Asymmetric and Unbalanced Bullets

[colt 357]

Dont know if this video has been posted but found it to be very interesting. This guy is shooting bullets that he filed to be off balanced then shot them on high speed camera. Makes me wonder if I am being to picking when inspecting my cast bullets your thoughts guys looking forward to what you guys think about this.

https://www.youtube.com/watch?v=C9Dylxy3zJc

[btroj]

To see the bullet corkscrew in flight tells you much.

[triggerhappy243]

I watched the video and my question to you would be how bad are your cast bullets and secondly what are your intentions for your cast bullets? I shoot cast because besides the propane and my lead, all else was free. i shoot just plinking. so they are not intended for match accuracy at this time. still have not tried accuracy tests. all in good time.

[pretzelxx]

I like how he got the flat to curve upward, that was cool to see

[Larry Gibson]

To see the bullet corkscrew in flight tells you much.

Too bad the pundits of the RPM threshold don't watch this and understand what the helical arc in flight is (the "corkscrew"). They also might take note of how imbalances adversely affect the bullet in flight. The .22LR rounds used had a low RPM to begin with. The RPM threshold was lowered by the severe unbalancing of the bullets so even at that low level of RPM the effect is dramatic. Imagine the increase in RPM if we double the velocity and deacrease the twist from 1-16 (maybe 14") in the test rifle to 10" twist or faster?

Larry Gibson

[rhead]

While it is in the barrel the bullet is forced to spin around the center of the bore. Once it leaves the barrel it will begin to try to spin about its center of mass.

A cast boolit cools and becomes solid from the outside in so there will be an area of lower density somewhere near the center of the boolit. the closer to the center this area is the more accurate the boolit will shoot.

Does a boolit cast from a single cavity mould show more accuracy than a boolit cast from a double cavity mould? I do not own a both single and double cavity mould of the same boolit and probably cannot shoot well enough to see the difference. This is conjecture. has anyone ever tested this. Some of the skilled match shooters should know if (on average) do single cavity moulds preform better than double cavity moulds (which should cool faster from the sides than they do to the end).
If the area of lower density was on the outside the upset should be multiplied.

[Garyshome]

Great video!

[JimA]

Surprising accuracy for some of those bullets. The flat "curveball" was cool.

[Wayne Smith]

Dr. Mann did much more. Damage the base and see what happens! Or read his book, The Bullet's Flight.

[jonp]

Too bad the pundits of the RPM threshold don't watch this and understand what the helical arc in flight is (the "corkscrew"). They also might take note of how imbalances adversely affect the bullet in flight. The .22LR rounds used had a low RPM to begin with. The RPM threshold was lowered by the severe unbalancing of the bullets so even at that low level of RPM the effect is dramatic. Imagine the increase in RPM if we double the velocity and deacrease the twist from 1-16 (maybe 14") in the test rifle to 10" twist or faster?

Larry Gibson

My first thought was the relationship between the off balance corkscrew and rpm of the projectile. Larry, in assuming the RPM is low are you making a general statement about the velocity and an average barrel twist for a 22 rifle? Also, that the rpm will always be lowered by the aerodynamics of the projectile due to drag?

rhead: "A cast boolit cools and becomes solid from the outside in so there will be an area of lower density somewhere near the center of the boolit"

Can you explain this a little more rhead without getting too technical? Do you mean that your melt is of uneven density and the most dense lead migrates naturally towards the outside? Considering how quickly the boolit cools into a solid state the chance of the melt to become uneven in cooling is very small and it will not change much. Hardness and Density are not the same thing. Are you using slang to make a point about how a boolit reacts?

[45 2.1]

Too bad the pundits of the RPM threshold don't watch this and understand what the helical arc in flight is (the "corkscrew"). They also might take note of how imbalances adversely affect the bullet in flight.

This is actually funny, coming from you. We have observed... We do know what is happening... We also know how to cure that problem and have done so.

Here is how:
1. We reduce tolerance stack.
2. We do not shoot substandard dimensioned boolits, especially ones you use.
3. We pay no attention to the use of any 4895 powder or dacron.
4. We use a properly proportioned alloy suitable for the pressures involved.
5. We shoot boolits that actually fit the firearm that aren't undersized.
6. We load them to the required pressure level so they shoot properly.
7. etc.

All the effects you've noted occur with match jacketed bullets also.... and some of them shoot very tiny groups at long range, just like a good boolit does. You might want to look at a BP match grade boolit in flight from muzzle out to about 600 yards and see what it does, you might learn something there.

[C. Latch]

Could someone fill me in on the nature of the RPM threshold feud?

I'm kinda new and must have missed the roots of this one.

[45 2.1]

Could someone fill me in on the nature of the RPM threshold feud?

I'm kinda new and must have missed the roots of this one.

It is fairly old now.... and I'm sure that someone will say something else about it. The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore). He has proposed you can "push" it if you have your ducks in a row OR you can use a slow twist barrel to alleviate it somewhat. While the second is true (and reduces the firearms use for other things), the first is just a wrong assumption caused by other tolerancing factors which have been brought up several times by me and others. Now, lets see if this is succinct enough.

[C. Latch]

It is fairly old now.... and I'm sure that someone will say something else about it. The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore). He has proposed you can "push" it if you have your ducks in a row OR you can use a slow twist barrel to alleviate it somewhat. While the second is true (and reduces the firearms use for other things), the first is just a wrong assumption caused by other tolerancing factors which have been brought up several times by me and others. Now, lets see if this is succinct enough.


Thanks for the explanation. I keep seeing this pop up in various threads (some new, some older ones that I find in searches) and couldn't figure out what the big fuss was about.

[jmort]

I too was surprised by how accurate the " unbalanced" bullets were and that the uneven flat cut was "worse" than the others.

[Larry Gibson]

It is fairly old now.... and I'm sure that someone will say something else about it. The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore). He has proposed you can "push" it if you have your ducks in a row OR you can use a slow twist barrel to alleviate it somewhat. While the second is true (and reduces the firearms use for other things), the first is just a wrong assumption caused by other tolerancing factors which have been brought up several times by me and others. Now, lets see if this is succinct enough.

C.R. Latch

45 2.1's explanation is wrong which is why there is a continuing "feud" as such. 45 2.1 just doesn’t understand that when he says; “The crux of the matter is that the poser of the theory says you will have trouble with unbalanced boolits above a certain RPM (which can be true if you use substandard equipment toleranced incorrectly and you make some decisions so the boolit has plenty of room to get booted out of line with the bore)" that it is absolutely true for 90+ % of rifle bullet casters and shooters. As long as they use regular cast bullets of regular ternary alloys loaded with standard equipment using standard loading procedures their loads will bump into the RPM threshold, generally in the 120,000 to 140,000 RPM range. So when one of those 90%+ ask why they lose accuracy at a certain velocity I explain it to them. The explanation is correct as it pertains to their load. 45 2.1 goes into a nut roll and says it isn't so......problem is he has just admitted it is so. The RPM threshold does exist. He, simply by what he says as we've seen no groups or even photo's of proof of his posted, apparently is adept at pushing the RPM threshold upward. He uses all of the techniques I have stated are necessary for many years on this forum. I assume he is successful as I am but he adamently refuses to demonstrate such to many of us. None the less let us continue.

A simplified definition of the RPM threshold is; “The RPM threshold is that point where accuracy begins to deteriorate when the RPM is sufficient to act on imbalances in the bullet in flight to the extent the bullet begins a helical arc in flight or it’s flight path goes off on a tangent. It is best noted when working up a load as velocity increases flyers begin to happen. Then as velocity is further increased the total group size increases sometimes to the point some bullets fly so far off they miss the target. A further indication the cast bullets at or over the RPM threshold is (or some of them in a load that is on the edge of the RPM threshold) the non linear dispersion of the group size as range increases.” A more detailed explanation is found in the sticky; http://castboolits.gunloads.com/showthread.php?208186-RPM-Threshold-barrel-twist-velocity-chart

45 2.1 continually post untruths about what he thinks I believe and say. So let’s take a look at what his untruths are in this thread as he posted them. I will tell you what I really think and say in answer to each of his "talking points".

1. We reduce tolerance stack.

Unknown what he means by this(?) but assuming he means consistency of loading procedures and equipment so the bullet, cartridge and components along with the rifle are consistent and aligned. Truth is I consistently provide real information as to all this. If one is to push the RPM threshold up then tolerances of the bullet, the cases, the components and the rifle must be as close as we can make them. With factory and milsurp rifles we are pretty much stuck with the way they are assembled as far as tolerances. With custom rifles we are not and can make them to as close as tolerance as possible. With custom rifles we can also pick a rifling twist more conducive to keeping the RPM under the RPM threshold to begin with for cast bullet use at higher velocity.

