RPM Test; a tale with three twists

[Larry Gibson]

Chapter 1; the test criteria

So why is it that when we push our cast bullet out of our accurate 30-06 we get very good accuracy at 1800 fps or so but when we push the bullet to 2100 fps we get pretty poor accuracy? Is there really an RPM threshold for cast bullets which establishes where the accuracy capability will deteriorate if the RPM threshold is exceeded? That seems to be the question. Just what do we mean by “RPM threshold”. The RPM threshold is that range of RPM where almost all cast bullets will lose accuracy if exceeded. For practical purposes when using a gas checked cast bullet with a BHN of 14-18 the RPM threshold is between 125,000 RPM and 140,000 RPM. But let us remember here that a “threshold is not a ‘limit’.

Thus those RPM threshold figures are not hard and fast as some things like a too soft alloy or too fast a powder can lower the threshold. Conversely, other things like a harder alloy or a slow burning powder can raise the threshold. However the RPM threshold is pretty consistent when we use cast bullets of designs that are readily available through commercial venders and are what most cast bullet shooters use. It is also these same designs that commercial bullet casters offer. Given a medium or slow burning powder we know that accuracy improves as the consistency of the internal ballistics improves. At a certain velocity accuracy begins to deteriorate. Since the RPM of a bullet is directly related to the twist (or show fast the bullet spins) of the barrel and the velocity at a certain point the RPM creating higher centrifugal force) overcomes the rotational stability of the bullet and accuracy decreases. The RPM threshold can be lower or the RPM threshold can be crossed into higher velocities if we use specialized cast bullet designs or tweak the loads in other ways. But for the most of us who use regular cast bullets the RPM threshold appears to be real and we need to understand it.

For a bullet to fly straight the center of form should coincide with the center of gravity and the center of spin must then coincide as closely to those as possible. When these centers do not coincide we have an unbalanced bullet that does not fly straight. A bullet thus imbalanced may wobble, it may yaw and/or its flight path may corkscrew around the intended flight path. The degree of these imbalances directly affects the accuracy or the ability to hit the same spot on the target. In basic terms an imbalanced bullet does not fly straight.

Can we demonstrate an increase in RPM above a certain threshold overcomes the rotational stability and decreases accuracy? Can we measure if and when bullets become more imbalanced? Will there be a direct correlation between measurements of imbalance and inaccuracy? All of these are good questions and the answer to all of them is yes. Let me explain but first I will describe the 3 test rifles.

All three rifles are chambered in .308 Winchester. All three are accurate with jacketed bullets and cast bullets. All three have free floated barrels. The three rifles have three different twists. The three test rifles used are; the 10” twist rifle is a M1909 Argentine Mauser with a 24” heavy sporter barrel. It has a Timny trigger set at 2 lbs. It has a 10X Weaver MicroTrac scope on it. This rifle is capable of consistent MOA accuracy with quality bullets. The 12” twist rifle is a M70 varmint rifle with heavy 26” barrel. The trigger is also set at 2 lbs. It has a 3x12 Redfield Ultimate scope on it. This M70 is capable of ½ MOA with match bullets. The 14” twist rifle is a M98 Mauser with a 27.5 barrel of Palma taper and weight. It too has a 2 lb trigger. This rifle has a 16X Weaver T16 on top. It is also capable of ½ MOA with match bullets.

What about the test loads? Well I will use the exact same loads in all three rifles. I will compare the accuracy of each rifle unto itself. In other words each rifle and it’s bullets flight will tell us when that rifles accuracy begins to deteriorate. The loads used in all three rifles will be the same and it is then when accuracy deteriorates in one rifle the RPM of that rifle with that load is comparable to the RPM of the same load in the other rifles.

Now to explain how we can measure if and when a bullet becomes imbalanced. I will use an Oehler M43 Personal Ballistics Laboratory to provide these measurements. The M43 will tell us the Time Of Flight and give us the Ballistic Coefficient of the bullet by measuring the muzzle velocity and the down range velocity. Along with the TOF and BC it will provide Standard Deviations and Extreme Spreads for these. A bullet that is not flying straight (imbalanced and inaccurate) will slow down quicker, have a lower BC and the SD/ES at the down range screens will be greater than that of a bullet that is flying straight (balanced and accurate). Thus if we have a bullet that is shooting accurately and as we increase velocity, with the attendant increase in RPM,
the accuracy decreases it tells us the increased centrifugal force of the higher RPM has overcome the rotational stability of the bullet and decreasing accuracy is the result. The M43 will also measure the chamber pressure of each round fired so we may compare how pressure may be affecting the bullet.

Now wait a minute you say, by increasing velocity we are increasing acceleration and the bullet is deforming in the bore through obturation and set back. That is the reason for the poor accuracy. Well that sometimes may be the case. However remember, we are using the same loads in each rifle so if the 10” twist rifle becomes inaccurate before the 12 and 14” twist rifles with the same load then we can assume it is the increased RPM of the 10” twist barrel is the culprit. Then if the 12” twist rifle also becomes inaccurate before the 14” twist rifle, all with the same load, then we have confirmed it is the increased RPM that is causing the inaccuracies.

To demonstrate the validity of these test methods a simple test was conducted with the 10” twist rifle. The M43 was set up with testing done at 100 yards. M118 Special Ball was used for the test. Now I think we can agree the 174 gr M118 bullet is not going to suffer any set back, bending, torque twisting or undue obturation during acceleration. At any rate, the test here is between regular M118 bullets and those I purposely unbalanced. If the regular M118 bullet suffers any of the mentioned deformations then the unbalanced M118 bullets would suffer the same deformations. So what we are testing is what the different effect of RPM will be on the balanced and unbalanced bullets.

