found a 12” twist gave the best accuracy at maximum range over a 10” twist. Note: many also think the max effective range of the M14 was/is 450 meters (500) yards but that also is not correct. The 450 max effective range is the max effective range using hold over with a battle sight zero (250 meters). Maximum effect range actually is 620 meters for the M14 and 1100 meters for the M60 GPMG. With the rear sight of the M14 properly zeroed it is quite possible to adjust the sight (that’s what the elevation scale is for on the elevation knob) and hit an E target 80% of the time at 700 yards (the 620 meters).

Palma Matches were originally shot with issue rifles and ammo provided by the host country. Palma Matches are belly matches fired at 800, 900 and 1,000 yards. Since 7.62 NATO was the ammo in use by the host nations the ball ammo of 145-155 gr was used. The rules changed that allowed the visiting nations to bring their own rifles, initially service rifles and then any rifle, in 7.62 NATO as the host nation continued to supply issue service ammo. The match shooters picked up on slower twists not accentuating the defects due to RPMs. Initially the match rifles had 12” twists but then they lengthened the barrels to 27 ½ - 32” to obtain maximum velocity. This increased RPM and accuracy with ball 7.62 ammo was adversely affected. It was quickly found that a twist of 13 or 14” dramatically improved the accuracy of 7.62 Ball. Some equivocate this with rounds that “go to sleep” but it actually is different. The adverse affects that RPM has on bullet imbalances is a proven fact.

Larry Gibson

Bass Ackward
12-01-2007, 09:13 PM
The adverse affects that RPM has on bullet imbalances is a proven fact. Larry Gibson


Twist rate is determined by the range that you want to fling a certain weight / length / ballistic coefficient object in a stabilized fashion. The more screwed up or less aerodynamic the projectile, (the wider the meplat) the more velocity you will need to start it out at. If your velocity ceiling is limited, then you will need to increase your twist rate to stabilize it farther out. (wadcutters) This is external ballistics and why nose shape / meplat size eats up twist rate. Or lowers RPM ceilings.

Internal cast ballistics dictates that a slug trying to accelerate is retarded by a twist rate angle in the bore. The more the rate angle is increased, (faster twist) the more that bullet will be held back and pressure will work on the base. In effect, it's the same as using a faster powder and we all know that slower powders do allow higher velocities. :grin: Also the more barrel time it will have exposed to that pressure. And the result will be the more barrel vibration and greater harmonics will take place. That is also why the lightest bullet per caliber achieves the highest RPM. And why softer bullets can be used with slower twist rates. And why larger case capacities lengthen pressure curves. Not because of stripping or bullet damage as most believe.

So, when you lose cast accuracy is it because of external ballistics or internal ballistics at short ranges? :grin: Actually both. You work to mold to achieve perfection and your twist rate fights to destroy it. Pressure does the damage.

Larry Gibson
12-01-2007, 09:51 PM
Bass

It would it appear that you agree with the statement of mine you quoted! I've no arguement with your discertation as it quantifies the quote.

Larry Gibson

sundog
12-01-2007, 10:40 PM
Gain twist is just that. BUT, you really need to know the start and end twist... 10 to 12? 13 to 14? AND what bore? .308ish, 32ish, ??? Otherwise it doesn't mean much. Gradual, abrupt?

Anyone know for sure the start/end for the Smith bbl?

I shot today in the big wind. S20-G40, light rain showers, and VERY overcast.

Chargar's Lee 311291 in the .303 over 18.0/surp4759 and dacron wad went less than half inch by 4 inch vertical for ten shots. GT line is 360 (wind directly at back). Thinking about bumping it a grain.

Also shot 03A3 scoped sporter with 25.0/4198 and dacron wad with Beagled SAECO 301 WQ, Beagled 311284 WQ, and 314299 HT. 311284 was purdy good, but as usual the 314299 was the best. It and the 311299/40.0/4895 WQ can hold the white of the old gieser target at a hunert for five shots. Worth the trip to the range.

sundog
12-01-2007, 10:41 PM
Oooo,, actually a gain twist would be something like 14 to 12, number has to reduce to speed up the spin....

Sorry 'bout that.

Pat I.
12-02-2007, 08:04 AM
I won't bet my life on it but I think you can choose the start and end twist with the Smith barrels, like 19 to 11 or 20 to 14. If I remember right the Carcano's was something like 19 to 8 and would be a cheap way for Joe to test it out.

joeb33050
12-02-2007, 08:28 AM
How do you know Bev or Duane are using gain twists? I don't and I know them both. Why don't you find a 6.5 Carcano to play with? If you decide instead to have a Smith GT barrel put on one of your guns, it doesn't have to be a Savage to see the results, keep me posted since I'll be wallowing around doing things without thinking them through.

"How do you know Bev or Duane are using gain twists? I don't and I know them both."

I consulted the Nov Dec 2007 Fouling Shot, looked in the NM equipment lists, and, as they say, voila!!

I think I'll try breech seating a bolt gun, I mentioned the gunsmith velocity which keeps me from trying to have a gun built. The famous Competitor SS pistol that was to be delivered in under 10 weeks is now 17 weeks underconstruction and no news.

joe b.

Pat I.
12-02-2007, 09:02 AM
[QUOTE=joeb33050;252629 I consulted the Nov Dec 2007 Fouling Shot, looked in the NM equipment lists, and, as they say, voila!! joe b.[/QUOTE]

Well ya got me there for sure! Guess it gives credence to the old saying that even a blind hog can find an acorn once in a while.

Bass Ackward
12-02-2007, 09:59 AM
Bass

It would it appear that you agree with the statement of mine you quoted! I've no arguement with your discertation as it quantifies the quote.

Larry Gibson


Larry,

Not always. Remember, the 115 grain Speer example. If something can be beaten just once, then it isn't a fact. A better term might be "inflexible trend". The real question is how flexible (anal) do you want to be?

What's the most accurate cartridge in the world? A 30 PPC at 100 yards? A 300 Win Mag at 1000? Or a 303 British at 1319 meters? (I think that distance is correct.) Can a palma rifle compete to win in any of these categories with generic bulk ammunition regardless of twist rate? Who expects to do well at a 1000 yard match with a 20" barrelled 30 PPC? Or someone at a bench rest competition with a military 303. So why can't we consider a cast as another possibility to make use of our desires instead of using only a set amount of variables to draw up .... "easy" limits?

So why when we come to lead, is the limit the lead because of a single variable? RPMs? Don't we match hardness to the pressure to defeat it? And if going up in hardness by just 6 BHN requires .001 down sizing in bullet diameter for me to get the same groups, can I not be anal (sometimes you don't have too as some guys can find HV almost by accident.) to try something else instead of just blaming it on RPMs?

In other words, if just one guy can, ask why can't " I "? The answers are advancing. If you accept an RPM level as "your" guide, you trivialize the shooting and reloading process to blame your or your guns failure. Simple as that. So all of this jumps around the hot button issues. We don't define accuracy standards. We don't define poor or defective cast guns. And we don't define anal. And without that, we can't develop an RPM ceiling without including .... defective and limiting data. (statistics)

So your test to find best "average accuracy" with what's "reasonably" available off the shelf or steps that are taken is fairly useless. If you want to prove "easiest accuracy" that a slower twist is more .... "idiot proof" and minimizes errors as a reloader and shooter of cast, save your components, I'll give you that. Cast or jacketed as your palma post shows.

Question that should be asked, are you interested in generic accuracy or specialized and specific accuracy? One requires more than the other. But just because you choose to run your two mile PT test with a 35# ruck on your back filled with beer for the trip, don't blame me when your times don't meet the standard. And that's what your test is really talking here. I want this without having to do or meet that. Fortunately, cast accommodates everyone and the HV guys are changing the stereotype. :grin:

joeb33050
12-02-2007, 01:34 PM
joeb33050

The tests were conducted by the U.S. Ordnance Technical Committee. They recommended the adaptation of the T65 cartridge (7.62 NATO) in a rifle with 1-12" twist. I'm not sure where to find their published report on it as it's been years since I read it. It is most often erroneously published that the T65 cartridge was to replace the M2 cartridge with it's attendant velocity of 2800 fps. That is not the case. First of all the Arsenals did not produce any M2 ammo that attained 2800 fps. That was the plan but the M1 cartridge superseded the plan to up the M1903 ammo velocity to 2800 fps (originally 2700 fps). Problem was the M1 ammo’s range exceeded the maximum the range fans of most military ranges allowed. M2 ammo came about when the arsenals were asked by the War Department to load some equivalent ammo to M1903 ammo for “practice” stateside as the WWI produced stocks of M1903 ammo had been exhausted. M2 Ammo was loaded to nominal 2650fps by the arsenals to meet this requirement. I’ve a copy of the memo directing such velocity BTW.