2. We do not shoot substandard dimensioned boolits, especially ones you use.

45 2.1 continues to offer this untruth. I do not use “substandard dimensioned bullets”. I used a standard 311291 in one test to prove a point. The point was proven. That mould does not produce a nose diameter that “fits” most .30cal bores. Thus 45 2.1 continually used that example of my “substandard dimension bullets” even though I used it intentionally. He ignores the fact that I go to great lengths to ensure proper fit of the bullet to the case neck, the throat and the bore. He ignores I advise to keep the bullet concentric to the bore. He ignores the fact I consistently say if the RPM threshold is to be pushed up a bullet of proper design is needed. Then worst of all he ignores that I use several of his own designed bullets to push the RPM threshold up. Ponder his; if I am using "substandard dimensioned bullets" (I always give the sizing I use in my test reports) then how is it I shot a sub moa 10 shot group at 100 yards at 2600+ fps with a 311466?

I also posted photo’s of 6.5 Kurtz bullet (his design) that were sent to me by a person we can not mention here. The photo and post were deleted by a moderator. These 6.5 Kurtz bullets were sent to me to test by the unmentionable. 45 2.1 posted numerous times of the marvelous accuracy these bullets produced at very high velocity/RPM when shot by the unmentionable. Most of those bullets were rejects by my standards of properly dimensioned cast bullets. They shot very poorly BTW. Thus it is obvious that 45 2.1 and I do have a very different idea of what “substandard dimensioned bullets” really are.

In order to push the RPM threshold up your cast bullets of a ternary alloy must be of consistent dimension and consistent weight. They must fit the case neck, the throat and the bore. They must be loaded concentric to the bore. That is the truth.

3. We pay no attention to the use of any 4895 powder or dacron.

What this has to do with pushing the RPM threshold up is anyones guess? The truth is I almost always recommend a slower burning powder for use in pushing the RPM threshold. Most often I recommend the use of AA4350, RL19, H4831SC and RL22. Those all meter well and they ignite and burn efficiently at lower psi’s of 28,000 to 40,000+ psi’s. They offer a slower time/pressure curve to lesson the unbalancing of the cast bullet during acceleration. I measure the actual pressure and see the time/pressure curve of numerous cartridges in 30+ firearms BTW. All of the powders I recommend most often have an 80%+ load density and do not need a dacron filler nor do I recommend one for those powders with loads that are pushing the RPM threshold.

My recommendation of 4895 powder and the use of a dacron filler has nothing to do with pushing the PM threshold. The truth is; the recommended use by me of 4895 with a dacron filler has to do with standard loads under the RPM threshold. The dacron filler simply holds the owder in position against the primer consistently allowing for consistent ignition and burning of the powder at the lower psi's (usually under 28,000)reducing the extreme velocity spread of the load. That most often simply improves accuracy below the RPM threshold.

4. We use a properly proportioned alloy suitable for the pressures involved.

Yes we do. As mentioned by me in almost any thread of this topic the RPM threshold can be pushed up or down by hardening the cast bullet through heat treating or annealing and change in alloy by hardening or softening with the addition of additional lead or copper for example. If you want to push the RPM threshold up then hardening the bullet is needed. I use a heat treated ternary alloy and BadgerEdd’s copper alloy for the highest velocity/RPM loads. Though I have pushed the 311466 of ternary AC’d alloy to 2600 fps with sub 2 moa accuracy out of my 14” twist Palma rifle and to 2400+ fps out of my 12” twist M70 Target rifle. Out of my 10” twist pressure test rifle accuracy goes over 2 moa at 2100 fps. Those are all .308Ws and the tests are with 10 shot groups at 100 yards.

With the hardened alloys I am pushing 2750 fps with 2 moa accuracy using the 311465. I also shoot the MP 311-180 (one of 45 2.1s designs) to the full potential of the .308W in both the 12 and 14” twist rifles at 2400+ fps.

5. We shoot boolits that actually fit the firearm that aren't undersized.

45 2.1 sure is stuck on that one, eh?

6. We load them to the required pressure level so they shoot properly.

As do I and anyone else who pushes the RPM threshold. The “required” pressure level is needed for efficient burning of any powder. All powders have a “required pressure level” before they burn efficiently. The faster burning powders burn efficiently with as low as 7 - 8,000 psi and the slowest require upwards of 40,000+ psi to burn efficiently. The trick is to use the right slower burning powder that gives 80%+ load density, that burns efficiently and that gives the slowest time/pressure curve to push the RPM threshold up.

7. etc.

Looks like 45 2.1 ran out of untruths and has already repeated the “fit” one………it is unfortunate 45 2.1 doesn't pay close attention to what he said in this thread (I posted it in this post above) as he does actually agree with me. However, he made his bed and is insistent on sleeping in it I guess.......thus the "feud".

So C.R. Latch I would invite you, if you are interested, to look at what I’ve posted here and really posted on the other threads relating to the RPM threshold. Look at the tests I’ve done, the target groups I’ve posted and my willingness to demonstrate such by going shooting with you, 45 2.1 or anyone else. If you shoot cast bullets in rifles and have worked up a load and found the accuracy went south at a certain velocity simply convert that velocity to RPM and you will find the RPM threshold.

Larry Gibson

[Idz]

So how much of the corkscrew is caused by the off center weight and how much is due to the totally screwed up aerodynamics? Did Mann separate the effects by drilling out an off-center core of lead and then plugging it with plastic or something?

[mrbill2]

Well C. Latch now you went and done it. You had to stir the pot, didn't you. Here we go again. Which came first, the chicken or the egg? :kidding:

[C. Latch]

I certainly learned a bit today.

In all seriousness, my interest in this would be academic, not practical; unless I get a wild hair to shoot my '06 a lot and start stuffing my 30-30 boolits into it, I'll probably never launch a cast projectile faster than 2000' to 2200' MV. Right now most of my shooting is .45 Colt and .45 ACP. That's not to say that the argument above isn't worthy - physics is fascinating stuff and well worth learning - it's just, honestly, more than I can chew on at the moment.

[45 2.1]

Well C. Latch now you went and done it. You had to stir the pot, didn't you. Here we go again. Which came first, the chicken or the egg? :kidding:

Awww, mrbill2....... Larry sure does go on a tear on those long posts trying to convince folks he is right. He has done the same thing on more than one forum about that video and gotten his backside handed to him, some of it by people from here. I think C. Latch and others can make up their own minds about this nonsense from what is written here.

[fouronesix]

There is good info in that video! Thanks for posting.

Interesting given the Aussie hare shooting thread (elsewhere on this forum) about ineffective 22 RF ammo. Also in another thread, some posts suggesting cutting the front of the bullet off for more "whack". I posted that I had tried it with a 22 RF as a youngster many moons ago and found no difference in "killing" effectiveness on small game plus poor accuracy. The flight path of that 90 degree cutoff 22 bullet in the video reinforces what I noticed on target all those years ago. I feel vindicated!

[Larry Gibson]

C.R. Latch

You may or may not be running up against the RPM Threshold with your '06 loads, depends on several factors at the level of your loads. Sounds like you're loading them well enough though. Nothing to consider with the 45 Colt loads unless you use to soft an alloy. Don't worry about the "feud", most don't take our bantering seriously.

I've ask 45 2.1 numerous times to find at least one forum member out here he trusts to come see me cast, check on the quality of my bullets and loads and watch me shoot them or shoot them themselves. I offer that because he won't shoot with me. I'm open to any forum member wanting to shoot with me and see proof of the RPM Threshold and actual accuracy at 2500-2600+ fps. We can even use 45 2.1s excellently designed 311-180 gr bullets in 10, 12 & 14" twist rifles to prove the RPM Threshold. Be more than happy to accommodate any forum member.

Larry Gibson

[45 2.1]

Give it a rest Larry........... very few people care or are interested.

[Walter Laich]

I was impressed how straight they flew. Wonder what kind of camera and did he paint base a light color so we could see it better?

[Larry Gibson]

What 45 2.1.......you obviously are "interested"........you keep posting.

The offer is made to settle the issue. Find someone to shoot with me and observe since you won't. If I prove the point you keep quiet. If I can't prove the point I keep quiet. How about that?

Larry Gibson

[C. Latch]

Larry,

My username is C. Latch.

You're referring to me as C.R. Latch.

How do I know you? Nobody on this forum knows my middle name or initial, that I know of...except you, apparently.....:wink:

[Scharfschuetze]

An interesting video to say the least and fun to watch. It would be interesting to compare a 5 or 10 shot group of undamaged ammo to a group fired with similarly damaged bullets out of the same rifle at the same range.

