RPM Test; a tale of three twists, Chapter 2

[runfiverun]

tube_ee
of course statistically a larger boolit should have more errors [ as any larger sample of anything would]
speed is nnot the only issue here it is speed combined with accuracy, with accuracy being the judge.
the question is ,is the rotational force the limiting factor to accuracy.at higher speed

welcome to the forum join in and have fun.

[KYCaster]

Well, I really should know better, but I'm gonna jump in here anyway.

I can't claim to have any particular expertese in this subject and often have a hard time wrapping my mind around some of the concepts presented here, but generally I can eventually understand what you guys are talking about. One thing I do have is a pretty active BS meter.

I become a bit dismayed when a discussion degenerates into "piling on". For example, the terms centrifugal and centripetal...I have always used the term centrifugal and now that I know that there is a difference, I'm still not sure how each should be used. I would welcome any attempt to educate me when I use the wrong term, but please try not to insult me when you do it. And one more thing...an obvious typo or brain fart should be recognized for what it is. If, in an agitated state of mind, someone types "fps" when "rpm" is obviously the intent then, by all means, call the error to his attention and ask that it be corrected or clarified, but PLEASE, do it politely. Try to keep the demeaning remarks to yourself, they add nothing positive to the discussion and damage the credibility of the person stooping to those tactics.

I admire Larry for taking the initiative to to try to prove (or disprove) a theory that he believes and think he deserves all our support. If you disagree with his methods or his eventual conclusions, by all means pick them apart, we'll all be better off for the knowledge gained, but some of us (I'm sure I'm not the only one) are getting a little weary of the playground tactics.

So, now that I've alienated most of the people involved, a couple of specific points I'd like to address:

Larry,
If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

Ralf

The RPM numbers that appear are deffinitely NOT identical. The revolutions per distance traveled are identical...that's a constant dictated by the twist rate, but the revolutions per minute vary with the velocity.


And Shannon says:

"Even if defects are not randomly distributed, (not evenly distributed, there's a difference), so that there was some mechanism at work that could be correlated to where the voids and/or density variations showed up in the actual bullets, the larger bullets would still have more places for those defects to be where they could have a larger effect.

If, for example, there was a tendency for defects to cluster near the outside edge of the bullet, (like the differential cooling rate might produce... just thinking out loud,) then in that case the smaller bullets would shoot better, because their outside surface is closer to the centerline. Similar logic holds for anywhere you want to cluster the defects along the radial axis of the bullet."

Cast boolits will always have variable density because cooling and solidification take place from the outside of the mold cavity...heat is conducted away from the alloy through the metal mold block and radiated into the surrounding air...causing the surface of the boolit in contact with the mold block to solidify first and most of the shrinkage to be drawn from the still molten alloy at the center of the boolit. This leaves the center of the boolit less dense than the shell, and in extreme cases will leave a void in the center.

Multi cavity molds will have an effect on the position of the lower density area because the heat loss is not equal around the circumference of the cavity, The mold will always lose heat slower where the cavities are close together thereby causing lower density parallel to the parting line.

Some casting techniques are supposed to reduce this effect, but casting with a single cavity mold would be the only way to reduce the effect to an absolute minimum.

BTW, Shannon, welcome to the cast boolit forum. Despite some of the sniping going on in this thread, the people here are generally well behaved and have the best interests of the casting fraternity in mind. Sometimes a heated discussion is the best way to sort out our differences and reach a conclusion that will help advance the art of boolit casting.

Thanks to all who have contributed to this discussion.

Jerry

[Larry Gibson]

Ralf

Your problem seems to be the formula for getting rpm from the velocity and rifling twist data. You are stuck on time and it's obvious. That formula give you rpm, which we know is revolution per minute. You are not seeing that in 100 yards that the bullet time of flight is in fractions of a second. Let's look at what 45 2.1 said as he said what I was trying to say much better and in more plain terms:

It is not a problem. The tests so far have indicated that. I am not stuck on time. It is RPM, M stands for minute. That IS time. It is in the equation, to take it out is meaningless.