Back to the point; T65 ammo was designed and loaded to match the trajectory of M1 ammo (174 gr FMJBT at 2640 fps) out to 1200 yards (1100 meters). The 147 gr M80 or the M59 150.5 gr bullets were loaded to 2750 fps 78 ft from the muzzle. It was found a 12” twist gave the best accuracy at maximum range over a 10” twist. Note: many also think the max effective range of the M14 was/is 450 meters (500) yards but that also is not correct. The 450 max effective range is the max effective range using hold over with a battle sight zero (250 meters). Maximum effect range actually is 620 meters for the M14 and 1100 meters for the M60 GPMG. With the rear sight of the M14 properly zeroed it is quite possible to adjust the sight (that’s what the elevation scale is for on the elevation knob) and hit an E target 80% of the time at 700 yards (the 620 meters).

Palma Matches were originally shot with issue rifles and ammo provided by the host country. Palma Matches are belly matches fired at 800, 900 and 1,000 yards. Since 7.62 NATO was the ammo in use by the host nations the ball ammo of 145-155 gr was used. The rules changed that allowed the visiting nations to bring their own rifles, initially service rifles and then any rifle, in 7.62 NATO as the host nation continued to supply issue service ammo. The match shooters picked up on slower twists not accentuating the defects due to RPMs. Initially the match rifles had 12” twists but then they lengthened the barrels to 27 ½ - 32” to obtain maximum velocity. This increased RPM and accuracy with ball 7.62 ammo was adversely affected. It was quickly found that a twist of 13 or 14” dramatically improved the accuracy of 7.62 Ball. Some equivocate this with rounds that “go to sleep” but it actually is different. The adverse affects that RPM has on bullet imbalances is a proven fact.

Larry Gibson

This is hard for me to understand. Is this what happened?
"The 147 gr M80 or the M59 150.5 gr bullets were loaded to 2750 fps 78 ft from the muzzle. It was found a 12” twist gave the best accuracy at maximum range over a 10” twist. "
This having to do with the M14 rifle with ??24"?? barrel. Yes? No?

Then
"Initially the match rifles had 12” twists but then they lengthened the barrels to 27 ½ - 32” to obtain maximum velocity. "
"accuracy with ball 7.62 ammo was adversely affected. It was quickly found that a twist of 13 or 14” dramatically improved the accuracy of 7.62 Ball. "

So, at M14 velocity the 12" twist was shown to be more accurate than the 10" twist.
At greater velocities due to longer barrels accuracy decreased.
With the longer barrels slower twist brought the accuracy back.

2750 fps 10" twist = 198000 RPM
2750 fps 12" twist = 165000 rpm
correct to MV from 78", a guess:
2800 fps 10" twist = 201600
2800 fps 12" twist = 168000
correct to long barrel, a guess. 32-24 = 8 X 30fps = 240 fps+2800 fps = 3040 fps in palma guns
3040 fps 10" twist = 218880
3040 fps 12" twist = 182400
3040 fps 13" twist = 168369
3040 fps 14" twist = 156343

Am I understanding what happened? Not why, still working on what.
Thanks;
joe b.

felix
12-02-2007, 01:58 PM
Looks good to me, Joe! ... felix

Ricochet
12-02-2007, 03:23 PM
...think about why you NEVER see a free floated military barrel.
That overlooks the many Mosin-Nagants with free-floating barrels. The Finns in particular practiced that quite deliberately by shimming the actions on their rebuilds to float the barrels, and they were doing that way before the '50s. I have standing beside me as I type a 1943 Izhevsk M91/30 that free-floats when the action screws are properly adjusted. Shoots a whole lot better that way than when the front screw's overtightened and pulls the barrel down against the tip of the stock, too. Or when it's benchrested too far out on the skinny front part of the stock, pushing it up to touch the barrel.

Larry Gibson
12-02-2007, 05:03 PM
.......So, at M14 velocity the 12" twist was shown to be more accurate than the 10" twist.
At greater velocities due to longer barrels accuracy decreased.
With the longer barrels slower twist brought the accuracy back.

2750 fps 10" twist = 198000 RPM
2750 fps 12" twist = 165000 rpm
correct to MV from 78", a guess:
2800 fps 10" twist = 201600
2800 fps 12" twist = 168000
correct to long barrel, a guess. 32-24 = 8 X 30fps = 240 fps+2800 fps = 3040 fps in palma guns
3040 fps 10" twist = 218880
3040 fps 12" twist = 182400
3040 fps 13" twist = 168369
3040 fps 14" twist = 156343

Am I understanding what happened? Not why, still working on what.
Thanks;
joe b.


That is it exactly regarding how RPM is lowered to lesson the effects on accuracy caused by imbalanced bullets. I don't think anyone here thinks issue ball bullets are that well made to be considered "balanced".

The initial testing, for a new service rifle/cartridge, criteria was for a 22" barrel. That is what the M14 has on it.

Larry Gibson

felix
12-02-2007, 05:55 PM
Military bullets are about worthless for BR work. I have tried many different ones because they were/are cheap. I would say offhand they would be close to equal hurried-up cast boolits at best. Now we are talking 3250 (circa 55 grainers) versus 2400 (circa 60 grainers) respectively here, the appropriate speeds for each type in this particular bench gun. 14 twist: 170K versus 125K RPM respectively. So, you can get 50K more RPM with military boolits for the same accuracy (in this gun). ... felix

Larry Gibson
12-02-2007, 06:25 PM
Bass

The question here is rather straight forward;

Why is it the average reloader when he gets a regular mould from Lyman, RCBS, Lee or Saeco for his rifle can get accuracy at a certain velocity yet loses accuracy above that velocity?

With the 30-06 for expample he gets good accuracy in the 1700-1900 fps range but above that he gets poor accuracy. He casts the bullets of WWs or an alloy like #2 as mentioned in Lyman's or RCBS cast bullet manuals and uses normal loading techniques as per the manuals. I believe the reason is that above a certain threshold of RPM (the threshold is a range of velocity of 125-140,000 RPM not a specific "limit") accuracy deteriorates with such cast bullet loads as the increased RPM accentuates the inbalances in the bullet (caused during casting, by poor fit, excessive obturation during accelleration, etc.). The increased RPM causes the yaw, pitch and wobble to be increased and accuracy suffers as the higher the velocity the higher the RPM.

I'm attempting to answer that question; is that too hard to understand? I think it is not as you've already conceded that RPM does have an adverse effect on accuracy of cast bullets; " So your test to find best "average accuracy" with what's "reasonably" available off the shelf or steps that are taken is fairly useless. If you want to prove "easiest accuracy" that a slower twist is more .... "idiot proof" and minimizes errors as a reloader and shooter of cast, save your components, I'll give you that." BTW; the use of the slower twist is to keep the RPM under the threshold while attaining a higher velocity. Our example shooter is not going to get another barrel for his favorite '06, he wants it to shoot as is.

Now as to the rest of your last post; yes you can get around the RPM threshold by getting "anal". There are a number of things one CAN do, but the average cast bullet shooter isn't going to do them. He neither has the equipment, the knowledge nor the desire. He just wants to cast bullets, load them in the rifle that he has and go shoot them. He is not going to get a different rifle, new molds, a lot more casting equipment or make some exotic alloy. He just wants to know why his bullets won't shoot accurately above 1900 fps or so out of his '06. And by just casting and shooting regular bullets he is not going to get accuracy above the threshold, now is he. The reason he won't get accuracy above a certain velocity with his 10" twist '06 (or any other rifle of 12" twist or faster) is EXACTLY what we are talking about, isn't it?

The question isn't about getting anal is it, it is about why normal cast bullet loads almost all cast bullet shooters use don't shoot as accuately above a certain velocity as they do below at or below that velocity. THAT is the question I am preparing to answer by shooting over 500 rounds, using 2 different cast bullets, 3 different powders (4895, RL15, H4831SC) loaded in 1 gr increments to give velocties from 1800 through 2500+ fps with each powder and bullet. Identical loads will be fired through 3 accurate rifles of .308 Winchester and each 5 shot string of a particular load will be chronographed and the group measured. Each through a rifle with a with a different twist; 10, 12 and 14".

The test IS NOT to show which rifle is more accurate but at what RPM accuracy deteriorates. Thus the test I am doing is to show at what RPM accuracy deteriorates in each of the 3 rifles with the 2 different bullets loaded over 3 different powders. Given the different twists of the rifles the RPM will be different for each rifle at any given velocity. If accuracy deteriorates in the 10" twist at 2000 fps but doesn't in the 12 and 14" twists then that is an indicator that RPM is the culprit. If at 2200 fps accuracy is still worse in the 10" twist and deteriorates in the 12' twist also but doesn't in the 14" twist then that is even more of an indicator that RPM is the culprit. Then if at 2400 fps accuracy deteriorates in the 14" barrel and we compare the RPM when accuracy deteriorated in all three twist barrels and find that it is close to the same then that would be a good bet that RPM was the real culprit.