The helical flight path of the projectiles reminds me of when we converted from the M16A1 rifle to the M16A2 back in the mid eighties. For some time, we had both versions of the rifles available to us and we often shot the older 56 grain ammo (M193) in the new M16A2 rifle with its much faster 1 in 7" twist rifling. Several lots of this ammo would at times barely hold an E Type Silhouette (40" x 20") target at 300 yards. Those lots of M193 ammo, while quite accurate in the older M16A1's 1 in 12" twist rifling, were apparently getting over stabilized in the M16A2. I guess you could say they hit or surpassed their "RPM threshold" and their grouping ability went south. Good lots of M193 ammo would shoot fairly well in the 1 in 7" twist and we could only assume that their balance and concentricity was much better than the average lots of M193 that were spun right off of the target at times.

Conversely, the longer and heavier M855 green tip ammo for the M16A2 when fired in the M16A1 rifle would not stabilize and would start to key hole as close as 25 yards. The 1 in 12" twist would not rotate the projectile fast enough for its length. I guess it was RPM challenged and way below the rotational threshold required for stability and accurate shooting.

An interesting aside to this conversation again is based on the two rifling pitches of the M16/M4 series of weapons. At one time we could draw .22LR sub cal kits from TASC for our service rifles. When we used the army white box match .22LR Standard Velocity ammo in our M16A1s with their slower twist, we could easily qualify on the Alternate "C" qualification target at 25 yards. When we used the sub cal kits with the M16A2, we once again had issues with poor grouping and often could not stay on the scaled 250 and 300 yard silhouettes. I'll bet with high speed photography, we would have see the helical flight path shown in the video in the original post. With the M16A2s and their 1 in 7" pitch (over twice as fast as a purpose made .22RF pitch) I'm sure that we would have demonstrated that the swaged 40 grain .22 bullets had passed their RPM threshold and were spinning too fast for accuracy. Within a few years of the adoption of the M16A2, the sub cal kits vanished and were no longer available. I guess we weren't the only troopers having trouble withe the kit and the M16A2.

The take away for me at the time is that specific rifling twists will stabilize specific weights of projectiles and when you use a twist faster or slower than the projectile it's designed for or a too high or low a velocity for the pitch you may run into accuracy problems.

[KYCaster]

I too was surprised by how accurate the " unbalanced" bullets were and that the uneven flat cut was "worse" than the others.



I get an entirely different message from the demonstration. Only two of the altered bullets would have been a killing shot on any creature I'd hunt with a .22RF. (groundhog or smaller) So I consider accuracy effectively ruined.

YMMV
Jerry

[Larry Gibson]

Larry,

My username is C. Latch.

You're referring to me as C.R. Latch.

How do I know you? Nobody on this forum knows my middle name or initial, that I know of...except you, apparently.....:wink:

C. Latch

My opologies, perhaps it just "sang":drinks:

Larry Gibson

[TXGunNut]

That's not to say that the argument above isn't worthy - physics is fascinating stuff and well worth learning - it's just, honestly, more than I can chew on at the moment. -C. Latch

I understand that all too well. I read the RPM Threshold sticky soon after I joined here, read several posts about it but didn't truly understand it until I encountered it and measured it with my boolits, loads and guns. Much can be learned from both sides of this issue because as Larry points out they aren't actually that far apart. OTOH both 45 2.1 and Larry have forgotten more about what it takes to make a cast boolit work than I'm ever likely to know so I enjoy the spirited debate, I learn a little more each time.

[rsrocket1]

I wonder if the helical paths are caused more from aerodynamic imbalance than they were from weight imbalance. The one bullet with the bite taken out of the middle (nose still in good shape @2:51) looked like it flew pretty straight despite having a severe weight imbalance.

[C. Latch]

C. Latch

My opologies, perhaps it just "sang":drinks:

Larry Gibson

LOL. No apology needed. Just made me wonder who was watching me. [smilie=1:

[Scharfschuetze]

"I wonder if the helical paths are caused more from aerodynamic imbalance than they were from weight imbalance."

Tracers, which can burn a bit inconsistently, are not usually considered as accurate as ball ammo; although they are designed to mimic the trajectory or ballistics of the ball ammo in their calibre. Part of that reason is the burning phosphorus in the base of the projectile continually changes the weight and concentricity of the projectile. This takes place while the rest of the bullet remains uniform in shape, unlike the purposely damaged ogives in the video. So while these are well within their design parameters, they also tend to misbehave to some extent like the purposely damaged .22s in the video. Perhaps not germane to the thread per se, but interesting none the less when discussing stability, over stability or lack of stability.

One can see a helical tracer bullet path in many WWII footage of air to air or air to ground engagements, particularly of German 8mm tracer projectiles.

[KYCaster]

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

For the mathematicians and engineers among us. You can probably understand it much better than I can.
Jerry

[rhead]

I wonder if the helical paths are caused more from aerodynamic imbalance than they were from weight imbalance. The one bullet with the bite taken out of the middle (nose still in good shape @2:51) looked like it flew pretty straight despite having a severe weight imbalance.

I would say yes since anything that would be likely to cause an aerodynamic imbalance would also cause a weight imbalance. the effect would be additive. If there was a flaw on the boolit that would cause both increased drag and a weight imbalance the corkscrew effect could be dramatic. Think of one groove being half again as deep as the others. Fortunately many of the flaws that will cause aerodynamic instability can be spotted by inspecting the boolit before loading or will be corrected by the trip down the barrel. (.002 oversize shoots better than .001 oversize??)

[rhead]

My first thought was the relationship between the off balance corkscrew and rpm of the projectile. Larry, in assuming the RPM is low are you making a general statement about the velocity and an average barrel twist for a 22 rifle? Also, that the rpm will always be lowered by the aerodynamics of the projectile due to drag?

rhead: "A cast boolit cools and becomes solid from the outside in so there will be an area of lower density somewhere near the center of the boolit"

Can you explain this a little more rhead without getting too technical? Do you mean that your melt is of uneven density and the most dense lead migrates naturally towards the outside? Considering how quickly the boolit cools into a solid state the chance of the melt to become uneven in cooling is very small and it will not change much. Hardness and Density are not the same thing. Are you using slang to make a point about how a boolit reacts?

I will try. First the more pure lead will migrate to the outside but that is because of its melting point not the cooling rate. what you are describing is a single pass in a zone melting purification process. Describing that in detail would take pages and the differences in alloy composition after one pass would not be detectable after one pass (but the difference is real as the evidence or making ten thousand or a hundred thousand passes shows.

What i was trying to say is that since the melted alloy decreases in volume as it cools (Note the dimple that forms on the top of an undersized sprue). Pouring an oversize sprue will minimize the effect just like pouring with a hotter mould will but is there any way to make it go away completely?

1: The cavity of the mould is filled and overfilled with alloy that is well above its melting point.

2: the mould and the alloy begin to cool from the outside of the mould. the total volume of what was poured will decrease pulling melted alloy down into the mould.

3: Once the hole in the sprue plate becomes solid it can no longer draw more alloy from the sprue but there is still some liquid allow in the interior of the boolit as it cools and becomes solid it will occupy less space than it did as a liquid. The distance between the micro crystals will become greater.

4: IF one side of the mould cools slower due to another cavity filled with molten allow a few tenths of an inch away this area would not be at the center of the casting.

As I stated earlier due to old age and a lack of talent I cannot detect a difference. My question was to some of the ones on the board who can shoot very well. Can they detect a difference in group size in a single cavity mould and a double cavity mould. the interior of the casting should be both less dense and less hard. I don't know of a way to measure either without work hardening the metal.

I hope I hope I helped instead of confused further.

[alfloyd]

"Which came first, the chicken or the egg?"

The chicken.

Lafaun

[dverna]

Larry.

Thanks for the post. I realize it is a bone of contention between the two camps but much of what you explain makes sense. In the end, we need to try to understand why things happen so that we can determine how to develop accurate loads.

On the video, I found it pretty useless. Yep, deformed bullets are not accurate. Never would have guessed.

Don Verna

[geargnasher]

In the end, we need to try to understand why things happen so that we can determine how to develop accurate loads.
Don Verna

If we want accuracy, we need to understand what's going on. One can band-aid the real problem and get mediocre to decent results, or one can ascertain and correct the problem and get excellent results. To do the latter, gaining a deeper understanding of the "tolerance stacking" mentioned by 45 2.1 is a good place to start, but it is only a start.

It IS rather obvious that deformed boolits don't fly straight, one can fix the deformation or slow the rotation to where such deformation has less effect. Or one can do both.