This lot of M118 ammo, while 1.1 – 1.2 moa accurate in 12” and 14” twist barrels has not been much better than 2 moa in 10” twist barrels including M24 sniper rifles. And so it was with the M1909 with 10” twist. A ten shot string of regular M118 bullets was fired and they grouped right at 2 MOA. Then the ten shot string was then fired with the same lot (actually with the other 10 rounds out of the same 20 round box) of M118 that I had drilled a hole in the side to unbalance the bullet. I used a #31 drill and drilled the hole .06” deep removing 1.7 gr of the bullet in the side right in front of the case mouth. The M43 showed that the unbalanced bullets, when compared to the regular M118, averaged 5 fps faster MV, had a slower TOF, down range velocity was slower and had a lower BC. This is ample evidence the unbalanced bullets were not as stable in flight as the regular M118. The clincher was the group. The regular M118 grouped 2 MOA and the unbalanced M118 grouped into 6 MOA. Ample evidence of how the centrifugal force of the RPM affects the accuracy of unbalanced bullets. A picture of the two groups is attached.

How does this apply to cast bullets? Well most all cast bullets we cast are not perfectly round nor does the center of gravity coincide with the center of form. How much the cast bullet obturates, sets back, the nose bends to one side or the lube grooves collapse during acceleration depends on the hardness of the alloy and the fit to the throat. We should realize our beloved cast bullets for the most part are fairly unbalanced once they leave the muzzle. However with a normal alloy like WWS or #2 alloy GC’d cast bullets seem to withstand all this fairly well and given a reasonable fit to the throat they have good rotational stability and shoot accurately up to a certain point. It is at that point the centrifugal force of the RPM overcomes the rotational stability and the bullet shoots less accurately.

I intend to initially test two bullets; 311291 and 311466. Both will be cast from Lyman 2 cavity moulds. Alloy will be air cooled and the bullets have a BHN of 15-18. The gas checks will be Hornady’s and are seated with the Lyman 450 GC seater prior to sizing. The lube will be Javelina. Bullets will be sized in the Lyman 450 using a .311 H die. Powder will be H4895 with a ½ gr Dacron filler. Loads will work up in one gr increments from 26 to 36 grains. Cases are LC with the necks inside reamed with a Lee Target Loader for concentricity. All cases have been fire formed in their respective rifle and neck sized with a Forster/Bonanza Benchrest NS die. A Lyman .31 M die is used to expand the necks and flair the case mouths. The bullets are seated to just slightly engrave on the lands. Additional loads tested will be with two slow burning powders; RL19 and H4831SC.

Expected test velocities are expected to run from 1700 fps up through 2600 fps. Approximate RPM range of those velocities with each twist are:

10” twist; 122,500 – 187,000 RPM
12” twist; 102,000 – 156,000 RPM
14” twist: 87,500 - 134,000 RPM

When consistent high velocity loads (internally ballistic uniformity) are found additional tests will be conducted with the 10” twist rifle as it has the highest RPM potential. Those additional tests will be with different lubes (Lars), with the bullets water quenched out of the mould, will bullets cast of linotype and with bullets of various sizing (.311, .310, .309 and .308). Of course only one change will be tested at a time in an effort to see if the HV loads can be “tweaked”. I will even, to appease Bass, test with different barrel pressure.

Tests with the cast bullets will begin soon. Stay tuned for Chapter Two.

Larry Gibson

Addendum to Chapter 1; A picture of the two groups (regular M118 and unbalanced M118) are attached. Also, Glen's suggestion is an interesting thought. My thoughts on using a faster powder are since those who use the faster powders mostly use WWs that that would be the alloy to use. Just for sake of keeping it manageable three powders could be used, suggestions? I Could run that test at the conclusion of this test.

[dromia]

Many thanks for sharing this Larry, I'm looking forward to your results and any conclusions drawn.

[Johnw...ski]

Thanks Larry,

Your test should be very interesting and help address a point I tried and failed to make in my RPM thread, my feeling is that the slow twists advocated are so slow that by the time RPM problems arise other problems are well under way, such as leading.

The twist rates you are useing should help show that and would be even more telling in a larger caliber.

John

[Glen]

Excellent project! I look forward to reading your results. Have you considered adding a "fast" powder (e.g. 4198) to the list? Given the importance of how a bullet is introduced to the lands, this might prove enlightening.

[cbrick]

Fascinating larry, a lot of work just to do a post like that much less all of the testing.

I did a lot of BHN/accuracy testing "in revolvers" and it was apperant that a BHN spread "within the same group" did open up groups. As a SWAG the 15-18 BHN spread you mentioned could be enough in itself to open up groups at the higher velocities/RPM's, different BHN's would take the rifling differently. Not trying to be critical, just something for you to consider.

At any rate this will be a fascinating test series and everyone at Castboolits will benefit, much to be learned. Eagerly waiting the results and thanks for all the work.

Rick

[Larry Gibson]

......As a SWAG the 15-18 BHN spread you mentioned could be enough in itself to open up groups at the higher velocities/RPM's, different BHN's would take the rifling differently......... Rick

Rick

You are absolutely correct and I thoroughly expect the initial test will show that. What is going to happen is as we increase acceleration we are going to increase obturation, set back, nose bending and perhaps collapse of the lube grooves. All of these will increase the imbalances in the bullets and the RPM will have a greater affect, i.e. accuracy will get worse. The question we are answering with the three different twists is how much does RPM affect those imbalances. That is because we will be able to see the different accuracy effect each twist has on the same load at the close to same pressure and close to the same velocity. Point is; the RPM for that same load will be different because of the three different twists.

When we tweak the loads with harder bullets using the 10" twist rifle we will see how much we can lesson the adverse affect the RPM is having.

