RPM theshold discussion

[Larry Gibson]

Gear

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

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

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

Larry Gibson

[Larry Gibson]

Iron Mike Golf

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

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

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

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

Exactly correct as I stated.

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

Larry,

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

http://www.nennstiel-ruprecht.de/bul...ria.htm#header

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

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

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

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

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

All correct.

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

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

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

Larry Gibson

[Iron Mike Golf]

Larry,

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

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

[onesonek]

Onesonek

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

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

Larry Gibson

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

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

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

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

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

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

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

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

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

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

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

[madsenshooter]

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

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

[felix]

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

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

... felix

[Larry Gibson]

Iron Mike Golf

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

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

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

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

Larry Gibson

[Iron Mike Golf]

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

... felix

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

[Larry Gibson]

onesonek

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

Larry Gibson

[Larry Gibson]

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

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

Larry Gibson

[geargnasher]

Gear

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

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

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

Larry Gibson

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

Gear

[Larry Gibson]

Onesonek

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

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

Larry Gibson

[Larry Gibson]

Gear

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

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

Larry Gibson

[Iron Mike Golf]

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

Larry Gibson

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

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

[waksupi]

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

[onceabull]

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

[leftiye]

Gear

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

Larry Gibson

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

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

[45 2.1]

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

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

[onesonek]

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

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

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

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


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

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

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

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

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

[Larry Gibson]

Onesonek

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

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

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

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

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

Again, thanks for the productive input.

Larry Gibson