Gear

[Larry Gibson]

Gear is correct. Keeping tolerances "stacked" correctly will give give some push to the RPM Threshold. Doing both by stacking and slowing the RPM with a slower twist will achieve accuracy at a much higher level of RPM.

Larry Gibson

[dverna]

I have always assumed that the reason we can not achieve the same accuracy with cast (or at least it takes a lot more effort) is that cast bullets are inherently less consistent. There may be small voids, molds may not always close the same way, pouring consistency can cause differentials in fill, mold temperature changes (caused when the cadence is interrupted) affect fill,, alloy may be slightly different just after fluxing than after 50 pours etc etc.

If I understand the RPM theory, it essentially states, that there is a point where some "normal" variation in the bullet causes the bullet to become more unstable than acceptable. The bullet has always been unstable but stable enough to provide reasonable accuracy when velocity (spin rate) was behold this threshold. One this point is reached, the bullet must be "more perfect" - and/or it needs to be loaded with more consideration to the kinds of things we do for benchrest ammo- and/or the gun itself must be better (chamber consistency?)

We go ga-ga over a 3/4" cast group that would be relatively easy to accomplish with jacketed bullets in a hunting rifle. We know that something like a .35 Remington is more "cast friendly" (= less affected by bullet inconsistency) than a 5.56.

The loading techniques that allow us to achieve good accuracy with the more perfect jacketed bullets are not good enough to address the variations that occur in a cast bullet. So, we need to take more care to things like neck tension, bullet concentricity, bullet distance to the lands, etc etc.

This "threshold" will move upwards as we either load better bullets or improve how we manufacture the ammunition.

What I am not sure of - but suspect - is there could be a "harmonic zone". Much like a tire that is out of balance. It runs fine at less than 40 mph (even though out of balance), but shakes excessively at 50-60 mph, yet seems to run better again at 75 mph. When we develop a load we start from the sub 40 mph area and things start to go to hell as we get to the harmonic zone - so we improve the balance of the bullet/load. But we either do not or can not drive the bullet past this harmonic zone. Or it could be the imbalance is so destructive, the bullet can never fly true at any speed past X.

Cabin fever is a funny thing.

Don Verna

[Digital Dan]

Wish there was some way I could snap my fingers and the rank and file instantly understood the mechanics of spin stability and all the baggage that goes with it. It is quite clear that many don't.

[45 2.1]

45 2.1 continually post untruths about what he thinks I believe and say. So let’s take a look at what his untruths are in this thread as he posted them. I will tell you what I really think and say in answer to each of his "talking points".

1. We reduce tolerance stack.

Unknown what he means by this(?) but assuming he means consistency of loading procedures and equipment so the bullet, cartridge and components along with the rifle are consistent and aligned. Larry Gibson


Gear is correct. Keeping tolerances "stacked" correctly will give give some push to the RPM Threshold. Doing both by stacking and slowing the RPM with a slower twist will achieve accuracy at a much higher level of RPM. Larry Gibson

Wow... talk about using new terms and NOT understanding anything about them. I read these and now I have to clean my monitor and keyboard. Don't drink anything while reading things here, it's a lot safer that way.


If we want accuracy, we need to understand what's going on. One can band-aid the real problem and get mediocre to decent results, or one can ascertain and correct the problem and get excellent results. To do the latter, gaining a deeper understanding of the "tolerance stacking" mentioned by 45 2.1 is a good place to start, but it is only a start. Gear

Ha, you were paying attention...............


I have always assumed that the reason we can not achieve the same accuracy with cast (or at least it takes a lot more effort) is that cast bullets are inherently less consistent. There may be small voids, molds may not always close the same way, pouring consistency can cause differentials in fill, mold temperature changes (caused when the cadence is interrupted) affect fill,, alloy may be slightly different just after fluxing than after 50 pours etc etc. Don Verna

What actually goes on isn't talked about here too much. It ISN'T what is written about either by the vast majority of people here.

[Larry Gibson]

Gentlemen

The RPM threshold has nothing to do with the spin stability of the bullet. It has to do with the effect of the centrafugal force on the imbalances in the bullet during flight. All the discussion on spin stabilization, yaw, pitch and "going to sleep" are completely different aspects. The RPM threshold and what occurs has nothing to do with those.

BTW; if the unbalanced tire was not physically held on to the axle (what it rotates around) it would go bouncing off in some direction. The higher the tires RPM the bigger the bounce would be. The bullet above the RPM threshld is not physically held onto the axis of flight (what it rotates around) and does go off on a tangent or helical arc. The higher the RPM the larger the departure from the axis of flight. It is cantrafugal force acting on imbalances in the tire and bullet that cause both.

Larry Gibson

[45 2.1]

Gentlemen

The RPM threshold has nothing to do with the spin stability of the bullet. It has to do with the effect of the centrafugal force on the imbalances in the bullet during flight. All the discussion on spin stabilization, yaw, pitch and "going to sleep" are completely different aspects. The RPM threshold and what occurs has nothing to do with those.

BTW; if the unbalanced tire was not physically held on to the axle (what it rotates around) it would go bouncing off in some direction. The higher the tires RPM the bigger the bounce would be. The bullet above the RPM threshld is not physically held onto the axis of flight (what it rotates around) and does go off on a tangent or helical arc. The higher the RPM the larger the departure from the axis of flight. It is cantrafugal force acting on imbalances in the tire and bullet that cause both.

Larry Gibson

I believe the correct term is "Centrifugal" you are trying to say, after using two different incorrect versions. It always helps credibility if you can spell the term used or name of the person you're quoting from a book (or not), the proper use of the word and what is actually does.

[Digital Dan]

Williston, Florida — According to Williston Police, a wheel broke free from a car and killed an man early this Monday morning, March 2, 2014.

Police said that it was first believed that a tire compressor had exploded and killed the man, but that later proved to be false.

Investigations revealed that Patrick Woodard of Gainesville was driving north on U.S. 41 in a 1999 Toyota at around 9 a.m. As the vehicle approached the Absolute Auto Body shop at 104 NW 10th Avenue, the left front tire broke free from his car and flew north on the west shoulder of the highway.

The tire then hit a driveway apron with such force, it became airborne. It then cleared a 6-foot-tall metal fence and struck Ivan J. Sandquist, 33, of Williston, killing him instantly, according to police.

After striking Sandquist the tire then hit James E. Fender, 45, of Williston. He was airlifted to UF Health Shands Hospital with serious injuries, according to reports..

Williston Police said they were assisted at the scene by the Levy County Sheriff’s Office crime scene unit and the Florida Highway Patrol.

Police said the investigation into the accident is still ongoing at this time, and they do not have a cause as to why the wheel broke free from the moving car.

[popper]

A similar examination shows that the Magnus force has a destabilizing effect and increases the yaw angle, if its center of pressure is located in front of the CG. Later, this observation will become very important, as we will meet a dynamically unstable bullet, the instability of which is caused by this effect.
Someone in another thread made a comment that we need a tail heavy boolit for accuracy & stability. The quote above is the correct solution. Note the damaged nose bullets will form a helix then take off tangentially. As Larry has tried to state many times, the centripetal/centrifugal forces and strength of the boolit above an RPM value increases the yaw angle and increases the helix orbit. The spin (RPM) and imbalance generate the Magnus force. Directly related to gyro precession. Magnus forces get really nasty in the transonic range.

[Larry Gibson]

Thanks popper. I'm on the road and mostly answer such posts using my "smart" phone which auto corrects what "it" thinks is the word I want to use. Sometime my thumbs mispell words on the small keyboard. Apparently 45 2.1s point is if I mispell a word I don't know what I'm talking about and there for because of a mispelled word the facts are changed. Suppose that's the best he can come up with though. Fact is it is the centripetal/centrifugal force acting on the imbalances that generate the Magnus force just as you say. That I used/mispelled or my phone selected the wrong word does not change the truth of what is occuring no matter how much 45 2.1 wishes it would. Thanks again.

Larry Gibson

[Digital Dan]

As I said, "the baggage that goes with it".

I rather prefer thoughtful inquiry and discussion to sniping minutiae.

Good post Popper, thank you. There's no end to the benefit of rifled barrels, or the evil, if one is a pessimist at heart.

I'm pondering a few odds and ends along the lines of this OP, but my mind has no guard rails. Deforming bullet noses does what it does to illustrate the extreme, but the more profound effect(s) are generated by imbalance about the outer circumference of a bullet. This is so because at a given RPM and due to a greater radius, the effect is more energetic. It does not do to simply file a chunk off the base to demonstrate this because the analysis is confused with the effects of asymmetric pressure (and resulting flow field disruption) on the base as it exits the muzzle.