Larry Gibson

[Marlin Junky]

Larry,

How are you going to measure obturation, set back, nose bending and perhaps collapse of the lube grooves? Are you even going to have pressure equipment hooked up to the barrels with different twists?

MJ

[cbrick]

Point is; the RPM for that same load will be different because of the three different twists. Larry Gibson

Yes, of coarse it will. My point was simply that if the BHN varies 3-4 BHN within the same group of the same rifle that in itself will cause groups to open up and this could be confused with RPM as the cause.

Rick

[Larry Gibson]

Yes, of coarse it will. My point was simply that if the BHN varies 3-4 BHN within the same group of the same rifle that in itself will cause groups to open up and this could be confused with RPM as the cause.

Rick

Understood, and no problem with that. But again we are looking at 3 different levels of RPM with the same load. That same load should produce the same imbalances (averaged for the group) in all of the rifles as acceleration and velocity should be close. If the 10" twists accuracy decreases 50%, the 12" twists accuracy decreases 30% and the 14" twists accuracy decreases 15% with the same load at the same velocity and with the same pressure and thus with the same imbalances we then see the adverse effect the increased RPM of the 10" twist barrel has vs the 12 and 14" twist barrels.

Larry Gibson

[Larry Gibson]

Larry,

How are you going to measure obturation, set back, nose bending and perhaps collapse of the lube grooves? Are you even going to have pressure equipment hooked up to the barrels with different twists?

MJ

Yes, all three rifles will have the pressure testing equipment (the M43) attached to them. Actually they have it attached now. The pressure is measured in PSI and Dr. Oehler's very extensive test reveals the M43 PSI measurements to be very, very close to those of more sophisticated piezo conforming transducers used by the arms and ammunition industry. The M43 gives a graph showing the time pressure curve of each round fired and gives the area under the pressure curve from ignition to bullet exit. The peak rise is the time in micro-seconds from the 25% point to the 75% point indicating the burning rate of the powder.

The "obturation, set back, nose bending and perhaps collapse of the lube grooves' will not be measured per se. However, will be able to tell when those things happen to the bullet because the M43 will measure several things along with the chamber pressure; time of flight, Down Range Velocity, Ballistic Coeficeint and will give SD/ES for each. Decreases in the TOF, DRV and the BC along with increases in their SD/ES's tells us the bullet has deformed and is not flying straight. Or at least not as straight as it was with the accurate group. The size of those measurements will also indicate the degree the imbalance is affected by each RPM of a given load.

Remember also that each load is shot for group through the skyscreens during the test. So along with the pressure, TOF, DRV, BC and SD/ES we get the grouping of each shot with each load with each twist rifle. The M43 also gives ballistic tables for the load along with the recoil of the rifle.

Attached is a print out of the regular M118 test as mentioned in Chapter 1.

Larry Gibson

[44man]

I see a fly in the ointment! :mrgreen: First is using the same boolit for each twist. Right off the bat, the boolit might not be compatable with all three twists. In fact the weight, length and bearing surface of the boolit might only like ONE of the rates of twist. You will then lose accuracy in two of the rifles, perhaps very quickly.
We would be going not only into apples and oranges but also throwing peaches in.
Three different rifles with only one boolit??? What will be blamed for poor groups?
Excuse me if I am totally confused by this! :confused:
Let us say you have the perfect boolit for one of the twist rates and worked out a sub minute load for it. I can tell you just what would happen if you shot that same load from either of the other two rifles! :coffee:

[Bass Ackward]

You won't have the same pressure curve and the same acceleration in three rifles with the exact same twist.

And you certainly won't have the same pressure and acceleration with three different angles to forward motion. That is the same as having three different weight bullets. In fact, if you work up the max load in the slow twist, you will develop pressure problems as the twist rate increases eventually blowing the gun at some point if you had a fast enough twist cause eventually you would get to zero which is a blockage.

[felix]

John, the boolit would strip prior to the point of "blockage". If we would/could look at the boolits down range we could see the stripping action (if any) from the ogive to the base in a "Y" fashion where the tail of the "Y" would be at the boolit base (gas check area) assuming the lands finally grabbed hold at that point. If they never grabbed at all, then the boolit should be smooth showing no "Y" in the least bit. This experiment is interesting to say the least. ... felix

[Larry Gibson]

44man

Well, first of all I'm using two different bullets; one a bore rider (311291) which has been around for a hundred years or so and has proven to be accurate in many a 10 and 12" twist barrels of 30 caliber using many different cartridges. I have already found it to be accurate in the 12" twist M70, the 14" twist Palma and many other 10" twist barrels of .30 caliber. Besides there have been a lot of 32-40s with 14 and 16" twists that have been shooting cast bullets of that weight quite well for more than 100 years. I see no "fly in the ointment" there and think the 3 twists will do 311291 justice. But then I guess we'll see, wont we?

The second bullet is a Lovern design, 311466. Mine, with the alloy I'm usings weigh 159 gr all lubed and GC'd. Not only is the Lovern 311466 bullet renouned for accuracy potential at higher velocity but that weight bullet is quite compatable with all three barrel twists. But as with 311291 I guess we shall see.

However, if you caught what I said about the test; we will only compare the actual accuracy of each rifle to itself. In other words let's take 311291 and just for sake of argument say the accuracy with the 4895 powder at 1800 fps is 2" with the 10" twist, 1.4" with the 12" twist and 1.3" with the 14" twist. The TOF, DRV and BC variations are pretty close to each other for the three rifles. Then at 1900 fps the accuracy of the 10" twist opens to 2.5" but the 12" twist shoots .9" and the 14" twist shoots 1". The TOF, DRV and BC now are slightly greater for the 10" twist than with the other two twists. Then at 2200 fps the 10" twists group is 4.8", the 12" group is 1.1" and the 14" twist is .9". We also see from the TOF, DRV and BC that the 311291 bullet of the 10" twist is really unbalanced and not flying straight. The TOF, DRV and BC of the 12" twist 311291 is not as good as it was at 1900, 2000 and 2100 fps. The 14" twist 311291 however is showing the best TOF, DRV and BC that it has shown so far. What we are looking for here are trends. The trend this example shows us is that the 10" twist bullets accurate filght is being adversely affected by the RPM, the 12" twists bullet is begining to be adversly effected by the RPM and the 14" twists bullet is just doing fine. At 2200 fps the 10" twist bullet is doing 158,000 RPM, the 12" bullet is doing 132,000 RPM and the 14" twist bullet is doing 113,000 RPM.