If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

That is correct; the bullet will turn the same number of revolutions in distance. I have said that before and in this thread. The problem is you are taking out the "time", i.e. the M part of the equation. The faster the bullet travels the distance the higher the RPM. It is that simple and you can figure it anyway you want and it's not going to change.

I am not the judge of people in this thread on rpm but from reading what various people have written a few have a correct understanding of what 45 2.1 is saying. He is right. One person is stuck on writing a book the other too focused on rpm as the damaging factor to high velocity cast bullet acccuracy.

45 2.1 is wrong. I really don't care how you judge me. Judging me does not matter. You need to judge the facts. 45 2.1 has the facts wrong. If you side with his judgement then you are wrong as it is contrary to the facts. I am not "stuck" on anything, the tests are proving RPM is the culprit.

Larry it's not the rpm. One other thing you haven't looked at is that shooting at very high velocity increased the recoil. Take the 30-06 with a twist of 10 and lets use the Lyman 311284 or the Lyman 311299. Both of these bullets are over 200 grains. In order to get them out of Larry Gibson's rpm range on the high side requires what I think is a very high velocity which is going to have much more recoil then a bullet that is lighter and shot within Larry's rpm range for accuracy. I will tell you where I am going with this. None of you here will dispute that a shooter can shoot more accurate with a rifle that doesn't have a lot of recoil. In order to prove Larry's theory a rifle would have to be fixed in a solid firing device that would take all the human error out of the testing.

It is the RPM, the tests are proving it. I can shoot 1/2 MOA goups all day long with 175 gr MKs at 2680 fps out of that M70 .308. That load has more recoil than the 177 gr cast bullet at 2400 fps. So why is recoil not making me shoot bad groups with the 175 gr MK? It doesn't is the answer. You also are grasping at straws along with 45 2.1.

To just touch on why jacketed bullets are much easier to shoot accurately at high velocity then a cast bullet I say one reason is that they don't exactly duplicate the shape of a jacketed counterpart. I will say that bases on jacketed bullets are more near perfect then a cast bullet's base.
In all my time shooting cast bullets I have never found a plain base bullet that showed melting. I have found many that showed gas cutting. I view gas cutting more of a pressure thing from the gas then of heat. There may be some softening of the bullet alloy near edge corners of the base to help the gas cutting. I think that most the damage that is done to a cast bullet is done inside the bore of the rifle. I have seen cast bullets shot at very high velocity that didn't not leave a smoke trail and they did not disintegrate in flight. I am not claiming that they were very accurate and only make that statement to show they can hold up to a very high velocity.

Just what the heck does shape of the bullet have to do with recoil? I suppose you and 45 2.1 will come up with some bastardized way of interpreting the formula on calculating recoil(?). Excuse me but that is just too far fetched for me to waste any more time on.

Larry Gibson

[felix]

I agree, Jerry. Only Larry should call the deal off, and I hope he does not until all of his "facts" are in for us all to see. Yes, I would like to see a practical limit/threshold in RPM be established and I hope we don't have to resort to single banger molds to increase that limit a significant amount. If so, so be it, let's start ordering single bangers. ... felix

If I had any single bangers, I would gladly submit mine to him for use to augment his final statistics with his molds. ... felix

[Larry Gibson]

felix, jerry

I don't think we need to go to just single cavity moulds. Granted single cavity mouldshave been proven to provide the most accurate bullets as they are consistent from the same cavity. However, bear in mind I am not attempting to find the most accurate loadfor each rifle. I am only trying to fnd where accuracy begins to be lost. I m looking at when accuracy begins to get proportionally worse.

Larry Gibson

[Tiger]

Jerry,

You are partially right on voids and shrinkage. There is a good write up about it in the NRA Cast Bullet book. Most common molds of today are bottom pour. The heat does radiate from the molten alloy to the block and then to the surrounding air. A good portion of the heat goes to the sprue puddle and this is where you can see the shrinkage and often a void. This shrinkage area in a bottom pour mold is near an important part of the bullet, the base. The NRA article said they sectioned many bullets and of equally different calibers that were correctly casted and found no voids. That's important to absorb the words correctly casted. They went on to say casting that was not done correctly then found voids. Yes, in the center like you stated. I see that mention of a single cavity mold was brought up but nobody so far mentioned holding the mold sprue plate against the spout of a bottom pour furnace to get a full fill of the mold and helped by the pressure of the molten alloy in the pot. Wouldn't this give you the best possible void free bullet?