So Bass, if you insist my test is "fairly useless" then I challenge you to come up with a comprehensive comparable test to show us how "the HV guys are changing the stereotype." Please SHOW me/us how your '06 holds accuracy from 1800 fps through 2600+ fps and that best accuracy DOES NOT come in the RPM threshold with that 154 gr LBT bullet but at the higher velocity/RPM of 2500+ fps. The choice of alloy, lube, size, barrel bedding or any of the other "anal" things you want to do are ok with me. Pictures of targets and chronograph results please. Shouldn't take more than 10 five shot strings to cover 1800 to 2600+ fps. The guantlet is at your feet. All you have to do is pick it up.

Nothing like a friendly little shoot out, eh?

Larry Gibson

mainiac
12-02-2007, 06:46 PM
Thought i might chime in here with a test that im going to make. In previous posts, i alluded to a 22 hornet that shoots up to 2800 f.p.s. with acceptable accuracy. Im about to start testing my 222,s. The difference is that the hornet has a 16 twist, and my 3 222,s have 14 inch twists. Will my deuces shoot as high a velocity as the hornet will, with the same bullet? My benchrest guns have barrells with the slowest twists possible. 15 inch, with 1.080 jackets in 6mm, and 17 twist with 1.000 jackets in .30 caliber. These are on the bare edge of stabilization, but it is the most accurate way of shooting registered br. Anyway, when i get my test done,i will report back. BTW, one of my 222,s is a old sako vixen,with micro-groove barrell. This should be intresting.

felix
12-02-2007, 07:18 PM
It might be best to set a delimiter, such as an "x" inch group. So, what is the top speed where that group size is still guaranteed intact? Must choose a group size that all contested guns can do at some minimum velocity, range. Shorter the range the better, to eliminate the environment as much as is possible. Prolly no more than 80-100 yards, eh? I feel there is no real need to show targets in this instance because only honest folks will be participating. ... felix

FISH4BUGS
12-02-2007, 07:46 PM
As a machine gun shooter, RPM means rounds per minute. The ONLY factor to consider!

felix
12-02-2007, 07:49 PM
Agree whole heartedly when fishing for bugs. I went fishing once for sunfish, and brought up a damn submarine. ... felix

joeb33050
12-02-2007, 08:06 PM
Bass

The question here is rather straight forward;

Why is it the average reloader when he gets a regular mould from Lyman, RCBS, Lee or Saeco for his rifle can get accuracy at a certain velocity yet loses accuracy above that velocity?

With the 30-06 for expample he gets good accuracy in the 1700-1900 fps range but above that he gets poor accuracy. He casts the bullets of WWs or an alloy like #2 as mentioned in Lyman's or RCBS cast bullet manuals and uses normal loading techniques as per the manuals. I believe the reason is that above a certain threshold of RPM (the threshold is a range of velocity of 125-140,000 RPM not a specific "limit") accuracy deteriorates with such cast bullet loads as the increased RPM accentuates the inbalances in the bullet (caused during casting, by poor fit, excessive obturation during accelleration, etc.). The increased RPM causes the yaw, pitch and wobble to be increased and accuracy suffers as the higher the velocity the higher the RPM.

I'm attempting to answer that question; is that too hard to understand? I think it is not as you've already conceded that RPM does have an adverse effect on accuracy of cast bullets; " So your test to find best "average accuracy" with what's "reasonably" available off the shelf or steps that are taken is fairly useless. If you want to prove "easiest accuracy" that a slower twist is more .... "idiot proof" and minimizes errors as a reloader and shooter of cast, save your components, I'll give you that." BTW; the use of the slower twist is to keep the RPM under the threshold while attaining a higher velocity. Our example shooter is not going to get another barrel for his favorite '06, he wants it to shoot as is.

Now as to the rest of your last post; yes you can get around the RPM threshold by getting "anal". There are a number of things one CAN do, but the average cast bullet shooter isn't going to do them. He neither has the equipment, the knowledge nor the desire. He just wants to cast bullets, load them in the rifle that he has and go shoot them. He is not going to get a different rifle, new molds, a lot more casting equipment or make some exotic alloy. He just wants to know why his bullets won't shoot accurately above 1900 fps or so out of his '06. And by just casting and shooting regular bullets he is not going to get accuracy above the threshold, now is he. The reason he won't get accuracy above a certain velocity with his 10" twist '06 (or any other rifle of 12" twist or faster) is EXACTLY what we are talking about, isn't it?

The question isn't about getting anal is it, it is about why normal cast bullet loads almost all cast bullet shooters use don't shoot as accuately above a certain velocity as they do below at or below that velocity. THAT is the question I am preparing to answer by shooting over 500 rounds, using 2 different cast bullets, 3 different powders (4895, RL15, H4831SC) loaded in 1 gr increments to give velocties from 1800 through 2500+ fps with each powder and bullet. Identical loads will be fired through 3 accurate rifles of .308 Winchester and each 5 shot string of a particular load will be chronographed and the group measured. Each through a rifle with a with a different twist; 10, 12 and 14".

The test IS NOT to show which rifle is more accurate but at what RPM accuracy deteriorates. Thus the test I am doing is to show at what RPM accuracy deteriorates in each of the 3 rifles with the 2 different bullets loaded over 3 different powders. Given the different twists of the rifles the RPM will be different for each rifle at any given velocity. If accuracy deteriorates in the 10" twist at 2000 fps but doesn't in the 12 and 14" twists then that is an indicator that RPM is the culprit. If at 2200 fps accuracy is still worse in the 10" twist and deteriorates in the 12' twist also but doesn't in the 14" twist then that is even more of an indicator that RPM is the culprit. Then if at 2400 fps accuracy deteriorates in the 14" barrel and we compare the RPM when accuracy deteriorated in all three twist barrels and find that it is close to the same then that would be a good bet that RPM was the real culprit.

So Bass, if you insist my test is "fairly useless" then I challenge you to come up with a comprehensive comparable test to show us how "the HV guys are changing the stereotype." Please SHOW me/us how your '06 holds accuracy from 1800 fps through 2600+ fps and that best accuracy DOES NOT come in the RPM threshold with that 154 gr LBT bullet but at the higher velocity/RPM of 2500+ fps. The choice of alloy, lube, size, barrel bedding or any of the other "anal" things you want to do are ok with me. Pictures of targets and chronograph results please. Shouldn't take more than 10 five shot strings to cover 1800 to 2600+ fps. The guantlet is at your feet. All you have to do is pick it up.

Nothing like a friendly little shoot out, eh?

Larry Gibson

I believe that "guantlet" is more properly spelled "gonetlet". Or perhaps "gontlet". Could it be "gonetlette"? Never mind.
joe b.

Larry Gibson
12-02-2007, 09:22 PM
felix

I disagree. If we were testing to see which load was the "most accurate" that might be a good idea. However, what we are looking for here is the accuracy capability of a certain twist over a broad range of velocity. Lets' take the '06 with 10" twist as an example. Let's say we work loads up in 1 gr increments each with 5 shots. The velocity and group sizes look like this;

fps group (inches)

1797 1.2
1869 1.2
1948 2
1981 2.8
2051 4.1
2102 2.4
2183 3.1
2283 3.4
2392 3.7
2438 4.3
2496 5.7
2592 8

What we see is very obvious (these are actual velocities and group sizes fired in a 30-06 with Bass's LBT bullet over increasing charges of 4895 BTW). As velocity increased so did accelleration. As the velocity increased so did the RPM. You can see from the increasing group size that somethig is causing the inaccuracy. I believe this is evidence that RPM is accentuating the defects/imbalances in the bullet. The defects in the bullets may have also increased because of acceleration and increased presure. What ever the reason for the defects it is the RPM that makes accentuates them decreasing accuracy.

The following is using Bass's LBT bullet over RL19;

2431 3.3
2493 3.4
2526 3.5
2588 5.3
2614 4.1
2660 5.25
2724 14

We see here that the slower burning RL19 gave slightly better accuracy through 2526 fps. But the point is; the best accuracy with that bullet in a 10" twist barrel was down at 1790-1950 fps. That is right smack dab in the RPM threshold.

That is why I'm only looking for the RPM when accuracy goes south.