Whether or not a trend of this type develops during the test to demonstrate the affects of RPM on a cast bullets accuracy remains to be seen. After all, that is why I am conducting the test.

Larry Gibson

[Larry Gibson]

I have edited this post to use reason with Bass instead of the previous flippant response.


Bass Ackward

"You won't have the same pressure curve and the same acceleration in three rifles with the exact same twist."

In fact you very seldom see the exactly the same pressure curve in the same rifle WITH the same ammunition. What we are going to see is average pressures with SDs and ESs just like velocities. If, over a 5 shot string, a load using 4895 under 311291 has an average peak pressure of 22,700 psi with an ES of 2,700 psi with a SD of 1,100 psi then that is pretty good. I'm certain of those as I've already been there. That load averaged 1761 fps out of the M70 with 12" twist and pretty good accuracy.
Let us consider "standards" of measuring accuracy, pressure and velocity. Lets say we take a box of 20 rounds of your best reloads with your LBT bullet and test them out of you '06 with a M$# (or any system that measures velocity, and pressure, even the most sophisticated systems a factory might have). We shoot them in four 5 shot strings at 100 yards from a solid bench. It is 70 degrees with 60% humidity, and no wind. We shoot these four 5 shot groups at 100 yards.

For accuracy we get four 5 shot groups measuring (ctc) .9, 1.1, .95 and 1.3 inches. So what can we say is the "accuracy" of the rifle with that load? Is it .9 or 1.3 inches? If it is .9 inches then are the other three wrong? No, none of them are wrong and we would average the four groups and say the rifle with that load was capable of 1.1 inch accuracy. That is an average and it is understood that not every group fired with that load in that rifle will be 1.1 inches.

When pressures are given (including the U.S. ammunition industry) for a load it is not stated as exactly 48, 268 psi or CUP is it? No it is not because it is well understood that with any lot of the same ammunition there will be a shot to shot variation. For the conditions we are testing your loads in an extreme spread of 5-7,000 psi for the 20 shots is within industry standard. The smallest measurement of psi is usually 100 psi but normally the industry uses 500 or 1,000 psi or CIP so we would more than likely see 48,268 listed as 48,000 or 48,500. Now with our test of four 5 shot strings of your load we find the average pressure (psi/m43) for each five shot string to be 42,100, 44,600, 41,800 and 43,500. What then is the correct pressure for your load? Is one of them right and the others wrong? Again, they are all "right" because they all fall within an acceptable ES of around 5,000 psi. We would probably average the 5 pressures and could then state with some certainty that that was the average pressure of that load under those conditions. We could further be a little more precise by giving the ES of the average pressure as a +/- figure.

Now let us look at the velocity of the four 5 shot groups; the first is 2497 fps with an ES of 46 and SD of 19, the second is 2501 fps with an ES of 51 and SD of 23, The third group is 2486 fps with an ES of 39 and an SD of 14 and the fifth group is 2494 fps with an ES of 44 and an SD of 18. So again we ask the question? Which is the right velocity? Again the answer is; they all are right. We would average the four velocities and say that that was the velocity of that load. We can also include the ES.

Would any of the measurements accuracy, pressure and velocity we finally arrive at be “exactly” correct? Probably not. But would we be wrong? No we wouldn’t because we could open another box of same load and test four more 5 shot strings and get four different answers again none of which would probably be the same as any of the first four answers. However they will be close to each other and we could state with reasonable correctness that that load is capable of a 1.1 inch accuracy at 100 yards with a velocity of 2490 fps and having a chamber pressure of 43,300 psi.

Are we “exactly” right? No but then we are not wrong either. That’s about as close as it gets. And it is exactly why we won't get the "exactly the same accuracy, exactly the same pressure curves, exactly the same feet per second velocity and exactly the same RPM out of the three rifles with different twists. However, the figures we do get will be within an acceptable ES of each other and will probably overlap the ES of the 5 shot test in each individual rifle. There is always some "variation" in every test. That variation will be taken into account. For example; we will be talking about RPMs in the hundreds of thousands and the RPM threshold itself has a spread of 15,000 RPM give or take. So is 1,000 or even 5,000 RPM difference between individual bullets going to skew the test results? Is a 3,000 psi difference in the pressure curve between the rifles going to skew the test results when there is 5,000 psi +/- ES for the same load in each rifle? Is a velocity difference of 100-500 fps going to skew the test results. No they are not because we are looking for trends not exactness.

"won't have the same pressure and acceleration with three different angles to forward motion."

I would disagree with you. So would many others. I refer you to the laws of physics; specifically that an object in motion tends to stay in motion. This includes rotational motion. Once the bullet has gone one length of the bullet at most it is all ready rotating in that direction. It appears that little or no further force is applied during acceleration from the angle of the twist. I would refer you to the excellent article in Lyman’s Cast Bullet Handbook, Third Edition, page 90 titled Technical Ramblings by Ken Mollohan. This is a reprint from the Cast Bullets Association’s Fouling Shot. In the article he refers to recover jacketed bullet that do not show any bearing (sliding marks) in the corners (he his talking about the rifling here). That is true. There is little evidence of pressure increasing due to the faster twists we are using. I will also refer you to Contractor Report ARAET-CR-04002, RIFILING PROFILE PUSH TESTS: AN ASSESSMENT OF BULLET, ENGRAVING FORCES INVARIOUS RIFLING DESIGNS where in it was found a bullet entering a leade of 2.5 degrees actually required less pressure to engrave than a bullet entering a 1.2 degree leade. You will also observe in that test how variations (ESs) of each sample and between different samples are expected and considered. However, we shall see from actual tests what the difference, if any, is.