On another tangent, since this conversation seems to roll that way, it has been commented on several times in recent months that paper patch bullets do not seem to be so subject to these effects until perhaps a higher velocity is achieved? One one part I get it, that being the circumstance where swagged lead bullets are used. Be they lead or jacketed bullets, when they come out of a swage die they are as perfect as machine tools and the dies they make can produce. I differentiate swagged bullets from cast in the context of patched bullets squeaking by the more normal threshold of chaos associated with cast bullets. Anyone have any observations on one or the other?

I have seen some projectiles do some very odd things in my day. One of the easiest ways to see such things is to fire a lot of bullets under different lighting conditions with different and contrasting backdrops. An example would be a minigun being fired with sunlight behind the shooter, toward a cloud shadowed and vegetated hillside. Glimmer is far better for visual observation of a bullet's flight than anything I've seen.

[45 2.1]

The thing to remember here is............. these forces act a lot more on boolits that are tipped to the centerline of the bore when they exit. Whether it is tipped or not is YOUR fault. You loaded the cartridges for your rifle. Make good choices and have the centerline of the boolit in line with the centerline of the bore when it exits and those forces will have very little effect on what your results are.

[geargnasher]

I'm not big on posting photos of high-velocity groups, but this should illustrate 45 2.1's point very well. These two groups were fired from a box-stock Savage 111 Pig Gun in .308 Winchester, 1-in-10" twist, 20" barrel, from bags on a good bench, 100-yard range, at a chronographed 2,347 fps average. Those are 1" pasties. The alloy is water-quenched 50/50 wheel weights and lead soil-stack boots, plus 1% total additional tin. Nothing more than traditional grease-groove lube and Hornady gas checks were used.

While these are not really bragging groups in many circles, and there is considerable room for improvement (the lube, for one thing), I don't believe there are many people here who could match them in such a rifle.

BTW, just for fun I did another experiment with more "mainstream" techniques used by most cast boolit shooters, and with a center aim point got seven out of 10 to strike somewhere on one of the 8-3/4x11-1/2" work order hard cards that I use for most of my targets using the same boolit and powder charge. The difference? All achieved with the way I crafted the ammunition, nothing else.

Gear

ETA I snapped the pic tonight for this post, the groups were fired earlier this year.

[fouronesix]

Oh my, not another rpm threshold debate!

Back to the OP. I think many of those 22rfs are probably leaving the muzzle more or less sonic and probably transitioning subsonic on the way to the target. At those modest vels and given the likely twist of the 22 rf bore- I think most of that helical flight behavior is simply a combination of the basic aerodynamic instability of a common conical bullet shape (the average 22 rf bullet) having it's ubiquitous fight with gyroscopic stabilization. That helical pattern may very well be the precessional phenomenon, as has been suggested, exaggerated with both the center of aerodynamic form and center of mass being off-axis.

[Larry Gibson]

Gear

I'll be driving right by Kerrville in 3-4 days. How about showing me how you do that? I've the time
and will be right there.

Larry Gibson

[C. Latch]

Someone in another thread made a comment that we need a tail heavy boolit for accuracy & stability.

You may be referring to a post I made the other day in another thread concerning handgun bullets. If so.....exactly where was I wrong?

Apologies if I'm assuming too much here.

[C. Latch]

Wish there was some way I could snap my fingers and the rank and file instantly understood the mechanics of spin stability and all the baggage that goes with it. It is quite clear that many don't.


Explain it and you're guaranteed a sticky thread, albeit it one with fifty pages of arguing.

I'd read it, for sure. I posted a thread the other day asking a stability question and got very little response.

[popper]

fouronesix nailed it.
C. Latch -
Magnus force has a destabilizing effect and increases the yaw angle, if its center of pressure is located in front of the CG. This is a nose heavy config. and is actually the 'drag' configuration.
CG is center of volume. CP (CF) is center of area, for a straight flying boolit. CP moves forward for a yawing boolit. HPing moves CG rearward, no basic change in CP, unless you consider the Paco Kelly 'cup' pressure. I think his approach works in transonic region (22RF).

[DeanWinchester]

Ive got a Keith style SWC 35 cal mold (158g) that I have used in .38 special, .357 mag & 35 remington. It is NOTICEABLY eccentric. The nose is way out from the driving bands. It's right embarrassing to look at. It shoots like a house fire. Out of my 35 remington it groups really well. It's always been a mystery to me, but if it works…...

[C. Latch]

fouronesix nailed it.
C. Latch - This is a nose heavy config. and is actually the 'drag' configuration.
CG is center of volume. CP (CF) is center of area, for a straight flying boolit. CP moves forward for a yawing boolit. HPing moves CG rearward, no basic change in CP, unless you consider the Paco Kelly 'cup' pressure. I think his approach works in transonic region (22RF).

OK, I get all that.....

It still doesn't explain why conventional wisdom (CG behind CP) about spin stabilization is wrong.

[Digital Dan]

With possible exception of double end wad cutters or minie bullets, all conical bullets present CG aft of CP. The larger the displacement between these two centers the faster twist rate must be for a given caliber.

The relationship between gyroscopic stability, bullets and exterior ballistics is a bit difficult to explain in the course of an internet post. There really isn't much there to argue about, the science is clear. The discussion is suitable for books and more than a few have been written.

Modern Exterior Ballistic by Robert McCoy
Rifle Accuracy Facts by Harold Vaughn
Understanding Firearms Ballistics by Robert Rinker

Also, you may take a read or three of Brian Litz online. Some of his work is available via the Sierra web site.

Additional: Dr Mann - The Bullet's Flight, From Powder to Target
General Julian Hatcher - Hatcher's Notebook

[felix]

I do not find ballistics too difficult to understand. Understanding depends upon the teacher's interests as well as that of the receiver's. ... felix

[youngda9]

Gear...have you fired that same load out at 200 yards, or greater, to determine if the group size increases linearly? Those bullets are at 169,000 RPM. Please take Larry up on his offer.

Somehow I doubt you will, and the debate will rage on...

[C. Latch]

I'm going to shamelessly throw a link in here and ask some of y'all to help me:

http://castboolits.gunloads.com/showthread.php?233061-I-have-a-question-related-to-WFN-type-bullets-and-stability-and-CoG

This seems to be the thread where all the physics folks are posting; in hindsight I should have put that thread in this forum, I guess.

[Digital Dan]

I do not find ballistics too difficult to understand. Understanding depends upon the teacher's interests as well as that of the receiver's. ... felix

Once one digests the material it isn't all that bad, but teaching it is another ball of wax. As example, you might understand the tractability condition, but would you care to explain it and the relationship to gyroscopic stability factor(Sg) over the course of 1,000 yards? Please highlight the nature of Sg change resulting from velocity decay and the resultant impact on tractability.

[45 2.1]

Gear...have you fired that same load out at 200 yards, or greater, to determine if the group size increases linearly? Those bullets are at 169,000 RPM. Please take Larry up on his offer.
Somehow I doubt you will, and the debate will rage on...

I can about guarantee your last sentence is correct.

Gear knows about 50% of what it takes to shoot extremely small groups. He is at the point he needs to ask for more. As for groups increasing linearly, they don't.... the MOA figure can lower as range increases when you get all your ducks in a row. It just takes a lot of work to do so and what it actually takes is learning several things which aren't learned in a day or month. Usually it takes 6 to 8 months to teach someone how to go from 1.25 MOA to less than 0.5 MOA. Semi-autos are another item altogether, but they can do the same.

[swheeler]

Colt 357 thanks for the link! That's about what I expected to see, cripers imagine if that 22 had a 10" twist barrel:O

[swheeler]

He'd need a bigger backstop;)

[geargnasher]

The debate will rage on until more people learn how to load accurate cast boolit ammunition. 45 2.1 has revealed the "secret" to doing as well as I do once in this thread yesterday and once in another thread here today. All I have heard is crickets chirping and an occasional insinuation that we are liars. I am not going to spoon-feed any of you and I doubt 45 2.1 is either. No one is going to watch me shoot anything for proof; learn how and prove it to yourselves like I am doing.

This is exactly why I don't post pictures of my groups with velocity details, and why many who CAN do this have either quit the forum or don't discuss it.

Gear

[Digital Dan]

If one crafts perfect ammo and fires it from a perfect rifle with flawless execution...you might wind up like a fellow named Michael Rix at Raton last year. On 9-16-13 during the BP Cartridge Target Rifle Nat. Championships he was firing at the 600 yard line with a Stevens rifle replica chambered in .40-60 Maynard. He used a Paul Jones mould to craft 408 grain bullets which were propelled by 61 grains of 2Fg Swiss powder.