Larry Gibson

Bullshop
12-02-2007, 09:39 PM
You guys have got me wondering how all this applies to a boolit in a sabot. My tuned in load with the 06 has a 55 gn boolit doing 4100 fps from a 1/10" twist. How many rpm's is that? In developing the load it went to 4300 fps max velocity according to pressure indications but best accuracy was at 4100 fps comming up from the mid 30's. Thats about what you see from most any bullet load where the best is at just a bit under max, but this is still with a boolit.
So is this rpm over the threshold, and if so why does it work?
BIC/BS

felix
12-02-2007, 11:33 PM
Either way looks OK to me, Larry. On the first showing, 2350 would be the cutoff. On the second, I'd say 2500, but I would reshoot the 2588 group just to see if 2600 could be obtained. ... felix

felix
12-02-2007, 11:38 PM
Dan, the sabbot is the dealie that is taking on the twist function because of its outer diameter. The inner diameter object, the bullet/boolit, does not see the destructive force of the lands, and also because of the lessor diameter itself it does not have the same outward thrust from the center. Need to treat the inner object as if it were shot in a barrel made for it, such as a 224 barrel. 22s as you know can rotate much faster for the same accuracy as 30s because of the diameter. ... felix

45 2.1
12-03-2007, 07:56 AM
Dan, the sabbot is the dealie that is taking on the twist function because of its outer diameter. The inner diameter object, the bullet/boolit, does not see the destructive force of the lands, and also because of the lessor diameter itself it does not have the same outward thrust from the center. Need to treat the inner object as if it were shot in a barrel made for it, such as a 224 barrel. 22s as you know can rotate much faster for the same accuracy as 30s because of the diameter. ... felix

I've been reading this thread and LMAO. Everything said is a symtom of something else. Bullshop has a boolit going so far over the RPM theory that its ridiculous. Now the theory is that its destructive forces that cause the problem. Either define what the theory says or quit trying to evolve it. Its the material strength folks. Introduce a stronger boolit or bullet and the parameters change.

joeb33050
12-03-2007, 08:04 AM
The M14/Palma business seems to show that accuracy was good, velocity increased and accuracy decreased, twist was reduced and accuracy came back at the higher velocity.

The results with BASS bullets seem to show that as velocity increases beyond some point, accuracy decreases.

There's a jump here to making the RPM the cause of the accuracy decrease.

Some talk about "over stabilization", yet I've never believed it because of the good results with short bullets in 30/06 10" twist. And others.

Most of us believe that cast bullets don't shoot as accurately at high velocities. Doesn't mean that it can't be done, means that very hard bullets and tricks are required that are beyond the reach of we mere mortals.

I'm trying to think of a test that would look at RPM.
Let's say we captured one of those experimenters and got him to develop a short hard bullet
accurate load in a slow twist rifle chambered for a certain cartridge.
Then we tortured him until he made a fast twist rifle chambered for the same cartridge and shot the same load in that fast twist rifle.
If the accuracy fell apart in the fast twist rifle it would seem reasonable to suspect the RPM as the culprit.
The immediate situation is that we all have fast twist rifles in which we could try the same load, but those pesky experimenters chamber their rifles for the 30 X 47 or 30BR. How do we get the same MV ? It would be best to deal with one action, one chambering reamer/throating reamer and two barrels.
What we have is our rifles and Quickload, that could give us the charge required to duplicate the experimenter's MV.
It would also be good to make the experimenter supply us with some bullets, so that that variable is out of the equation.
I would think that if three of you tried the experimenter's bullets with a Quickload charge at ~ the same MV, a couple of five shot 100 yard groups would tell the story.

Say we could find an experimenter with, for example, a 30 X 47 rifle with a , say, 17" twist. Imagine that he used 155 grain HTWW (+1% tin) bullets lubed with LBT Blue at 2650 fps and shoot accurately.
His bullets are turning 112,235 RPM.
Say we could force him to send 25 bullets to each of three willing participants, who had rifles of 10" and 12" twist, and that we got Quickload loads for their rifles giving the same MV.
Now say that those three participants shot three five shot groups each with those loads.
2650 fps 10" twist = 190800 RPM
2650 fps 12" twist = 159000 RPM
I think that 2650 fps with a 155 grain bullet is going to require a strong 308 or 30/06 rifle.

So, does this make sense?
Where oh where could we find such an experimenter?
joe b.

Bass Ackward
12-03-2007, 08:29 AM
We see here that the slower burning RL19 gave slightly better accuracy through 2526 fps. But the point is; the best accuracy with that bullet in a 10" twist barrel was down at 1790-1950 fps. That is right smack dab in the RPM threshold.

That is why I'm only looking for the RPM when accuracy goes south.

Larry Gibson


Larry,

Thank You very much. Great point, I now see your problem. You just got the diagnosis wrong cause you can't let the RPM thing go out of your head. That is my other point.

The RL19 showed you that the problem was pressure or harmonics, not RPM. Do you know how I come to that conclusion?

Because if it were RPMs, ALL powders would produce the same size groups at the same RPMs. If the lead was flying apart, then flying apart is flying apart. All bullet designs would shoot the same size groups. All weight bullets would have the same HV potential.

There it is. RPM is twist related and NOT powder dependent, but pressure is.

What that experiment showed you is EXACTLY what I told you a while back. Now maybe the RL19 would have still worked had you sized differently. So your problem can be alignment OR pressure. I don't know the gun. If you throat was vastly larger than .3095, you might have needed a larger bullet diameter. If your throat peaked at say .311, then you would be able to handle a .308 diameter and your results would have been different again. Or maybe you needed a slightly harder bullet. Or maybe dropping down to RL22 / 7828 and you would have been in high heaven. Or just changing your tip pressure. Or it could be any of the above.

But you don't get lucky very often with just throwing a charge and shooting the same diameter and hardness that you did down below when accuracy was easy.

If the problem really WAS RPMs, then no load related factor, no gun related factor would change the end result and all groups would be the same at the same velocity level. Make sence?

Take that 311466 and get you a can of 7828, start at 48 grains and come on up with it if you can size that BIG thing down and still have lube grooves. Other wise, I can mold you up some bullets after the holiday and you can try again. If you have to size bigger for what ever reason, your top velocity ceiling will be lower than it otherwise would be.

Or I can send you my mold if you promise to give it back in a timely manner. I am worried that you get this working and I will never see it again. I never trust SFCs cause they are always sceeming to make E-8. :grin:

felix
12-03-2007, 11:20 AM
What you said, Bob, is right on! It is the total material strength and, naturally, its consistency throughout. Nothing to laugh about except our gyrations to create accurate boolits. The whole process is a joke, and that is why casting is such a great hobby. ... felix

charger 1
12-03-2007, 11:43 AM
I think if mold and person doing the casting, sizing and lubing know their bees wax, which includes throats etc we have limited ourselves to lower revs than need be. Uncle Veral says so to[smilie=1: When Douglas sent me a 24 twist rather than a 34 I told Mr Smith as the mold was being made that my twist might be to quick. His response was."If you got the correct boolit there is such a thing as to quick a twist?"

45 2.1
12-03-2007, 11:44 AM
What you said, Bob, is right on! It is the total material strength and, naturally, its consistency throughout. Nothing to laugh about except our gyrations to create accurate boolits. The whole process is a joke, and that is why casting is such a great hobby. ... felix

While there are some trying this, it would be nice to remember the basic rules. We have a statement from Larry Gibson:

Woke up this morning and since the wife was sleeping in I turned on the Mag 20, put some 60/40 WW/Lino alloy in it, degreased two Lyman 2 cavity moulds (311291 and 311466), put a pot of coffee on, turned on some smooth jazz on the radio and commenced to cast 16 lbs worth of bullets.

He planned on running these from 1800 fps up to about 2600 fps. there is quite a difference in pressure range from start to end, but do we see any alloy difference or heat treatment. None that he stated. The idea that previous experimenters was to match alloy strength to pressure. NOT being done here and he expects results, (or to prove his point). This is why i'm laughing. If he is serious about proving RPM theory to a reasonable conclusion, he shouldn't break the basic rules. From an alloy thats strong enough to one that is seriously deficient (in strength and alloy constituents) for the pressure level involved. Veral Smith wrote some books on this for the uninformed. I'm sure that something will come back about this.

Bullshop
12-03-2007, 01:39 PM
Felix
OK I see its not just RPM then its also caliber related. So then the smaller the caliber the higher the rpm limit, and the larger the caliber the lower the rpm limit, if the boolit material is the same, is that it?
In that case the 6.5 cals should handle a higher rpm than the 30 cals. I am remembering when the cruise missle came out for the 6.5's and everybody was having fitts trying to get it over about 1700 fps and boolits were wizzing off to never never land.
Seems looking back thats what started the first big debate about rpm threshold. My friend Starmetal was in the thick of it and defending a position against it. He had me send him some 72gn .225" boolits to try in 7" twist. The boolits were acww but should have been harder even so he did perty good with them. If he had had the mold the play with there may have been a more interesting conclusion but at that time the discusion fizzled out. Perty good stuff here anyway. With all the stuff from both sides of the fence we are all learning and forming new idea's of things we just gotta try.
Blessings
BIC/BS

felix
12-03-2007, 02:15 PM
That is all correct what you said, Dan! Keep in mind, though, and, as Starmetal Joe knows, the grooves have to be cleaner the further up the RPM ladder we go. The boolit has to have a firm grip on the lands throughout all speed ranges for any RPM "proof/spoof" to be genuine. This is why your plastic sabot does so well when compared to lead from shot to shot. So, keeping the barrel clean is a major problem here, but it has to be taken into account for realistic measurements as well. Nobody, but nobody, is going to clean a gun between shots. Nobody would shoot for fun otherwise. ... felix

Bass Ackward
12-03-2007, 03:38 PM
You guys have got me wondering how all this applies to a boolit in a sabot. My tuned in load with the 06 has a 55 gn boolit doing 4100 fps from a 1/10" twist. How many rpm's is that? In developing the load it went to 4300 fps max velocity according to pressure indications but best accuracy was at 4100 fps comming up from the mid 30's. Thats about what you see from most any bullet load where the best is at just a bit under max, but this is still with a boolit.
So is this rpm over the threshold, and if so why does it work?
BIC/BS


Dan,

The RPMs of your sabot are 295,000.