I really hope we can keep this discussion reasonable and not go off on a tangent about some hypothetical way to creat such a fast twist that we blow rifles up. I am shooting 2 different bullets of designs that are and have been used for many, many years in the 3 different twists to be used in this test. Both the bullets and the twists of these barrels are well proven and we need not go off on a tangent. Let us stick with the task at hand.

Larry Gibson

[runfiverun]

hey larry
when the 10 fizzles here will you try adifferent powder and see if it will come back?
sounds like you expect it to be the first to go
same thing with the 12 ?

not trying to make this a four year project, but it would add some,..........
...? fire to the arguement.

[Bass Ackward]

Bass, if a dog had a square ass he could s**t bricks. I'm sorry about the abrupt comparison but for crying out loud, we are talking three barrel twists that have been sending bullets down range for over 130 years without the twist creating a blockage and blowing the gun up! But then you know the sun could go nova any time and we'd all be fried so why go on doing anything.....that makes just about as much sense. It is not the same as having three different bullet weights. It is having three different twists plain and simple. You might want to just sit back and see how the test turns out. You could be right couldnt you? "I'm feelin' the negative vibes..." Larry Gibson


Felix,

I was thinking copper here as most folks have worked maximums with copper that may be able to correlate. Another supporting point, how many 7 twist bolt rifles do we see in 22 caliber to shoot what is possible in a semi.


Larry,

No need to get uppity. Some folks here are really interested in this. Me too, just not in the narative. :grin:

Remember, the only reason for RPMs is to stabilize flight through .... air. Going to shoot this in a vacuum so we can see just RPM effects? So how good is it really? We already know that ol timers always said to use the slowest twist rate necessary for stabilized flight.

The difference between us is that we draw different conclusions as to why. If I can turn you around, look how it helps the board. So I am actually pulling for you here. Cause you have credibility.

Look, folks already know what each of us believes. If you read what you are writing here, you are sorta steering others (and yourself) for the outcome you expect. Keep an open mind cause it's a test right? You report, they'll decide. :grin:

One thing that you could do for me. We are all used to experiencing what a 30 MPH wind can do to our perfectly rotating, high velocity jacketed at 100 yards. Since I am a little slow at times, how about reporting your velocities in fps and MPH. I'll start you off, 2000 fps is 1468 MPH.

[45 2.1]

To demonstrate the validity of these test methods a simple test was conducted with the 10” twist rifle. The M43 was set up with testing done at 100 yards. M118 Special Ball was used for the test. Now I think we can agree the 174 gr M118 bullet is not going to suffer any set back, bending, torque twisting or undue obturation during acceleration.


Something to read about in regard to your assumption......
http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=A431357&Location=U2&doc=GetTRDoc.pdf (http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=A431357&Location=U2&doc=GetTRDoc.pdf)

[44man]

It will be interesting anyway.
What I haven't gotten clear is that if you take a certain boolit and work it in the 1 in 10" twist, then go to a slower twist, does it not need more velocity?
What I am reading here is that as the twist is sped up, the pressure and velocity will automatically increase. That would be the wrong direction as the faster twist calls for a lower velocity to start with.
If you work a load for maximum velocity in the 1 in 14" twist and then drop it in the 1 in 10" you will overspin the boolit and lose accuracy.
It still seems to me that each twist rate needs it's own load as does every different rifle with the same twist rate.
I still can't picture how shooting the same loads from a bunch of different twists and rifles is going to prove anything. The load will only be accurate in the rifle it was worked in.
Take 3 of the same rifles off the assembly line and shoot the same loads and you will have 3 different group sizes. They might be close, but not the same. There is even a chance that 1 of those will not shoot a cast boolit no matter what you do.

[Larry Gibson]

hey larry
when the 10 fizzles here will you try adifferent powder and see if it will come back?
sounds like you expect it to be the first to go
same thing with the 12 ?

not trying to make this a four year project, but it would add some,..........
...? fire to the arguement.

Based on 40+ years of shooting and cast bullets and observing how cast bullets shoot in 10, 12 and 14" twist barrels (also faster and slower twist barrels) I do believe the 10" barrel will loose accuracy first and be followed by the 12" barrel.

This shouldn't be a 4 year project and I expect to have it completed not later than mid summer. What's holding me back is the cold weather (what happened to Gore's "global warming").

Actually I'll be using 3 powders in the test; H4895, RL19 and H4831SC. Those pretty much take the .308 case from 60% loading density to 100% loading density. Plus with the slower powders the velocity level attainable might not produce sufficient RPM from the 14" twist. I will, to appease Bass, then switch to my 10" twist 30-06 for more case capacity with the slow powders. I will use both bullets in this test and the last of Bass's 154 gr LBT bullets he sent me. I expect to use RL15, RL19 and H4831SC in tose tests.

Larry Gibson

[Larry Gibson]

Bass

Sorry about the "uppity", I deleted it before I saw this post. You might read what I replaced it with.

"Remember, the only reason for RPMs is to stabilize flight through .... air."

Not quite right. The reason for RPM is to stabilize period. Objects in space will tumble if not rotaing around an axis for stabilization. Basic physics.

"Going to shoot this in a vacuum so we can see just RPM effects? So how good is it really?"