Yes the rpm is there where the formula for it says that it is but it becomes again a factor of time. What I mean is that the bullet is in flight such a sort amount of time I do not believe the rpm has much time to work on damaging the bullet in whatever way some think that it is doing.
Just like the hot flame of the powder burn. It is hot enough to melt the bullet alloy but it doesn't have enough time to act on it. You know like when you touch something that is hot very quickly with your finger as oppose to touching it a longer period of time.

I think in the end many are grabbing at excuses. First and still, the rpm. Then the many different descriptions of centrifugal force. Then the composition of the alloy in the bullet and how it solidifies. Paper patching was brought up and nobody is looking there to the reason why they can be shot at high velocity with respectable accuracy.

There are shooters who get accuracy at high velocity with cast bullets and there are shooters who don't. Who can explain that to me?

Larry hang in there and continue with your test. I can say that at least you are trying and doing something to come to a conclusion.

Ralf

[45 2.1]

It is not a problem. The tests so far have indicated that. I am not stuck on time. It is RPM, M stands for minute. That IS time. It is in the equation, to take it out is meaningless.

If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

That is correct; the bullet will turn the same number of revolutions in distance. I have said that before and in this thread. The problem is you are taking out the "time", i.e. the M part of the equation. The faster the bullet travels the distance the higher the RPM. It is that simple and you can figure it anyway you want and it's not going to change.
So, what your saying is it takes (0.1875 - 0.125) = .0625 seconds less to damage a boolit than what the original 0.1875 seconds didn't? It's traveling faster, so has less time to damage it. Explain it, if you will if time or RPMs is the culprit ..................

I am not the judge of people in this thread on rpm but from reading what various people have written a few have a correct understanding of what 45 2.1 is saying. He is right. One person is stuck on writing a book the other too focused on rpm as the damaging factor to high velocity cast bullet acccuracy.

45 2.1 is wrong. I really don't care how you judge me. Judging me does not matter. You need to judge the facts. 45 2.1 has the facts wrong. If you side with his judgement then you are wrong as it is contrary to the facts. I am not "stuck" on anything, the tests are proving RPM is the culprit.
Just how am I wrong? Since you haven't finished and posted a conclusion, your statement would seem premature. Or is something else going on?

Larry it's not the rpm. One other thing you haven't looked at is that shooting at very high velocity increased the recoil. Take the 30-06 with a twist of 10 and lets use the Lyman 311284 or the Lyman 311299. Both of these bullets are over 200 grains. In order to get them out of Larry Gibson's rpm range on the high side requires what I think is a very high velocity which is going to have much more recoil then a bullet that is lighter and shot within Larry's rpm range for accuracy. I will tell you where I am going with this. None of you here will dispute that a shooter can shoot more accurate with a rifle that doesn't have a lot of recoil. In order to prove Larry's theory a rifle would have to be fixed in a solid firing device that would take all the human error out of the testing.

It is the RPM, the tests are proving it. I can shoot 1/2 MOA goups all day long with 175 gr MKs at 2680 fps out of that M70 .308. That load has more recoil than the 177 gr cast bullet at 2400 fps. So why is recoil not making me shoot bad groups with the 175 gr MK? It doesn't is the answer. You also are grasping at straws along with 45 2.1.
I don't have a horse in that race. I and several others on this board have already been where your trying to go (whether you believe it or not). We all have posted what you need to look at to get there. If your choice is to ignore those posts, fine, but do not call us wrong when you haven't got there. The "I can't do it, you can't either" attitude doesn't work here.

[Tiger]

Larry

Your theory is that when cast bullets are shot above your rpm range that the accuracy won't be as good. The same bullet shot inside your rpm range will be correct? Then tell me why many others on this thread keep posting other ideas of why the bullet isn't accurate above your rpm range. Do good cast bullets magically develop voids when shot above your rpm range?