It works because the sabot feels all the pressure and not the lead. You bullet is not deformed from pressure so it flies well and you thus have the flexibility to match accuracy to the harmonic sweet spot at 4100 fps.

And what kind of accuracy are you getting at this point?

felix
12-03-2007, 04:09 PM
All true. ... felix

Larry Gibson
12-03-2007, 04:15 PM
Bass

"Because if it were RPMs, ALL powders would produce the same size groups at the same RPMs. If the lead was flying apart, then flying apart is flying apart. All bullet designs would shoot the same size groups. All weight bullets would have the same HV potential."

You miss the point. First of all lets take a regular cast bullet that you or I cast. Is it perfectly balanced ? No it is not. If it were perfect and was not further damaged in the barrel from the rifling and obturation due to accelleration then every bullet would fly straight and true into the same hole. It is the imperfections in balance of the bullet that cause inaccuracy. I will grant you that barrel harmonics plays a part also but I talking strickly the bullet here; perfect bullets would fly true, imbalanced bullets do not. It is RPM during flight that causes these imbalances to adversely effects accuracy. Yes, different pressures and time/pressure curves cause barrel harmonics. The example given with your bullet and load is not the only combination that this effect of RPM adversely effecting accuracy occurs in. It occurs with EVERY medium and slow burning powder bullet combination that I've ever shot. And that sir has been a lot of combinations over the years.

Now that being said let us move on. If you notice my test is set up for 3 different powders, one of which is your previously stated powder to use. Also notice I am using 3 different rifles with barrels of different manufacture and contour. I surmise the harmonics for each is going to be different. Wouldn't you agree? However, I will do as you suggest and get some 7828 (a different powder than previously suggested as best) and start at 48 gr (is that for a .308 or '06?) and work up with 311466. There is still plenty of lube groove and lube left after sizing to .311 and .309 (.311 is on the left, .309 on the right - picture is of culled out bullets to be used for sighters). No need to send me the mold, at this time anyway.

Speaking of your LBT bullet; in both the .308 and the '06 your LBT bullet shot it's best accuracy down in the RPM threshold with 3 different powders. There was no doubt some different barrel harmonics between the different powders and the 2 different barrels there. But the results were the same; best accuracy was ALWAYS within the RPM threshold.

Now so what if the barrel harmonics are different. What do I mean? Lets say that we load different powders over a broad spectrum of pressure from 1700 fps to 2600 fps in the 10" twist '06. Using 4895 best accuracy is 1" with RL19 it is 1.3", with H4831SC it is 2.2" and with 7828 it is 1.9" moa at 100 yards. If we were comparing "best accuracies" we would assume the 4895 load to be the "most accurate". This is all regardless of velocity differences or RPM but just comparing the "accuracy" of the different loads. But what if we only compare the "best accuracy" velocity of one powder in one barrel to the velocity levels of the lessor accurate loads in that barrel with that powder. Would that not then be a valid comparison?

Thus we are not going to compare "best accuracy" between different powders but to determine the velocity (RPM) at which best accuracy is in each barrel with each powder. The different harmonics created by different powders in different barrels is then negated as the size of the group is not important, only how that size relates to the other groups fired with that one powder in that one barrel. In other words; if all the powders produce the "best accuracy" (regardless of the "best acuracy" group size disparity for the individual rifles) in or under the RPM threshold then the RPM threshold will be substantiated. Again, since each powder in each rifle is only being evaluted against itself, barrel harmonics are negated. The size of the group is imaterial as it is the trend in the sizes of the groups that is being measured.

If all of that is to confusing then let's wait and see what the test results are.

Larry Gibson

Larry Gibson
12-03-2007, 04:36 PM
45 2.1

Laugh all you want but it is you who fail to understand the question. The question is this as previously stated;

"The question here is rather straight forward;

Why is it the average reloader when he gets a regular mould from Lyman, RCBS, Lee or Saeco for his rifle can get accuracy at a certain velocity yet loses accuracy above that velocity?

With the 30-06 for expample he gets good accuracy in the 1700-1900 fps range but above that he gets poor accuracy. He casts the bullets of WWs or an alloy like #2 as mentioned in Lyman's or RCBS cast bullet manuals and uses normal loading techniques as per the manuals. "

I'm not breaking any basic rules, I'm answering the question. Besides, many here say to shoot them soft at HV and many say to shoot them hard at HV. So what is the "rule". Lyman shows 2800+ fps in the .308 with 311466 and makes no mention of using a harder bullet than #2 alloy for that. Our intreped reloader reads that and thinks he should be able to do it accurately. But you bring up a point; so perhaps chapter two of the test will be to use WQ's WSS and linotype cast bullets and shoot them with the loads where accuracy falls off to see if accuracy can be sustained at/to a higher velocity/RPM.

I say that the best accuracy with cast bullets will come in or below the RPM threshold (regardless of alloy) and am conducting a comprehesive test to demonstrate that. Now within the context of your experience show me one of your loads that shoots its best accuracy above the RPM threshold. Kindly don't tell me what I should do (as Bass did with the gauntlet) but show me what you CAN do. The gauntlet has been passed to you.

Larry Gibson

Larry Gibson
12-03-2007, 04:38 PM
Bullshop

I forget, was that saboted bullet jacketed or cast?

Larry Gibson

Bullshop
12-03-2007, 04:42 PM
BA
I would say about 90% will go into 1 1/2" at 100 yards, 90% of the outsiders will go 2", and the ocasional wild shot out to 3" or so. Keep in mind that I am not weigh sorting and that may account for the small % wild shots.
Still usable accuracy at a velocity I have not been able to get close to with the same boolits in a 22 bore.
BIC/BS

Bullshop
12-03-2007, 04:49 PM
Larry
The sabot load is with a boolit from a CBE mold for a 55gn Luverin style. They get sized in a nose first push through to .224" to fit the sabot but no lube or gas check. They are then seated into the sabot using an RCBS lube sizer with a .308" die installed and a TP that fits the boolit nose correctly. This is the best method I have found for preping the boolit/sabot for loading.
BIC/BS

Bass Ackward
12-03-2007, 06:05 PM
That is all correct what you said, Dan! Keep in mind, though, and, as Starmetal Joe knows, the grooves have to be cleaner the further up the RPM ladder we go. The boolit has to have a firm grip on the lands throughout all speed ranges for any RPM "proof/spoof" to be genuine. This is why your plastic sabot does so well when compared to lead from shot to shot. So, keeping the barrel clean is a major problem here, but it has to be taken into account for realistic measurements as well. Nobody, but nobody, is going to clean a gun between shots. Nobody would shoot for fun otherwise. ... felix


Absolutely! Or the rifling height needs to be taller. :grin:

We have covered this ground all before more than once or twice. But it's hard for some to piece it together.

I will add that when some believe that stripping is the issue from too soft of a metal, that it isn't necessarily the case, fouling or harmonics are the more likely culprit. In fact, my winter lube tests with a chronograph lead me to believe that fouling and reaching harmonic nodes are a much higher reason for failure than stripping. Hardening bullets alone is no guarantee. Take steps to slow pressure, reduce the fouling and soft metal can go much higher than people think.

Velocity tells the tale. If you strip, you pass gas. The lower pressure results in declining velocity in a string of shots or declining velocity in groups. If your velocity is staying up and ES are still good, your inaccuracy isn't from stripping and bullet hardness may not solve all your problems. I find that if I work out the issues with soft metal first, and THEN harden, I get much more consistent accuracy over longer secessions too. Bullet hardness alone can mask other problems that result in a lower top end than otherwise would be possible. Or accuracy for 5 shots that expand with subsequent groups.

It's the lube fouling that causes my winter lube problems too with soft, olgival design bullets and thick or frozen lube (fouling) up the pipe sizing down / deforming my bullets. If I harden the bullets, accuracy can come back with minor tinkering. If I minimize lube, I did better. But unable to beat the temperature characteristics of lube, I changed bullet designs to one that possess a shoulder to deal with fouling now. Less accurate in the summer, but much more consistent in the winter without hardening. This experimentation was what lead to my theories against most stripping.