Another tangent, no need for the vacuum as we don't shoot cast bullets that way here on Earth. We shoot them through air so that's how I'll test them. We shall see the effects of RPM just as I explained it.

"We already know that ol timers always said to use the slowest twist rate necessary for stabilized flight."

Bass, if YOU believe the old timers then you already know I am right.


"The difference between us is that we draw different conclusions as to why. If I can turn you around, look how it helps the board. So I am actually pulling for you here. Cause you have credibility."

To "turn me around" is an assumption that I am wrong. I do not believe I am wrong so me turnin' around ain't going to happen. Although, perhaps one of us will turn around at the conclusion of these tests. Thank you for your confidence.

"Look, folks already know what each of us believes. If you read what you are writing here, you are sorta steering others (and yourself) for the outcome you expect. Keep an open mind cause it's a test right? You report, they'll decide. :grin:"

The example given was not an attempt to steer anyone anywhere, it was an answer to a question. The results will speak for themselves. As I stated earlier; you could be right! :)

"One thing that you could do for me. We are all used to experiencing what a 30 MPH wind can do to our perfectly rotating, high velocity jacketed at 100 yards. Since I am a little slow at times, how about reporting your velocities in fps and MPH. I'll start you off, 2000 fps is 1468 MPH."

MPH? Bass, I'm kind of doing enough here. I really don't see any need for MPH as no one in the sport, hobby or industry is listing velocity that way. Besides, or perhaps you've forgotten this test is about the effects of RPM on cast bullets. You are not really slow so if you want MPH feel free to make the conversion, sorry.

Larry Gibson

[Larry Gibson]

44man

"What I haven't gotten clear is that if you take a certain boolit and work it in the 1 in 10" twist, then go to a slower twist, does it not need more velocity?"

To equal the same RPM as the 10" twist yes.

"What I am reading here is that as the twist is sped up, the pressure and velocity will automatically increase. That would be the wrong direction as the faster twist calls for a lower velocity to start with."

That Pressure and velocity speed up "automaticaly" is an assumption that will be answered by the test. Bass thinks it does, there are others who think it doesn't. We shall see.

"If you work a load for maximum velocity in the 1 in 14" twist and then drop it in the 1 in 10" you will overspin the boolit and lose accuracy."

Seems as though you've a good understanding of the effects RPM has on cast bullets.

"It still seems to me that each twist rate needs it's own load as does every different rifle with the same twist rate."

That is true if we are looking for the best accuracy from a specific rifle with a specific bullet. However we are not looking for "best accuracy" in this test. We are looking for comparative accuracy. In other words we want to simple find how accurate each rifle shoots the same bullet. That one rifle shoots that bullet more accurately doesn't matter. What we want to find is when (velocity/RPM) that accuracy gets worse in that rifle. It is the velocity level (tells us the RPM) where accuracy gets worse in each rifle that we compare.

"I still can't picture how shooting the same loads from a bunch of different twists and rifles is going to prove anything. The load will only be accurate in the rifle it was worked in.

Take 3 of the same rifles off the assembly line and shoot the same loads and you will have 3 different group sizes. They might be close, but not the same. There is even a chance that 1 of those will not shoot a cast boolit no matter what you do."

Again, we are not comparing the accuracy of the rifles to each other. we are looking for the velocity level at which each of them looses accuracy. Say two of the rifles best accuracy is 2 MOA and one of them only shoots 4 MOA. That's ok for this test. What we want to find is at what velocity the two 2 MOA shooters start shooting 2+ MOA and at what velocity the 4 MOA rilfe starts shooting 4+ MOA.


Larry Gibson

[Larry Gibson]

Something to read about in regard to your assumption......
http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=A431357&Location=U2&doc=GetTRDoc.pdf (http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=A431357&Location=U2&doc=GetTRDoc.pdf)

I already have that document and have studied it. I also suggested to Bass that he read it. Did you note that the lead projectile took very little force to engrave?What is your point in relation to my assumption?

Larry Gibson

[45 2.1]

I already have that document and have studied it. I also suggested to Bass that he read it. Did you note that the lead projectile took very little force to engrave?What is your point in relation to my assumption?

Larry Gibson


It has to do with this part of your post:

Now I think we can agree the 174 gr M118 bullet is not going to suffer any set back, bending, torque twisting or undue obturation during acceleration.

In the article, pay attention to the forcing cone data and how even jacketed and solid copper bullet can go through a plastic stage during forcing cone/bore transition.

You also posted:

This lot of M118 ammo, while 1.1 – 1.2 moa accurate in 12” and 14” twist barrels has not been much better than 2 moa in 10” twist barrels including M24 sniper rifles. And so it was with the M1909 with 10” twist. A ten shot string of regular M118 bullets was fired and they grouped right at 2 MOA. Then the ten shot string was then fired with the same lot (actually with the other 10 rounds out of the same 20 round box) of M118 that I had drilled a hole in the side to unbalance the bullet. I used a #31 drill and drilled the hole .06” deep removing 1.7 gr of the bullet in the side right in front of the case mouth. The M43 showed that the unbalanced bullets, when compared to the regular M118, averaged 5 fps faster MV, had a slower TOF, down range velocity was slower and had a lower BC. This is ample evidence the unbalanced bullets were not as stable in flight as the regular M118. The clincher was the group. The regular M118 grouped 2 MOA and the unbalanced M118 grouped into 6 MOA. Ample evidence of how the centrifugal force of the RPM affects the accuracy of unbalanced bullets.

This test was conducted with cast boolits also and written up in Handloader or Rifle article some years previous. The results as you found were such when the boolits were not oriented, but they did shoot just slightly larger groups (nothing on the order of 3 times as large) when the drilled holes were oriented in the same position in the chamber. I think your analysis should include oriented in relation to defect groups for your jacketed trials also to prove non-skewing of data and results, since your statement has already been carried out with cast showing different results.