Ralf

[Larry Gibson]

45 2.1

"So, what your saying is it takes (0.1875 - 0.125) = .0625 seconds less to damage a boolit than what the original 0.1875 seconds didn't? It's traveling faster, so has less time to damage it. Explain it, if you will if time or RPMs is the culprit .................."

I never said the bullets are damaged by RPM. The centrifugal force acts upon the imbalances already in the bullet. Those imbalances are there because of design, casting or were created during acceleration. And yes the time of flight the less the effect the RPM will have. This is why I always say for rifle loads 50 yards is not a good indicator of accuracy. It needs to be 100 yards minimum. The longer the range the greater the effect because the bullet is in flight longer.

"Just how am I wrong?"

So far you are totally ignoring the results of the test so far. Every time I ask you to look at it or refer back to those results you ignore the results, don't answer the question and go off on another accusatory tangent. Look at the results of the test completed so far and post questions regard those results. Abstract theories with no test results do not prove anything.

"I don't have a horse in that race. I and several others on this board have already been where your trying to go (whether you believe it or not). We all have posted what you need to look at to get there. If your choice is to ignore those posts, fine, but do not call us wrong when you haven't got there. The "I can't do it, you can't either" attitude doesn't work here."

Sorry, I forgot to put who that part referred to. You do not seem to understand. I am not trying to go where you have been. You, Bass and other claim good accuracy at high velocity. I have been there too.

What I am trying to prove is the existence of the RPM threshold. How that threshold adversely affects the accuracy of regular cast bullets in rifles. Why certain designs of bullets can only be pushed into or through that threshold so far. And what it actually takes to push through that threshold to attain considerably higher velocity. I am unaware that you have conducted any tests to prove or disprove the RPM threshold. I know you have posted how to push the 6.5 Swede up to 1800 fps or so as we have traded information on that. However those methods and results only prove the existence of the RPM threshold in an indirect way. Are there other tests?

Larry Gibson

[Larry Gibson]

Ralf

Your theory is that when cast bullets are shot above your rpm range that the accuracy won't be as good. The same bullet shot inside your rpm range will be correct?

That is the basic precept.

Then tell me why many others on this thread keep posting other ideas of why the bullet isn't accurate above your rpm range. Do good cast bullets magically develop voids when shot above your rpm range?

The ideas several post are part of what we are looking at. Ideas of others ignore the facts and results of the actual tests. They offer no test results to demonstrate their ideas, only abstract theories. I point out the problem with those abstract theories and use test results or refer to scientific laws. A couple others just present ideas that are off on tangents for what appears to be just argument.

Your preconceived answer to your own question is incorrect. The bullet may have a void, if so then it occurred during casting or prior to the flight of the bullet. As I’ve said before; the RPM affects the imbalanced bullet. The imbalances occur prior to flight. It is during flight where the RPM affects them.

This test is directed at proving and demonstrating the existence of the RPM threshold. Sor far the results of the test are proving that. Questions and comments regarding this test should be relevent and should have factual test results to back them up if contradictory to this test results. Just giving some uproven abstract theory or idea is not the correct way to further meaningful discussion. If anyone has some proof (actually results not just an idea) that the results of the test are incorrect then I certainly want to hear it.

Larry Gibson

[Tiger]

Larry,

I didn't preconceive my answer. I'm throwing things out there to jog your mind which it seems that I have done. We are getting somewhere now that you have basically said that others are just throwing ideas and some for the sake of just to get into the argument. That basically says that just a few know what they are talking about.

According the NRA article in their Cast Bullet book, voids created by shrinkage in the mold are almost always centered. They went on to say that such centered voids didn't upset the bullet balance much. They also said that such voids could be almost totally eliminated by better casting techniques, but casting techniques is a whole other subject.