In the end, all guns will have a limit based on mechanical conditions that will require something different individually or in combinations from one gun to another. One gun may have to settle for 2400 fps where the next gun cranks the same bullet to 2700 fps. Joe Starmetal cheats using gas operated actions that cut muzzle pressure too. :grin:

Bass Ackward
12-03-2007, 06:55 PM
Larry,

I am here to tell you I was lucky. My first HV group took all of 3 powder charges. I got cocky and my next attempt never happened. My knowledge came from studying that first attempt.

Harmonics with jacketed are barrel movement of a few thousands moving at high frequency. Changing powders changes harmonics. 4895 with a 150 grain jacketed in a 30-06 opens and closes every three grains from 40 grains up to 49. One of those will be better than the others. If it isn't, you change powder until your barrel harmonic coincides with a frictional node. Change powders, you change harmonics.

Bore friction, fouling, finish and several other factors play a part which is why one guy needs 4895 and the next may need 4064 with the same bullet.

But with lead, your friction is WAY less than jacketed. So your barrel swing may be twice as slow covering the same distance. Any fouling can alter velocity enough that you don't exit at the same point which changed your harmonics. So for argument sake, let's say your lead could withstand the deforming pressure of 4895, you may only get one attempt at a group in that same 9 grain span. Or none. And going to 4064 may do nothing to bring it in, it may take 4831. That's why bedding can make a difference if it cuts the size of the swing.

You need "bolder" powder swings to achieve the necessary change in harmonics if it's going to happen for you at all. Not simple load change as you would do with jacketed. Or bullet hardness change which may require a smaller size. The harder I have gone with my bullets, the smaller I have needed to be. When you find that "reasonably" accurate load, now you have to tweek it to bring it in. There will always be a .... cusp for each caliber / rifle / bullet and load. The greater the case capacity, the smaller this cusp will be. The slower the powder that you can achieve harmonics with, away from this cusp, the less effect any hardness or sizing or any other variable will make a difference and thus the better or more consistent accuracy you will enjoy.

But if you get over 2" groups, you are experiencing pressure related problems that may be cured by a hardness increase. The 7828 was an attempt to get an easily ignited powder to be away from the cusp. One thing is for sure, if you were throwing too much pressure for my 150 grainers with RL19, your heavier bullets are going to need a slower option yet. That was the reason for my recommendation looking at your data. Not just to separate you from your cash.

And the 48 grain was a 308 recommendation. Look .... the search can be done with 2 shot groups at first. Nothing fancy, just two shots tells you whether you are close or need to make a bold move in some factor. Then tweek with more shots.

Junior1942
12-03-2007, 07:40 PM
A fact: all of my 1 - 9 & 1 - 9.5 twist rifles and pistols start getting fliers, usually with commas, when the rpm of the cast bullets hit 110,000. Below that, at lower velocities and rpm, I get nice groups, just like I get in my 1 - 12 twist cast bullet rifles at much higher velocities.

Larry Gibson
12-03-2007, 11:09 PM
Bass

Great, 48 gr 7828 as a starting load it will be. I've got to disagree on the 2 shot test. Yes it will tell you what load gets you to HV. But it will not show any consistancy of load or give a meaningful measurement of group size/accuracy either across the chronograph or on the target. What we are looking for is a range of groups from the low end of the RPM threshold to a much higher RPM level above the threshold, specifically that velocity where accuracy deteriorates.

You don't seem to understand; the question is not to develop an acceptable HV load. I have acceptable HV loads, it's just that they are not as accurate as when that bullet is shot down within the RPM threshold. Where does accuracy deteriorate (just deteriorate, not go rat crap bad) and is the reason for that deterioration a function of RPM's effect on the imbalances of the bullet. A higher RPM at a given velocity should produce less accuracy if that is correct. That's why we are using 3 different twists. If accuracy with the same load holds at a higher velocity using a slower twist then RPM is the reason.

You must have a potful of bad barrels. When working up loads for jacketed bullets I've found accuracy improvement as we increase pressure (increases the burning efficiency of the powder) to be pretty much a linear function until maximum pressures are reached. I've not had the "opening and closing" effect "every 3 grains" that you describe. That is with numerous lots and makes of 4895 and a multitude of other powders.

I had to look "cusp" up in the dictionary and still am not sure of what you mean. Could you restate that?

Larry Gibson

Larry Gibson
12-03-2007, 11:21 PM
Bass

For sake of discussion; take a rifle that is very accurate with a jacketed bullet load. The "harmonics" must be pretty good right? Now take some bullets used in that load and drill a small hole in the side of them. Load the drilled bullets exactly the same as the load before and shoot them. Accuracy will not be as good, right? The reason being is the bullet is unbalanced and the RPM is making them wobble, yaw and pitch giving poorer accuracy than the undrilled bullets. Oh, you say the harmonics got messed up. Ok, maybe so. If so then lets go back and rework the load to retune the "harmonics" with the drilled bullets. Want to bet any money that the drilled bullets will not shoot any better no matter how much you tune the harmonics of the barrel? I'll match the bet and give you odds they won't because the RPM will have the same effect on the unbalanced bullets in flight no matter how much you tune the harmonics of the barrel.

Larry Gibson

Ricochet
12-03-2007, 11:34 PM
If you strip, you pass gas.
How'd you know?! :eek:

Bass Ackward
12-04-2007, 08:09 AM
How'd you know?! :eek:


Awh, it was just a gut feeling.

Bass Ackward
12-04-2007, 08:40 AM
Larry,

If you think the bullets you have bought over the years that have established your knowledge base have been any better balanced than good quality molded bullets, then there is no hope. And I thought I was a rule breaker.

I will tell you this, I will bet that some of the best groups you ever turned in were done with outta balanced jacketed bullets that didn't even weigh the same. 100 yards to a rifle is sorta like 25 yards to a handgun and just about anything can be shot accurately. It's what happens out beyond there that makes a load to me and when weird stuff happens after they lose velocity.

Please don't watch any football games either. There is a ball that has strings on one side to make it outta balance. What you will find is that the faster it is rotated and the faster it is thrown, the better stabilized it be and the farther it will fly accurately. You won't be able to enjoy the game now that you know that.

I got a total of 11 groundhogs this year with lead out to just shy of 400 yards. I can't tell you how good your going to feel when you make that happen. That's why I am routing for ya.

But I'm done for now. You burnt me out. Let's see how your tests go.

Larry Gibson
12-04-2007, 11:39 AM
Wow, I am just plumb amazed!

Guess I've really missed a lot in the shooting world. I hadn't noticed that all the accuracy bench rest records were shot with cast bullets. I hadn't noticed all the high power shooters were using cast bullets out to 1000 yards. I hadn't noticed that all the long range varmint shooters were using cast bullets. After all a "good quality moulded bullet' is much better than all those factory bullets I have bought over the years. Silly me, there I was buying Sierra MKs along with lots of Hornady, Speer, Berger and Nosler match bullets thinking how great the quality was! I'm sure glad to be enlightened on how poor quality they are. Perhaps had I used cast bullets I would have really "cleaned" everyones clock in those 800, 900, and 1000 yard Palma matches. I guess I should have been shooting cast bullets "across the course" in an M14 shooting Service Rifle, then I may have made High Master instead of just Master. Oh silly me........I guess Bass is right; "there is no hope" for me! I don't really think a cast "moulded" bullet is of the same quality as a Match King or other match bullet or quality jacketed hunting bullets for that matter. I don't think anyone else really does either including Bass. One may get some pretty decent accuracy at HV with cast bullets (Bullshop with his saboted cast bullets for instance) but there is no way a cast bullet is going to shoot as accurately as a jacketed match bullet. I found that statement incredulous to read, there is no hope for me?

Seriously, I ask for the doubters to show me that their cast bullets are more accurate above the threshold than in or below it and do they? No, I'm told what I should do. I ask the doubters for a simple 50 shot string of groups that they shoot to show me what they say can be done and do they? No, I'm told about footballs. When is the last time a QB pitched one out above the RPM threshold? I guess THAT comparison then really is relevent and makes sense doesn't it?

Let me see; "11 groundhogs with lead out to just shy of 400 yards". I say great! A 3 moa load can do that. I have shot lots of rock chucks out to 400+ yards with M1A/M14s using 2-3 MOA ammo. I've shot rockchucks out to 400 yards with a 311041HP out of my .308 CBC (2 moa capable all day long) but it was only at the top end of the RPM threshold. That doesn't mean a darn thing germain to this question. If Bass slows that same cast bullet down (I'm assuming Bass meant with one of his HV loads that excedes the RPM threshold) to within the RPM threshold and it shoots more accurately then the RPM theory is valid.

Anyone notice none of the doubters have said that their bullets won't shoot any better within or below the RPM threshold? Could it be they really know it's correct? In all fairness to them I really don't think they understand. Seems they all think the question is; "you can't get any kind of accuracy at HV". The resposes from them, from my impression anyway, seems to lean that way. That is not the question however. You can get some pretty decent accuracy at HV. I can and you can with not too much anal work involved if you understand how to do it. They also think I don't know how to do it but they are wrong. The question is; How come a bullet won't shoot as accurately above the RPM threshold as within or below the RPM threshold. That is the question pure and simple. The question is about whether a bullet, any cast bullet, will shoot more accurately above, within or below the RPM threshold. Doesn't matter whether the bullet shoots good above the RPM threshold, does it shoot more accurately within or below the RPM threshold. Not to hard for most of us to understand though some are obviously having problems grasping the concept.