[pdawg_shooter]

If RPM causes the problems, why can I shoot pure lead with 2% tin added at 2200fps accurately when I wrap the bullet in paper? I have also taken linotype 152gr 30cal to over 3500fps in a 300RUM with no problems.

[felix]

PS, paper increases friction, as does lino and copper. Friction is your friend when it comes to rotating something with a force applied at a 90 degree angle to the direction of the rotation. ... felix

[Larry Gibson]

If RPM causes the problems, why can I shoot pure lead with 2% tin added at 2200fps accurately when I wrap the bullet in paper? I have also taken linotype 152gr 30cal to over 3500fps in a 300RUM with no problems.

Pdowg

So ok that is 2200 fps at what RPM, or with what twist? The paper patch is just like a jacket as it protects and supports the bullet from nasty things happening in the bore during accelleration. Thus it is not nearly as unbalanced and thus the RPM doesn't effect it as much. If your rifle has a 12" twist then the RPM is 132,000 right in the middle of the RPM threshold and it should shoot accurately. If the twist is a 10" then let me ask if the accuracy is not better down around 1800-1900 fps? If the twist is slower than 12" then you've not been paying attention.

As to the 300 RUM; what do you mean by "no problems"? The question pdawg is not how fast we "can" drive a cast bullet. We know we can drive them fast. The question is at what RPM do we begin to loose accuracy. What kind of accuracy did you get at said 3500+ fps with the cast bullet? Was accuracy better down in the 1800-1900 fps range?

Larry Gibson

[Larry Gibson]

45 2.1

“It has to do with this part of your post:

Now I think we can agree the 174 gr M118 bullet is not going to suffer any set back, bending, torque twisting or undue obturation during acceleration.

In the article, pay attention to the forcing cone data and how even jacketed and solid copper bullet can go through a plastic stage during forcing cone/bore transition.”

This is what it says in the conclusion of the report;
“3. A slight decrease in resistance force was observed for the 2.5 deg half angle forcing cone
compared to the 1.2 deg half angle forcing cone found on the M240 barrel baseline. It is
believed this difference is due to a reduction in the plastic deformation of the M80
projectile in the 1.2 deg barrel.”

If you go back and read the report you will find that the term “plastic deformation” is the engraving of the bullet by the rifling. The report says nothing about, nor does it address, obturation. The machine used to measure the force required for the bullet to enter the barrel over the forcing cone of the leade in no way developed the pressures made during firing a round. I suggest you reread the report.

I will also refer you to the Technical Ramblings article in the Lyman Cast Bullet Handbook. As mentioned in the article, I’m sure you, I and most everyone reading this has picked up jacketed bullets down range. None of them have exhibited any deformation from any obturation, twisting or bending in the bore, have they. We also have recovered many bullets that except for the rifling engraving could be loaded and fired again. Many, many jacketed bullets will not even expand (that’s obturate) into the lands and show no marks of riding that part of the barrel. We also know that shooting undersized jacketed bullets in barrels (.308 bullets in .310-.312 barrels for instance) is not conducive to any accuracy because the bullet does not obdurate. So what is your point?

“This test was conducted with cast boolits also and written up in Handloader or Rifle article some years previous. The results as you found were such when the boolits were not oriented, but they did shoot just slightly larger groups (nothing on the order of 3 times as large) when the drilled holes were oriented in the same position in the chamber. I think your analysis should include oriented in relation to defect groups for your jacketed trials also to prove non-skewing of data and results, since your statement has already been carried out with cast showing different results.”

I think you should run your own test and post the results. I really don’t think most shooters orient the bullets of either jacketed bullets or cast bullets when testing for accuracy do they? And just to remind you, I am not conducting this test to find the most accurate loads. I am conducting this test to find the effects of RPM on the accuracy (regardless of how good it is) of cast bullets.

Larry Gibson

[45 2.1]

Hmmm..... You should let everyone else decide what the results of your "tests" are, otherwise you are just feeding them what you want them to think. I am posting what other people have found and written in published material. And Yes, several disciplines use oriented or aligned methods of chambering a cartridge when shooting. I'm quite suprised that you would even say that.

[felix]

Larry, it's obTurate, not obDurate. Some spell checkers are confused because they don't carry both words. ... felix

[Larry Gibson]

Hmmm..... You should let everyone else decide what the results of your "tests" are, otherwise you are just feeding them what you want them to think. I am posting what other people have found and written in published material. And Yes, several disciplines use oriented or aligned methods of chambering a cartridge when shooting. I'm quite suprised that you would even say that.

Yes 45 2.1 several "disciplines' do orient the bullets. But just how many of those disciplines shoot a 311291 out of the hunting 10" twist '06? Not very damn many right. Fact the vast majority of cast bullet shooters do not orient thier bullets. But they do want to know why the accuracy of cast bullets goes to crap above a certan point. That's what were talking ablout.

Thank you BTW; has it occured to you that orienting the bullets is simply a way of consistantly putting the defects of the bullet in the same location regards the bullets exit from the muzzle so that the RPM effects the flight of the bullet the same way? Well if it hasn't occured to you then it should because that is what the article in Handloader was about; negating the effects of RPM by locating the bullets defects in the same place. So we are in agreement then that RPM does have a negative effect on cast bullets?

Again let me remind you that the point IS NOT to find the most accurate load. The test is simply to find out how and when RPM adversely affects the accuracy of a cast bullet. It does not matter whether the best accuracy is 1 MOA or 2 MOA. What does matter is when that accuracy of 1 or 2 or whatever MOA gets worse. Is this really that hard for you to understand or do you just want to argue something before the test is completed.?