Here are some more things I will throw out to you. I think the bullet lube, the fouling that gets into the bore, and temperature when shooting are things that have an effect on accuracy not only at low velocity, but more so at higher velocities. When I talk about bore fouling I not only talk about fouling which is very obvious to the naked eye but also what the naked eye can not see. I think that fillers play more of role then just positioning the powder charge. I feel they some how condition or clean the bore, along with sealing gases from getting past the bullet base. We know that in many instances that shooting a large quantity of cast bullets that the accuracy can decline. That is obvious that fouling can destroy the accuracy so any means by which you can prevent or limit the fouling can be beneficial.

What say you Larry?

Ralf

[Larry Gibson]

Ralf

I'd say you got some pretty good ideas there and are tracking. Also, I don't want to give the impression that those who want to argue don't know what they’re talking about. They most often do. They just need to put those ideas in a constructive way and, if contradictory to this tests results, then give evidence by way of tests, either their own or someone else's. They also must understand that the tests they provide must stand up to scrutiny and be relevant to the discussion.

Centered voids can cause problems at higher velocity as we are pushing at higher pressure. The bullet can collapse unevenly into the void unbalancing the bullet. This is just as the bullet can collapse unevenly in the lube grooves.

All the things you discuss are good examples of things that can happen to the bullet. Keep in mind those things happen internally in the barrel. We are measuring the internal ballistics. Hopefully we can catch those anomalies when they appear. They all affect the balance of the bullet. However, again keep in mind; it is the RPM that affects those imbalances during the bullets flight. The imbalances by themselves do not cause the inaccuracy.

Larry Gibson

[felix]

Ralf, voids can only be minimized by casting techniques, never eliminated, and not even close to being eliminated. Heavily swagged wire is the norm for bullet cores to eliminate wire making voids. If there is going to be a jacketing operation in your future, even for paper patch, the boolit being further swaged into shape should come from wire and not from a mold. For proof, take any cast boolit/core and throw it into a polishing gadget. Eventually, you will see the air holes appear all around the object. On a side note, I prefer boolits with shallow rounded grooves. The boolits seem to be tougher with this arrangement, as by measuring the increased spring back they have when compared to those with a large square groove from the same pot of lead containing enough antimony to make it happen like so. ... felix

[leftiye]

Larry, You just walked right through the middle of one of my main problems with this whole process. That being that in your process of sorting out the factors which do or may affect accuracy you are only considering a small portion of the arguments presented. As Tiger said, this reflects a certain lack of respect for those whose ideas you refuse to address. I don't think of it as lack of respect on your part, just a somewhat misguided way of looking at what deserves to be considered.

For example, internal (ballistics) factors that have long been known to cause inaccuracy due to loading techniques (the only thing we reloaders have control over), and what happens during acceleration in the barrel aren't to be given air time because they occurred prior to the boolit leaving the muzzle. Casting defects aren't to be considered because they occurred even before internal factors. Pressure effects at the muzzle, poor crowns, deformed boolit bases at exit from the muzzle are other thangs that don't qualify for some other reason. Paper patched boolits going faster than they're supposed to while still being more accurate than they should be aren't allowed, you only want to deal with plain cast boolits. Several factors that affect accuracy DURING FLIGHT (one possibly vastly more destructive to accuracy than RPMs - bullet deformation from friction in the air, and it will happen at some velocity less than 3300 fps) recieve no comment whatsoever. Calculating ballistic coefficient doesn't adequately cope with boolit deformation in all of its sources, especially when it doesn't compare BC at exit with terminal BC (it only indicates that something was wrong, something that is not necessarily related to deformation).

I have never done anything that resembles a SCIENTIFIC test with regards to any gun related concept. I have no fear whatsoever that my ideas, and principles with regards to reloading are more than minimally faulty. To totally reject ideas proferred (most of which are reloaders theories of long standing, and doubtless correct - it is inconcieveable that were scientific tests were performed that most of these would be found faulty) simply because the writer doesn't support the idea with referrences to scientific findings is a cop out. Sounds mostly like you just don't want to experience the frustration with "them there heretics".