The test will be done. I shall report back.

Larry Gibson

subsonic
12-04-2007, 05:42 PM
Reading with interest....

I'd sure like to see some of those drilled bullets, or boolits otherwise modified, so that they are intentionally unbalanced, shot in 10, 12, and 14 twist guns at the same speed, to see how they group.

I'd also like to see what happens as twist slows further to 16, 18.... now you should be able to really make those boolits sing.

Hmmm...

The test would be to push some balanced bullets to the same RPM, with higher velocites in those slower twists.

felix
12-04-2007, 06:09 PM
balanced bullets = BR condoms @ 20 cents (???) per. A deep pockets requirement. ... felix

Larry Gibson
12-04-2007, 06:48 PM
Reading with interest....

I'd sure like to see some of those drilled bullets, or boolits otherwise modified, so that they are intentionally unbalanced, shot in 10, 12, and 14 twist guns at the same speed, to see how they group.

I'd also like to see what happens as twist slows further to 16, 18.... now you should be able to really make those boolits sing.

Hmmm...

The test would be to push some balanced bullets to the same RPM, with higher velocites in those slower twists.

Well I can certainly throw that test in after the test with cast bullets. Cartridge is .308 Winchester with 10, 12 and 14" twists. I could do the same in .223 as I have 9, 12 and 14" twist rifles (3 bolt guns, a Contender Carbine and a Savage 24V that doesn't shoot half bad plus I can throw in 7 and 9" twist ARs that shoot really well to). Easier to drill holes in the .30 cal bullets though. could push 125 or 130s at 3,000 fps or so.

Larry Gibson

Ricochet
12-04-2007, 07:30 PM
I'm a disbeliever in a specific RPM threshold, but in no way doubt that it gets harder to get good accuracy as the speed (rotational and translational) goes up. And pressure, which causes bullet distortion, generally has to go up to get the higher velocities that some of you associate with "RPM threshold." I just think there are a lot more factors involved than some arbitrary number of RPMs.

As for the quarterback "rifling" his passes, his unbalanced football is always oriented the same way as it's released. Rarely are bullets all unbalanced exactly the same way, or oriented exactly the same.

mainiac
12-04-2007, 08:05 PM
balanced bullets = BR condoms @ 20 cents (???) per. A deep pockets requirement. ... felix

Felix, my last supply of 118 gr bibbs .30 cost .27 cents apeice.sheesh! This is partly why ive gone cast/informal.

felix
12-04-2007, 09:01 PM
I quit the BR game back in 75 because of expenses. Back then it was time more than money. But that changed pronto in 76 because my 22 was no longer competitive against the 24s coming out all over the place. Why compete when the possibly of placing into some cash was about zero? That is when I branched into real boolits big time, and sorta' gave up on those gold nuggets. ... felix

mainiac
12-04-2007, 09:50 PM
I quit the BR game back in 75 because of expenses. Back then it was time more than money. But that changed pronto in 76 because my 22 was no longer competitive against the 24s coming out all over the place. Why compete when the possibly of placing into some cash was about zero? That is when I branched into real boolits big time, and sorta' gave up on those gold nuggets. ... felix

Ahh, so you was into it when the ppc arrived on the seen. That must have been a revelation to you guys! My guns ALWAYS shot the best when loaded to max-extreme pressures. .22,24,.30,,, dont matter, they all shoot the best when loaded to primer pocket stretching. Same thing with my ruger blackhawks (except for one). What does this say about accuracy? I dont know about harmonics and nodes and all that stuff, never considered it because i was/am always looking for wind cheating speed in my loads.

Bass Ackward
12-04-2007, 10:59 PM
Anyone notice none of the doubters have said that their bullets won't shoot any better within or below the RPM threshold?

The test will be done. I shall report back.

Larry Gibson



Larry,

I have bullet designs with low velocity loads that shoot 3/8s to 1 1/2" in several calibers and bore diameters at 100 yards. I have bullet designs with HV loads that shoot from .2" to 1 1/2" across several calibers and bore diameters at 100 yards. Sometimes, they are the same design, sometimes not and one design will perform better at one end of the scale or the other. But that is just because I haven't done my part and found either a better HV or low velocity load.

One thing is for certain, the HV loads outperform the slow the windier it is or the farther out you go which is the purpose of a high velocity load.

And an accurate load is an accurate load. Period. Was that clear enough? :grin:

Good shooting.

felix
12-04-2007, 11:52 PM
BR work (for real) was always balls-to-the-wall, and then back down and even back up to get the harmonics to play fair (depending on the day). Then we bitch and moan about a barrel destroyed after 700 rounds. Load adjustments at the range only to find the load for that day. Looking back on all that makes one go bezerk over the waste (if you don't make the gains under the table by winning). I came close, but no cigars. Always a better weatherman on the job that hour. Moral of the story: "Don't take your guns to town". ... felix

Larry Gibson
12-04-2007, 11:59 PM
Bass

That's clear enough, any reason we can't see some of the groups and bullets designs. We know you have a camera and can post pictures? And is that 50 shot test (it's only 10 five shot groups) with your bullets and loads covering 1700 to 2600 fps too much to ask?

but the question I really have to ask; what the hell does......

"I have bullet designs with low velocity loads that shoot 3/8s to 1 1/2" in several calibers and bore diameters at 100 yards. I have bullet designs with HV loads that shoot from .2" to 1 1/2" across several calibers and bore diameters at 100 yards. Sometimes, they are the same design, sometimes not and one design will perform better at one end of the scale or the other. But that is just because I haven't done my part and found either a better HV or low velocity load."

.....have to do with answering why our intrepid cast bullet shooter can't get the same accuracy at 2400 fps that he gets at 1800 fps with his 311291 out of his good shooting '06?

Your answer is apparently to tell him to get new custom moulds, change alloy, rebarrel his rifle to a larger capacity cartridge, use slower burning powder, put pressure on the barrel and tune the "cusp" out of it, etc. ad nauseum.

I simply tell him he won't get there from here with 311291 and his 10" twist '06 because the RPM at the higher velocity is causing the inaccuracy.

That clear enough.

Larry Gibson

Bass Ackward
12-05-2007, 09:01 AM
Larry,

Your opinion is valued by me. And because of such, how about doing me a favor? Do one more test and report on it for the board. You are uniquely the candidate here because you are the only one that has attested to have multiple twist rates in the same caliber that I know have been smoothed by shooting. So both should be excellent for this test.

I would like for you to slug your 10 twist and 14 twist for me with a caveat. I would like you to use a good heavy weight oil like say gear weight if you got it to ensure that there is no galling. Use the same heavy oil in both bores so the condition is exactly the same. The thicker the oil, the better the test results will be. If you patch one to remove the excess, then do the other EXACTLY the same, but use a small jag and or patch so fit is very light to leave considerable oil in the bore. Put a tight fitting patch in the chamber to prevent anything going into where you don't want it.

Pound a lead slug into each barrel just to get it to fully engrave and allow the use of a bore guide to protect the muzzle of coarse, but don't push it through yet. Just start one in each barrel.

The test is to start with the 14 twist and push that slug through just as fast as you can. Then before you lose that feeling in your mind, immediately grab the 10 twist and do the same thing. Warning: one is going to fly, and the other will take more time and EFFORT.

Please report on that test and tell us:

1. Which one took the most force to push the slug through?
2. And how significant was the difference?

Then I will ask you a question that you alone will uniquely be able to answer cause you felt what your bullet feels. In fact, this is very educational for anyone that has this capability to test. Feel free to answer these same questions.

Calamity Jake
12-05-2007, 10:48 AM
I don't consider myself to be a dummy by any means and I understand what is trying to be
accomplished here, or at least I think I do!!
And I am learning a lot of good stuff.
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But all this RPM BC is making my head spin!! :bigsmyl2:

Have a good day!!

subsonic
12-05-2007, 10:55 AM
balanced bullets = BR condoms @ 20 cents (???) per. A deep pockets requirement. ... felix

I mean undrilled, reasonably balanced, not BR stuff, although it would be interesting with the BR too.

Larry Gibson
12-05-2007, 03:33 PM
Bass

It is done. I had some 323471s cast of pure lead (old Paco loads) so I ran them through a 314 then 311 die. Lubed both the 10 and 14" twist barrels with some very heavy military gun grease that I always use when slugging bores. Makes the slugs go through slicker than snot. I have two vises mounted on my work bench so both rifles were set up as requested. With both rifles mounted on the bench at the same time I was able to push the slug through one barrel then imediately push the slug through the other barrel without losing that "warm fuzzy".