Shots 7-10 of the string grouped at less that 1" spread in the X-ring of a German ring target. From a prone position using cross sticks. The picture of the target is published in the most recent edition of Black Powder Cartridge News.

The question that comes to my mind in the afterglow of this love fest, do I really need to make inroads to high velocity with lead bullets or can I do art work at more modest velocity? I think the latter mostly, but I'm quite certain if I try for the high end and fail, it probably isn't the fault of the bullet I cast or the cartridge I loaded.

No, I think I'll blame it on my Ex.

[45 2.1]

Gear made as succinct a statement as he has EVER made about the situation..... Good Job on that Gear.

As for this statement:
Or can I do art work at more modest velocity? I think the latter mostly, but I'm quite certain if I try for the high end and fail, it probably isn't the fault of the bullet I cast or the cartridge I loaded. No, I think I'll blame it on my Ex.

What one thinks and what one does is usually two different things when actually tried. I think you can really blame it on Gear's crickets if you fail.

[ShooterAZ]

Chirp...

[C. Latch]

If y'all argue this much over physics, I'm never venturing into the politics or religion forums. :grin:

I'd still like someone to explain to me whether or not I'll benefit from hollowpointing a mold that is marginally stable given the velocity, twist, and bullet length/meplat I'm trying to shoot in my .45 Colt. Here's that link again:

http://castboolits.gunloads.com/showthread.php?233061-I-have-a-question-related-to-WFN-type-bullets-and-stability-and-CoG

[geargnasher]

Anything that moves weight to the rear (or removes it from the front) will help a spin-stabilized projectile remain so. The inverse is true of a weight-stabilized projectile, such as a spear, shuttlecock, or shotgun slugs intended for smoothbores.

Gear

[Digital Dan]

Gear made as succinct a statement as he has EVER made about the situation..... Good Job on that Gear.

As for this statement:
Or can I do art work at more modest velocity? I think the latter mostly, but I'm quite certain if I try for the high end and fail, it probably isn't the fault of the bullet I cast or the cartridge I loaded. No, I think I'll blame it on my Ex.

What one thinks and what one does is usually two different things when actually tried. I think you can really blame it on Gear's crickets if you fail.

Sorry, I have no idea what you mean by that.

[Digital Dan]

Anything that moves weight to the rear (or removes it from the front) will help a spin-stabilized projectile remain so.

Gear

Gear, would you mind explaining that for me.

[Larry Gibson]

The debate will rage on until more people learn how to load accurate cast boolit ammunition. 45 2.1 has revealed the "secret" to doing as well as I do once in this thread yesterday and once in another thread here today. All I have heard is crickets chirping and an occasional insinuation that we are liars. I am not going to spoon-feed any of you and I doubt 45 2.1 is either. No one is going to watch me shoot anything for proof; learn how and prove it to yourselves like I am doing.

This is exactly why I don't post pictures of my groups with velocity details, and why many who CAN do this have either quit the forum or don't discuss it.

Gear

That's about the response expected. Since the grandmaster says you're only "50%" there and you self proclaim having "hit a wall" at the RPM threshold would I have learned anything?

However, gear, if you get out Arizona way give me a shout and I'll show you how to get such accuracy (as the target you posted) at 2600+ fps even though I obviously know considerably less than you and none of us know anything compared to grandmaster. But what the hey, some of us are happy with 1 - 2 moa at such velocity with cast bullets. And some of us continue to push the threshold.

do I really need to make inroads to high velocity with lead bullets or can I do art work at more modest velocity?

You certainly can do art work at more modest velocity. But then shouldn't we be happy with a patched RB at 100 yards with such accuracy? Or how about a musket at 25 yards? A bow and arrow? Some of us always push the threshold, just the nature of things. Not to say we aren't also very pleased with accuracy at or under the RPM threshold. Most of my rifles get shot with such loads. That doesn't mean I can also be pleased with pushing the RPM threshold up. It might be a very, very dull forum if we all did the same thing............

"Chirp"

Larry Gibson

[Larry Gibson]

Gear...have you fired that same load out at 200 yards, or greater, to determine if the group size increases linearly? Those bullets are at 169,000 RPM. Please take Larry up on his offer.

Somehow I doubt you will, and the debate will rage on...

youngda9

No "debate" actually as I can and am willing to prove to anyone what I say and that the RPM threshold is real. Gear has already admitted the RPM threshold is real and has come up against it with his 30x57(30 XCB) rifles. Most others have come up against it also. I'd venture you have also if you shoot cast bullets in CF rifles with 12" or faster twist barrels?

Larry Gibson

[6bg6ga]

I watched the video and my question to you would be how bad are your cast bullets and secondly what are your intentions for your cast bullets? I shoot cast because besides the propane and my lead, all else was free. i shoot just plinking. so they are not intended for match accuracy at this time. still have not tried accuracy tests. all in good time.

Thats a good point ...how bad are your bullets? Is it possible to have bullets that are out of balance? Could this out of balance be the cause of fliers? So many questions and a lot of speculations. Some proven and some not.

I seem to obtain my best accuracy buy a very tight selection of cases, weighed bullets out of the same alloy and casting batch and powder charge trickled. This in conjunction with finished rounds measured for equal OAL seems to yeald me very good groups.

[6bg6ga]

A question... can loading cast bullets that are slightly shorter OAL contribute to asymmetric and unbalanced bullets due to the bullets distance from the rifling? Thought being the cartridge is fired the bullet jumps and hits the rifling causing some lead loss and this causes a slight imbalance?

[Digital Dan]

do I really need to make inroads to high velocity with lead bullets or can I do art work at more modest velocity?

You certainly can do art work at more modest velocity. But then shouldn't we be happy with a patched RB at 100 yards with such accuracy? Or how about a musket at 25 yards? A bow and arrow? Some of us always push the threshold, just the nature of things. Not to say we aren't also very pleased with accuracy at or under the RPM threshold. Most of my rifles get shot with such loads. That doesn't mean I can also be pleased with pushing the RPM threshold up. It might be a very, very dull forum if we all did the same thing............

"Chirp"

Larry Gibson

I got one bullet what weighs 850 grains. I really, really, really don't want to push the RPM thing with that. I hope you understand that I'm just an ol' worn out scout and I like by shoulder bones in one piece.

[C. Latch]

Anything that moves weight to the rear (or removes it from the front) will help a spin-stabilized projectile remain so. The inverse is true of a weight-stabilized projectile, such as a spear, shuttlecock, or shotgun slugs intended for smoothbores.

Gear

That is the understanding I've always had.

I don't know if the folks here are declaring it to be completely wrong, or just hinting at some limitations to this as a rule of thumb, but I wish they'd explain themselves. My understanding is that with a typical pointed bullet, shifting the CG rearward (by way of hollowpointing the mold) shifts the CG further towards the center of the bearing surfaces of the bullet, which reduces the impact of irregularities in the portion of the bullet outside of the bearing surfaces.

Again, I'll freely admit that I'm not a physicist, but would be happy to learn - just not interested in reading an entire book just yet.

My scenario again:

.45 Colt, 1-16" twist Ruger 5.5" barrel, my .452-300 with 76% meplat and .400" nose length, bullets driven to 1100' MV or less do not stay stable past 50-75 yards; drive them faster and they seem to stabilize better and show decent 100-yard accuracy.

I'd like to drive them slower, or reduce the weight and thereby reduce recoil while driving them faster, but am curious as to what, if any, impact there will be on stability (which is marginal right now) if I take a 20-25 grain plug out of the bullet's nose.

[youngda9]

No one is going to watch me shoot anything for proof
That's what I figured. LOL. Would be no skin off your back to demonstrate that it can be done since it seems almost unbelieveable. Nobody is asking you to show HOW you do it, just that you can.

Seems Larry hasn't been disproven yet. And I'm not surprised that nobody can prove him wrong. Seems quite simple to do...or perhaps not [smilie=1:

[dragon813gt]

I just want to know what "the secret" is. It's impossible to keep up w/ every thread. And I really have no clue as to what "the secret" is even hinting at. And if it was the holy grail so to speak. Shouldn't it be posted for all to see? Or is that asking to much?

[45 2.1]

That's what I figured. LOL. Would be no skin off your back to demonstrate that it can be done since it seems almost unbelieveable. Nobody is asking you to show HOW you do it, just that you can.

Seems Larry hasn't been disproven yet. And I'm not surprised that nobody can prove him wrong. Seems quite simple to do...or perhaps not [smilie=1:


Let's see... Larry posts pictures for proof. Gear posts pictures showing it can be done. Several people have posted threads about long range HV with accuracy Larry says can't be done. Larry wants to flit around and shoot with everyone and no one is biting. Can you possibly see what is wrong there?