As I've said before, if you only want to study the effects of RPMs on accuracy, this is a worthy study, but you should present it as a study of a narrow, restricted part of cast boolit accuracy, not the whole banana. Virtually everybody here accepts that RPMs have an effect, and that at some rotational speed it will become an unsurmountable obstacle to accuracy, but that's enough said. For my money there's more going on. RPMs isn't THE culprit (to quote you), it's only one of many issues to be overcome.

[Tiger]

Felix

Yes that is true of the voids that one can not see with his naked eyes. You have to admit from some of the excellent targets shot at matches come pretty close to a bullet with no voids. Some say that Electro Type metal doesn't shrink but I read that is a myth because it fills the mold out more sharper then most any other alloy giving it an appearance that it doesn't shrink. Maybe it would be a good metal for casting for high velocity accuracy.


Leftiye

Good post that looks like you are thinking very hard. I would like to know at what velocity friction from the air really starts to melt a cast bullet.

What would be wonderful is if a high speed video could be taken of a cast bullet shot out of Larrys rpm range and out of a fast twist rifling to see what is happening, if and when it starts to wobble.

Some have compared the balance of a cast bullet to that of an automobile tire. We know know what happens when your tire is not in balance. It's a vibration but that is all. Your wheel doesn't fly off your automobile. What would happen if the bullet does vibrate a little from being out of balance?

[leftiye]

Tiger, Thanks for the kind words. Actually, I think Larry has a valid hypothesis, as I said. The situation with nose melt at some high velocity seems unavoidable. It will be an insurmountable problem. I understand that some jacketed bullets are having a similar problem in excess of 4000 fps. One might guess that before that happens the jacketed boolit jacket becomes a container with at least part of the lead being molten (and the rest being very soft - talk about varmint bullet!). Way before the boolit nose deforms visibly, heat will soften the boolit, and RPMs will probly bend it or cause some other deformation that destroys accuracy. I also see this heating of the boolit base by powder flames acting in conjunction with pressure as possibly explaining the fact that plain bases which supposedly don't melt fail at moderate pressures which are not supposed to be high enough to overcome the plastic fail strength of the lead. If these melting/pressure phenomena were to happen at around Larry's RPM (barrier) threshold it WOULD be fun to watch. I suspect that the RPM thang will come first (at lower velocities) though.

[runfiverun]

SPEER 30 CAL [.308] 125GR
"TNT" HOLLOW POINT

these high-energy, thin-jacketed varmint bullets
are designed for total disruption upon contact.
they are especially recommended for the 308, 30.06
and other dartridges in this velocity class. they
give maximum accuracy at these velocities.

NOT RECOMMENDED fo use in rifles having
twists quicker than 1 turn in 10 inches. DO not
exceed velocities of 3100 feet per second.




hmmmmm..............somebody want to give speer a call ???

less than 3100 fps nor faster than 1 in 10
wonder how they come up with this.

[Larry Gibson]

Leftiye

Let me try this one more time.

“you should present it as a study of a narrow, restricted part of cast boolit accuracy, not the whole banana”

That is exactly what I am doing. It is you and a couple others that do not see that. Please go back and read Chapter 1. It explains it. I am not “sorting out the factors which do or may affect accuracy you are only considering a small portion of the arguments presented”. Those “factors” are factored in so I can focus on the specific aspect of how RPM affects the cast bullet.

Once again I shall explain it; I am not trying to develop the most accurate load for any of the rifles. Is that plain enough? I do not need to develop the most accurate load. If the rifles shoot 1.5 - 2 moa in or below the RPM threshold and 3 -7 moa above the RPM threshold (depending on the twist) with the loads I am using that proves the same point as if I go to all the trouble to find the most accurate load for each rifle and they still shoot 3-7 moa above the RPM threshold. The result is the same; the accuracy decreases above the RPM threshold. Is that so hard to understand that we do not need the “most accurate load” to find out what we need to know. By using a proportional comparison of the accuracy of each rifle to the proportional accuracy of the other rifles the results are the same. Even if I fine tuned the load and all three rifles shoot 1 moa or less and if they shoot 2-3 moa above the RPM threshold at the same velocity the result is the same. If the 10” twist shoots proportionally larger than the 12 and 14” and the 12” shoots proportionally larger than the 14” twist all at the same velocity then the result is the same. That result is that RPM is the culprit.