1. Which one took the most force to push the slug through?

Hard to say as the 14" twist barrel is 5 1/2" longer. The perception was the 14" twist barrel took more force but in reality they were pretty close.

2. And how significant was the difference?

I was pushing longer with the 14" twist which made it appear different. Not any perceptable difference when the slug was moving.

What is your question?

Bear in mind, once again, that in the test we are not comparing the accuracy between the barrels. To do so would only determine the accuracy between the 3 rifles. We are only comparing the accuracy of each barrel to itself. As each barrel produces a different RPM at a given velocity we are looking for the loss of accuracy in that barrel with identical loads as used in the other barrels. If one barrels best accuracy is 2 mos and the other 2 are 1 moa it doesn't matter. What we are looking for is at what velocity each individual twist loses accuracy. Thus if groups begin to open (losing accuracy) at 1913 fps in the 10" twist, 2166 fps in the 12" twist and 2526 with the 14" twist (all with the same loads) then the reason would be RPM is accentuating the defects in the bullets since the RPM for all 3 velocities is 130,000. Now I don't expect the results to be that linear. The Higher acceleration of the faster loads is going to create more defects in the bullets balance and the 14" twist should lose accuracy at the lower end of the RPM threshold. The slower twist, though it does not accentuate the imbalances in flight as does the 10" twist, will have more defects (imbalances) at the higher velocity (higher accelleration or more pressure) to deal with. This is why it is a threshold (125-140,000 RPM) and not a "limit".

Larry Gibson

leftiye
12-05-2007, 05:31 PM
I won't put ALL OF MY EGGSES in any basket, no matter how good it is. All of the other factors that affect accuracy still affect accuracy, don't they? Don't they? Don't they? You can't actually say that this RPM limit operates on its own at all anyway.

Pat I.
12-05-2007, 05:57 PM
I think Larry's test will be excellent but I can't believe Larry and John are the only two guys that have tried working up high velocity loads. I've tried but found that it took a slower twist to get higher speed with the best accuracy. Doesn't anyone else have experiences to share?

Pat

Larry Gibson
12-05-2007, 06:37 PM
I won't put ALL OF MY EGGSES in any basket, no matter how good it is. All of the other factors that affect accuracy still affect accuracy, don't they? Don't they? Don't they? You can't actually say that this RPM limit operates on its own at all anyway.

You are correct with your own answer to your question. There are indeed many things that effect accuracy. However consider that "all of the other factors that effect accuracy" (assuming you are talking alloy, hardness, lube, fit, design, obturation, accelleration, pressure, etc.) take place in the barrel. RPM only effects the bullet in flight outside of the barrel. The "effects" you are thinking about have already happened to the bullet in the barrel before RPM does it's thing which is to accentuate those "effects" that have already happened outside of the barrel. The faster the RPM the more it accententuates those "effects" (actually defects and imbalances). It is the increased RPM which causes more pitch, yaw and wobble in the unbalanced cast bullet thus decreasing accuracy.

Pitch, yaw and wobble happen when the bullet has left the barrel. I think some here have a hard time differentiating between what happens to the cast bullet during the internal ballistic phase vs what happens to it during the external ballistic phase. Hope this explanation helps you and perhaps you can see I've not put my eggs in one basket. I understand there are two baskets. and my eggs are in the second basket. There are three baskets actually, if we want to get into terminal ballistics also. I don't as terminal ballistics is not part of this question.

Larry Gibson

Larry Gibson
12-05-2007, 06:46 PM
Pat

Most of them do it's just that they don't realise it. Look back at many, many posts where they state the velocity of their "most accurate" loads and you'll find they are within or below the RPM threshold. Those who have gotten accuracy above the RPM threshold all admit, or choose not to respond, that their bullets are more accurate in or below the RPM threshold. The proof is there in their own shooting, they just don't see it.

I, too, have gotten what I consider to be reasonbly good accuracy with cast bullets (with only a few designs) at 2400 -2600 fps in the .308 or '06 with 10" twists. However those same bullets ALWAYS shoot more accurately down in or under the RPM threshold. The higher the RPM is above the threshold the less accurate the bullet will be. Maybe the accuracy lost won't be much (if you've the correct design, alloy, fit, hardness, size, acceleration, etc) but accuracy will be lost none the less. I'm sure everyone else's experience is the same.

Larry Gibson

38 Super Auto
12-05-2007, 06:50 PM
Lot of drop in those 22.7 miles.

You might have to use the tang sight to capture that sight picture. :)

Bass Ackward
12-06-2007, 09:03 AM
Larry,

Your results were way different than mine. My question was going to be RPMs or pressure?

When I did it, if I pushed through easy, then both slugs seemed the same. The oil wasn't supposed to make it slick as snot, but to offer non-gauling resistance so the difference would be obvious. If I pushed hard or fast, then the slower twist was dramatically less effort and faster than the fast twist. I did it with 45 caliber 14 and 20 twists I had on hand.

When I was a kid, Ol Earl (friend) told me to find a smooth wall. Face it perpendicular. That is a zero twist. Turn to a 45 degree angle and that simulated a 10 twist and try to walk forward along the wall. Then he said to cut that angle in half and repeat. It seems stupid now, but it was eye opening as a kid and was appartent that twist rate was an impediment to forward motion and the at some point the wall was merely aguide. Different powders would be required to produce the same pressure curve. Shotguns with no twist rate could launch heavier loads with much faster powders than something WITH a twist rate.

And since lead is only so strong, the slower twist rate would have the higher velocity level. And if you can run a higher velocity level, you don't have to rotate it as much either. Therefore, the fast twist would have much higher harmonics from the pressure and the slower twist would be much easier to control. The wall for lead is short (Why taller rifling helps) and the pressure driving it forward wants to push the core straight ahead while the wall wants it to wait and rotate. You need to fight or prevent that stripping. Not rotational force stripping or damage. So it's not rpms to me, but pressure.

That was what I was hoping for you to see.

BAGTIC
12-12-2007, 01:05 PM
The only thing I know about "RPM" is a note in the FAQ section of one of the bullet maker's sites. The question was about why do .22 bullets fragment when fired. The answer was that a commercial bullet (80 grain?) fired in a military barrel rifled for the FMJ Ball (62 grain?) would fly apart. Apparently it's common knowledge among bullet companies.

As for the rest of the "RPM" subject, I am totally ignorant...
and might even prefer to stay that way.
CM

Not likely as the military loads 77 grain Sierra boattails in some of its ammo. Besides the heavier bullet will be propelled slower reducing the spin rate.

There used to be a .22/.257 wildat made by someone in California's central valley was was designed for heavy bullets at high velocity. I can't remember the name. I saw some 80+ grain commercial bullets (Hornady?) made and labeled for for it. It must have worked.

BAGTIC
12-12-2007, 01:13 PM
Modern bullets shoot much better than those of 50 years ago. Closer tolerances and tighter quality controls.

The higher the rpm the greater the deleterious effect of any imperfection, void, off center core, cocked bullet, etc., Higher rpm's will shoot accurately they just require higher quality bullets.

BAGTIC
12-12-2007, 01:15 PM
The only thing I know about "RPM" is a note in the FAQ section of one of the bullet maker's sites. The question was about why do .22 bullets fragment when fired. The answer was that a commercial bullet (80 grain?) fired in a military barrel rifled for the FMJ Ball (62 grain?) would fly apart. Apparently it's common knowledge among bullet companies.

As for the rest of the "RPM" subject, I am totally ignorant...
and might even prefer to stay that way.
CM

Not likely as the military loads 77 grain Sierra boattails in some of its ammo. Besides the heavier bullet will be propelled slower reducing the spin rate.

There used to be a .22/.257 wildat made by someone in California's central valley was was designed for heavy bullets at high velocity. I can't remember the name. I saw some 80+ grain commercial bullets (Hornady?) made and labeled for for it. It must have worked.

Bullshop
12-12-2007, 04:37 PM
BAGTIC
That would be Keneth Clark, and the cartridge was the 224 Clark. It was based on the 257 roberts imp. case. I built one with a 1/9" twist and a 30" barrel that easily did 4100 fps with the then new Siera 69gn bthp match.
BIC/BS

BD
12-12-2007, 05:48 PM
224 Clark, (.22/257); 220 Howell, (22/30'06) and the 223 Vais, (22/6.5x55), were all designed around the idea of high SD .22 bullets moving along at a pretty good clip. The ones I've seen all worked pretty well with an 8 or 9 twist. The 77 grain Sierra or Nosler BTHPs shoot very well out of my 8 twist DCM, as do the 80 grainers if I load'em one at a time. I say the idea of "commercial" bullets flying to bits in "military" barrels is bunk.

And if Bullshop's had the 69 grain Sierras over 4,000 in a 9 twist, then I have to assume that the jacket construction is playing a significant role in addition to rpms, as I have watched 40 grainers dissappear in similar circumstances.

BD