BTW, all this viewing people shoot has been done before, and the witnesses were basically called liars also.

[youngda9]

Let's see... Larry posts pictures for proof. Gear posts pictures showing it can be done. Several people have posted threads about long range HV with accuracy Larry says can't be done. Larry wants to flit around and shoot with everyone and no one is biting. Can you possibly see what is wrong there?

BTW, all this viewing people shoot has been done before, and the witnesses were basically called liars also.
You know Larry would be more than happy to demonstrate as well. It's a question about long range high RPM accuacy that seems quite simple to answer. Nobody is willing to do it though. I see what is wrong there.

I'm not aware of any past get-togethers.

[jakec]

Yep, deformed bullets are not accurate.

Don Vernai get it now. i wasnt smart enough to get that from all the technical speak. it is very interesting but way over my head. thanks Don!

[Digital Dan]

That is the understanding I've always had.

I don't know if the folks here are declaring it to be completely wrong, or just hinting at some limitations to this as a rule of thumb, but I wish they'd explain themselves. My understanding is that with a typical pointed bullet, shifting the CG rearward (by way of hollowpointing the mold) shifts the CG further towards the center of the bearing surfaces of the bullet, which reduces the impact of irregularities in the portion of the bullet outside of the bearing surfaces.



C. Latch, I'll take a stab at an explanation of the physics and let you draw your own conclusions.

There are 3 distinct disciplines of ballistic science, Interior; Exterior and Terminal. They are generally studied or discussed as separate entities though it is clear there are relationships of performance throughout the overall package. As example, a cartridge with a heavy for caliber bullet and given charge will develop greater pressure than with a lighter bullet. The heavy bullet will have a greater sectional density than the lighter in this equation, thus if the forms are the same it will have a higher ballistic coefficient (BC). It will likely penetrate deeper in the terminal phase, all else being equal. There are a myriad of interrelationships within the three disciplines, but that does not preclude discussion on any one discipline on its own merits.

I mentioned earlier that conical bullets require the spin imparted by rifling to be stabilized in flight and the amount of spin required was largely related to the distance betwixt Center of Aerodynamic Pressure (CP) and Center of Gravity (CG). I am speaking of CG in context of its location on the longitudinal axis of the bullet, not as displacement laterally off of that axis.

Having stated previously that some projectiles deviate from this format due to design, I will restate that for the record. Among them are Forster style slugs commonly used in smoothbore shotguns, round balls, double ended and hollow base wad cutters and perhaps some Minie bullet designs. The have, by virtue of design and form, a CG that is at or forward of CP and as a result are dynamically stable. All others have reverse geometry and require spin to impart gyroscopic stability. In the absence of adequate gyroscopic stability factor (Sg) a conventional conical bullet will destabilize and ultimately tumble in flight. Sg is normally expressed as a non-dimensional value such as 1.3, that being a number generally accepted as a functional minimum for dynamic stability for conical bullets. Sg 1.0 is a value which suggests equilibrium, meaning that the overturning or pitching moments imparted by the CP are equal to the stabilizing force of gyroscopic momentum. It is not a functional value for use in the real world.

Bullet drag is compartmentalized to three regions of a bullet. Nose drag, shank drag and base drag. Within the realm of nose drag there are two primary regions of interest. 1) meplate cross sectional dimension and 2) ogive radius as expressed in calibers. The short version is that large meplates carry large drag penalties and short radius ogives do the same though to a lesser degree. With that out of the way, there is a wild card in the discussion and that is the variability of drag as relates to mach number. The highest drag regime for the purposes of this discussion is Mach 1. The velocities in close proximity to Mach 1 are known as the transonic range and are generally comprised of about Mach .75-1.25 give or take a small bit. This velocity range and the impacts of drag are greatly influenced by bullet form. The essence of the affair is that while the bullet may be traveling slightly below the speed of sound, the air in the flow field around the bullet's nose is supersonic because it has to move to move around the bullet, thus it is accelerated. Air is compressible at supersonic velocities and it requires a great deal of energy to do that. That penalty presents as aerodynamic drag.

Recall the previous about location of CG and CP please. The distance between CG and CP is a moment arm or a leverage arm if the term is more understandable. For a given form at variable velocity the CP will move slightly as a bullet transitions thru the transonic range due to alterations of the aerodynamic flow field. Alterations of density within the bullet form (ie, hollowpointing) will not have significant effect on drag if the meplate dimension remains constant. It will affect sectional density and thus BC. At the same time, removing mass from the forward portion of a bullet as just described will shift CG aft, thus increasing the dimension of the CP moment arm. Does this have an effect within the barrel? Draw your own conclusions. Does it change the metrics of Sg? Yes.

So, there are reasons that wide meplate bullets such as wadcutters do not present fine accuracy at distance from an aerodynamic perspective. There is substantial historical recognition of that fact. Likewise there are reasons that aerodynamically stable projectiles such as Forster slugs do not experience this phenomena.

As to the representation made earlier in the discussion and on assumption that concentricity of bore and bullet are necessary for accuracy, it may well be that such factors weigh heavily on cast bullet performance. My experience with jacketed bullets in various guns is such that some combinations are more acutely affected by that factor than others, meaning I've had some guns that were sensitive to bullet alignment to bore center and others not demonstrably so. I do not have enough experience with cast bullets to have arrived at a conclusion on that point. With that said, I will offer a few additional observations: 1) straight wall cartridges are much easier to load than bottleneck cases as relates to bullet concentricity. In fact, it is sometimes difficult to load straightwall cases that are not straight, or so has been my experience. 2) What happens in the bore and what happens in flight are two different subjects as far as I'm concerned. Gyroscopic stability does not exist within the confines of a barrel. 3) There is no such thing as a perfectly balanced bullet, be it cast or swagged, or with a jacket of any style.

[45 2.1]

This is actually funny, coming from you. We have observed... We do know what is happening... We also know how to cure that problem and have done so.

Here is how:
1. We reduce tolerance stack.
2. We do not shoot substandard dimensioned boolits, especially ones you use.
3. We pay no attention to the use of any 4895 powder or dacron.
4. We use a properly proportioned alloy suitable for the pressures involved.
5. We shoot boolits that actually fit the firearm that aren't undersized.
6. We load them to the required pressure level so they shoot properly.
7. etc.

All the effects you've noted occur with match jacketed bullets also.... and some of them shoot very tiny groups at long range, just like a good boolit does. You might want to look at a BP match grade boolit in flight from muzzle out to about 600 yards and see what it does, you might learn something there.


If we want accuracy, we need to understand what's going on. One can band-aid the real problem and get mediocre to decent results, or one can ascertain and correct the problem and get excellent results. To do the latter, gaining a deeper understanding of the "tolerance stacking" mentioned by 45 2.1 is a good place to start, but it is only a start.

It IS rather obvious that deformed boolits don't fly straight, one can fix the deformation or slow the rotation to where such deformation has less effect. Or one can do both.

Gear


I just want to know what "the secret" is. It's impossible to keep up w/ every thread. And I really have no clue as to what "the secret" is even hinting at. And if it was the holy grail so to speak. Shouldn't it be posted for all to see? Or is that asking to much?

See the top two quotes, they outline this supposed secret you think is there. All the parts have been elaborated on many times................................

[45 2.1]

You know Larry would be more than happy to demonstrate as well. It's a question about long range high RPM accuracy that seems quite simple to answer. Nobody is willing to do it though. I see what is wrong there.

I don't need a demonstration. I already know what a slow twist does, in jacketed bench rest and cast boolit bench rest..... and have known for a lot longer than the internet has publicly been online. If you want one of Larry's demonstrations, just ask him... I'm sure he will give you one, just be sure to post it with photos and another credible witness besides you along with all the things he asks of others. I know of no one on the forum who has witnessed any of his group shooting he has posted. I have had several members here while doing what I've said though. Just why Larry should be the arbitrator of what is possible is funny since he can't do what several people besides me have posted about long range HV shooting in 30 calibers.

[youngda9]

I don't know if you're planting a field of straw men, or you don't understand 45 2.1. I don't want one of Larry's demonstrations. Many of us want someone else who claims to do what Larry says highly unlikely to take him up on his offer. Demonstrate it to Larry that you can do what you claim. He'll show up on your doorstep and bring lunch.