I am casting good bullets with a good alloy and visually culling those with obvious defects like voids in the base, voids anywhere else, with non filled out spots and bad bases. The GCs are Hornady’s and are pre-seated with the Lyman 450 before sizing at .309 and lubing. I am using cases that are matched prepped and fire formed to the rifle. They are neck sized in bench rest dies. I am using new H4895 and other powders. The primers are Winchesters. The lube is Javelina, a very proven lube. The rifles are all moa or capable of sub moa. They do not have bad crowns or bad bores. They shoot very well with both cast and jacketed bullets.

Actually all three rifles shoot the 311291 bullets quite accurately. If there were any of the consternated over problems you and some are having they would not shoot them well at all. Would they? That is why “other thangs that don't qualify for some other reason” because they are not applicable.

The point is; those three rifles all shoot those bullets well in the RPM threshold. All three rifles begin to lose accuracy above the RPM threshold. The 10” twist loses proportionately more than the 12” and the 14”. The 12” loses proportionately more than the 14”. Pressures are the same, velocities are the same, and the only thing different is the RPM and accuracy. So guess what?

First you chastise me and my test for this; “you should present it as a study of a narrow, restricted part of cast boolit accuracy, not the whole banana”, then you chastise me and my test for this; “Paper patched boolits going faster than they're supposed to while still being more accurate than they should be aren't allowed, you only want to deal with plain cast boolits.” You don’t even know which way you want it…..

Now if any of you feel slighted I perceive is not because I “reflects a certain lack of respect for those whose ideas you refuse to address”! It is I who should feel slighted because you and some others all show a lack of respect for me by not reading what I write. I continually have to tell you and others over and over again what I am doing and why I am doing it and to look at the test results. You and others continue to ignore the obvious. If you feel that is a “somewhat misguided way of looking at what deserves to be considered” then feel free to conduct your own test and report back the results. I’d be more than happy to see your results.

Conceive or proffer what you will, when those “reloaders theories of long standing, and doubtless correct” are contrary to test results and those who proffered them do not provide test results to prove their theories then I probably will continue to “cop out” and not support the unproven or untested theories of “them there heretics.”

I just got to your last paragraph and I’m wondering why I’m wasting my time on someone who agrees then disagrees in the same paragraph.

Larry Gibson

[Bass Ackward]

Good discussion. Glad other folks are joining in.

Talking with another local fella here. He said assuming perfect bullet flight, air flow from the right or left could make a bullet either rise or drop depending on the direction of the wind and the direction of the rotation. (Right or left hand twist) He said that the steeper the angle marks on that bullet, the greater the diverting effect.

Which translates out to the faster the twist, the greater the movement will be with the same wind. Obviously, bullet speed when thought of in MPH makes it easier to understand that as velocity increases, the negative effect increases too. Much like changing the pitch on a proper blade. This would definitely support the results seen with the RPM theory, as Larry says that even when things are done right, best accuracy is always down low. Just not necessarily from an outta balance standpoint that he is focused on. Especially when one considers the negative that grease grooves play in the BC equation, this effect would be amplified on cast bullets compared to jackets.

So separating these things out to a single factor is not easy. It might be that each has a stronger effect at different points on the scale. The scale being defined by cartridge volume, barrel length, and bore diameter and the twist rate required by that bore diameter. Which is why I suspect the people that came before us adopted the generalities to 1. use the slowest twist required to stabilize, 2. use the longest barrel possible, and 3. use the best ballistic coefficient bullet for longer range use. (a lighter per caliber bullet would have less grease grooves than a heavy bullet too.)

All three of these things play an inseparable part in the final objective which is accuracy limited by the gun and the reloaders understanding of what is required for more. Are there more factors?

[felix]

Yep, baseball was my first love. Well, that sorta' petered out over the years after all the ******** and moaning. Nothing but a bunch of sissy movie stars anymore, with the same mental attributes, at least starting down that road. ... felix