Just posting more on the topic does not give you any more credibility. Say all you want. I've read many many things from keyboard commandos on the internet that I know not to be true. This one, I'm not sure about...that is why I want to have people come together to sort it out. It would only take a couple hours out of your time...but I know that's probably too long to pull you away from your keyboard. :kidding:

As far as I can tell there's a reason why his challenge cannot be accepted. You don't want to prove him right. Because if someone could prove him wrong, I'm sure they would. They could also have a nice chat and learn a lot from one another I'm sure. I've read of countless people losing accuracy, especially at distances of 200-300yds, right in the RPM range Larry suggests. And then when someone comes along and says they can shoot sub 1.5 MOA at 169,000 RPM they disappear when asked what the group size is at 200 and 300 yards. Notice how gear never answered my question about that waaaay back yonder in post #61. (I'm sure the answer is that he hasn't shot em out that far anyways....)

[ShooterAZ]

youngda9,

The challenge will never be accepted because this feud has been going on for so long that they have a deep resentment (if not hatred) for each other. It's too bad, because the accumulated knowledge regarding boolit casting & shooting with these guys is incredible. I would love to see them iron this thing out, but as you can see it's highly unlikely to ever happen due to "the feud". Each one has his own opinion on what is happening, and you have to respect it for what it is.

[youngda9]

I understand that. And I agree that it's sad. But it's easy for one side to prove that it can be done. Larry can't prove a negative.

[C. Latch]

Dan,

Thanks for the explanation. Most of that was familiar to some degree, but this:

The distance between CG and CP is a moment arm

Was something I don't remember ever being exposed to, but it makes perfect sense, and is a great help to my understanding of the subject at hand.

So what I'm left with is that hollowpointing the mold in question will, with mathematical certainty, improve the Sg of my bullets. I suspected this, but now have a much better basis for understanding this.

Now the question left is: Will the improvement be significant enough to justify the endeavor?

If I lose ~20 grains off the nose cavity of my bullet, I can shoot it at the highest speed I've previously shot it, but lose 6-7% of my recoil in the process, which is a significant amount, and, with the improved Sg, may be able to actually slow it down a tad more, reducing recoil further while maintaining acceptable accuracy.

Right?

If I could go from a 300-grain FN at 1250' to a ~275-grain FNHP and either keep my speed the same (1250'ish) or reduce it slightly (1150' to 1200'ish) I think that would greatly please me and still be extremely effective on deer.

[C. Latch]

We pay no attention to the use of any 4895 powder or dacron.............

What does this mean? I'm familiar with the concept of using a filler such as Dacron, but why the reference to 4895?

I've never loaded 4895 over cast bullets, but know that it's common for some folks, and just last night I loaded some IMR4895 for a rifle with jacketed bullets, but......what's unique about 4895 that caused you to reference it in your list of stuff you avoided for accuracy?

[35remington]

It's a dig at Larry because he frequently uses 4895 and Dacron.

It could have been left unsaid.

What would settle the whole thing is a demonstration of principles at something like a CBA match, but heaven forbid this ever gets resolved on any official record with number to back it up.

Those here are much more practiced and accomplished affecting a "holier than thou" and "the other guy is a moron" attitude than they are at respectful analysis and exchange of information.

Some of the participant's condescending attitudes are especially tiresome. It would be nice to see an exchange of useful info rather than the usual heat and no light.

[ShooterAZ]

Agreed. Trying to learn anything here has become clouded with "attitude". Please keep it civil here.

[Digital Dan]

Dan,

Thanks for the explanation. Most of that was familiar to some degree, but this:

The distance between CG and CP is a moment arm

Was something I don't remember ever being exposed to, but it makes perfect sense, and is a great help to my understanding of the subject at hand.

So what I'm left with is that hollowpointing the mold in question will, with mathematical certainty, improve the Sg of my bullets. I suspected this, but now have a much better basis for understanding this.

Now the question left is: Will the improvement be significant enough to justify the endeavor?

If I lose ~20 grains off the nose cavity of my bullet, I can shoot it at the highest speed I've previously shot it, but lose 6-7% of my recoil in the process, which is a significant amount, and, with the improved Sg, may be able to actually slow it down a tad more, reducing recoil further while maintaining acceptable accuracy.

Right?

If I could go from a 300-grain FN at 1250' to a ~275-grain FNHP and either keep my speed the same (1250'ish) or reduce it slightly (1150' to 1200'ish) I think that would greatly please me and still be extremely effective on deer.


Moving CG aft increases the moment arm, thus Sg is reduced if all else remains equal. The reduction may or may not be compensated for by increased velocity depending on particulars.

[C. Latch]

Moving CG aft increases the moment arm, thus Sg is reduced if all else remains equal. The reduction may or may not be compensated for by increased velocity depending on particulars.

Wait.

You're saying that moving CG rearward reduces stability?

Nevermind on my saying that made sense. If the CG is in a given place and the nose (where the CP is, more or less) acts upon it as a lever, then moving weight out of the nose should reduce the moment, therefore effectively increasing stability....right?

What am I missing here?

[C. Latch]

On second thought:

I'm understanding that the moment between CG and CP would be based not only on the length of the arm but also the weight at either end, in which case removing weight from the CP area of the bullet would make inconsistencies have less effect (even if the length of the arm were to increase slightly.....right?).

Which is the weightier factor here, the weight of the projectile (or portion thereof) being acted upon by drag, or the drag itself?

If I'm reading you correctly, you're saying my HP idea would, in essence, make things worse, right?

[Digital Dan]

If all else is equal, the sum of aerodynamic forces will not change significantly nor will location of the CP as a result of your proposed modification. The CG will move aft, thus increasing the length of the moment arm (same force, longer lever), so yes, it will have an adverse effect on Sg, albeit small in measure. Whether or not elimination or redistribution of mass will, for other reasons, have a positive effect providing net benefit is an open and separate question. What is presented here relates only to that portion of the bullet's travel from muzzle to target and the metrics of gyroscopic stability, nothing more.

In the video at the beginning of this thread we saw bullets departing from "controlled flight" due to modification of nose form. Such modifications changed location of both CG and CP, resulting in substantial upset of equilibrium and demonstrably wild gyrations where Sg struggled with upsetting moments. Your idea will modify only CG location if properly executed. My thoughts and they are speculative in nature, the net change that will result from your modification will have no significant effect on Sg for your bullet. Emphasis on "significant". Whether or not it will address the issues you have experienced is something I would not forecast. I rather suspect the problems you have encountered are more likely associated with the wide meplate of your bullet and drag forces associated with the transonic velocity range. Have you ever tried loading it around 1,000-1,050 fps to see what it will do out at 50 yards or so?

[C. Latch]

I rather suspect the problems you have encountered are more likely associated with the wide meplate of your bullet and drag forces associated with the transonic velocity range. Have you ever tried loading it around 1,000-1,050 fps to see what it will do out at 50 yards or so?

When I started down this road, I started with a Lee 452-300-RF bullet that has an 80 to 81% meplat, depending on who's measuring, and I quickly learned that 80% was too much to be made stable at the velocity I wanted to shoot.

I then went to the 76% design, thinking I might run at the very edge of what I could get away with in terms of stability relative to the speed I wanted to shoot at. Not properly taking into account the reduced pressures associated with a longer nose, my first loads were in the 1000-1050' range you ask about, and 25 yard accuracy was decent but at 50 yards they were already deteriorating.

From what I can tell, my most accurate speed so far has been between 1150 and 1200, but this load is (I'm not looking at my notes, this is from memory) falling apart by 75 yards or so. The load I settled on last season was around 1250' IIRC and would hold 6" at 100 yards. Good enough to kill deer at handgun ranges, but not good enough to suit me.

It seems to me that the bullet I'm casting now would be an excellent design if I pushed it even harder and found accuracy at the 1300+ range, such as one might do for bear defense, etc, but such a load would be grossly overkill (for someone such as myself who is recoil-averse) on whitetails.

In light of that, my current thought is to keep this mold (~.34xx" meplat) for possible future use, but not pursue the HP idea; instead, I will stay signed up for a group buy of a 300-grain HP that has a smaller (~.31xx") meplat and has proven to be stable enough in the past.

Once that mold is here and I experiment with it, I may or may not experiment further with ~.32xx" meplat mold that will drop at around 270-280 grains.

My goal here is to find the best possible design, with 'best' being defined as a bullet that allows me to be 'hunting accurate' out to 125 yards or more, while keeping recoil as light as possible while still maintaining enough weight and velocity to penetrate completely on a deer yet having a meplat (or expanding HP) that will crush the maximum amount of tissue on its journey through a deer.

It may well be that the new mold I'm signed up in the group buy for will be stable enough to allow me to shoot it in the 1100' to 1150' range (MV) and perform well on deer without the recoil associated with hotter loads. Time will tell.

In the meantime, thanks for the patience in explaining these things to me.

[Larry Gibson]

Kerrville, 11 am. What a shame to pass up a chance to show me how you do it.........:(

Larry Gibson