BTW; If you'll take a look at the rifling engraving test you brought up to me and go the end you'll find something called a "conclusion". In case you don't know, the person(s) conducting such tests always give a conclusion. The conclusion is thier observations of what they observed (makes sense since they conducted the tests) and thier answers to a, or any, questions or assumptions. Most tests are conducted to answer questions or assumptions aren't they. In other words, yes I will draw my own conclusions regarding the results of the test which I am conducting. That is normal for a test of this nature. Whether anyone else agrees or disagrees is up to them. I am not conducting a test seeking a consensu of agreement. I am looking for facts.

However isn't it a little futile for you to disagree about the results and what I may or may not do with them when the test hasn't even been conducted with cast bullets yet? Haven't you got the cart before the horse here? I'm sure you will disagree. I expect it. You always disagree. That's ok as we can discuss it, or disagree about it, when the test is complete. But as I suggested; perhaps if you ran a test or two yourself then maybe we'd have a basis for disagreement.

Larry Gibson

[Larry Gibson]

Larry, it's obTurate, not obDurate. Some spell checkers are confused because they don't carry both words. ... felix

Thank you felix, I didn't catch that one. My bad as I do know it is "obturate". When I learned to type in high school there was 3 guys and 30+ girls in typing class, guess I should have paid more attention to the keyboard!

Larry Gibson

[45 2.1]

Yes 45 2.1 several "disciplines' do orient the bullets. But just how many of those disciplines shoot a 311291 out of the hunting 10" twist '06? Not very damn many right. Such language! Only the disciplines (which there aren't many of to begin with) that have classes in that catagory, the CBA for one. Others that orient might be the long range BP shooters, but they don't shoot that caliber of rifle. Only Steve Garbe has published shooting cast with BP in a 30 caliber in a nationally published magazine that I know of. Fact the vast majority of cast bullet shooters do not orient thier bullets. Most of those don't shoot groups on paper either. But they do want to know why the accuracy of cast bullets goes to crap above a certan point. That's what were talking ablout. Or trying to at least.

Thank you BTW; has it occured to you that orienting the bullets is simply a way of cosistantly putting the defects of the bullet in the same location regards the bullets exit from the muzzle so that the RPM effects the flight of the bullet the same way? Well if it hasn't occured to you then it should because that is what the article in Handloader was about; negating the effects of RPM by locating the bullets defects in the same place. You seem to be saying that RPM effect, as you put it, can be negated by useing boolits that have no defects in them or by locating them in the same place, IS THAT CORRECT? If so then you can stop your tests and simply use boolits with no defects in them or orient. To that end, since you say that a vast majority of shooters don't orient, you should find someone to give lessons in casting good boolits to everybody. Again let me remind you that the point IS NOT to find the most accurate load. I haven't said a thing about accuracy in this thread at all. You must be confusing me with someone else. The test is simply to find out how and when RPM adversely affects the accuracy of a cast bullet. Again, that would be a defective cast boolit as you thanked me for above? It does not matter whether the best accuracy is 1 MOA or 2 MOA. What does matter is when that accuracy of 1 or 2 or whatever MOA gets worse. If it doesn't matter how it shoots, just how much above the group range are you going to use to determine when that happens. Is this really that hard for you to understand or do you just want to argue something before the test is completed.? I'm trying to figure out your changing parameters. Please state what controls your going to use. Not general ones either.

That's ok as we can discuss it, or disagree about it, when the test is complete. So, work on completeing the test. All this time wasted on talk. :mrgreen:

[carpetman]

Larry Gibson--If we are correcting spelling--it's consistently not consistantly. People are pretty consistent at using an A but there isnt one in the word.

[Larry Gibson]

45 2.1

"Please state what controls your going to use."

Go to first post that started this thread and read carefully. The specific controls are there.

Do you cast perfect bullets? Then why would you orient them then? BTW; no bullet is perfect, especially after it comes out of the barrel. That's why we our bullets go into "groups" instead of one hole every time. But I've really got to ask; are you a lawyer? I ask this because your arguement technique is just like the old lawyer trick; if you cant win the case with facts attack the credibility of the witness. And yes you have wasted a lot of my time with this "talk". Thus I will ignore the rest of your comments.

Larry Gibson

[Larry Gibson]

Larry Gibson--If we are correcting spelling--it's consistently not consistantly. People are pretty consistent at using an A but there isnt one in the word.

Perhaps you are asking this of felix? He is the one correcting spelling. I'm assuming I'm the only one who's ever mispelled a word on this forum?

Larry Gibson

[45 2.1]

Do you cast perfect bullets? Ahh...., Larry, I don't cast bullets. I cast boolits. Here is what 45 nut has posted about this;

Boolits= as God laid it into the soil,,grand old Galena,the Silver Stream graciously hand poured into molds for our consumption.

Bullets= Machine made utilizing Full Length Gas Checks as to provide projectiles for the masses.

Seems to be a good description to me and others.

Then why would you orient them then? Some fella named Dave Farmer made me a mold that requires that. A 45 caliber 420 gr. one that will make one hole groups at 100 yards when you do orient them.

BTW; no bullet is perfect, especially after it comes out of the barrel. Those FLGC jobs do seem to do that.

That's why we our bullets go into "groups" instead of one hole every time. I know several fellas that shoot bullets into one hole groups. They have to buy those bullets, but they do shoot well. This last summer four of us shot one rifle at 300 measured yards. It was a Browning 308 bolt gun with a boss on it with match grade loads. The owner, his buddy, me and castalot all shot 3 shot groups of 1/2" at 300 yards with it. Witnessed by about 7 people.

But I've really got to ask; are you a lawyer? My profession is in my profile, all you need to do is look. I ask this because your arguement technique is just like the old lawyer trick; if you cant win the case with facts attack the credibility of the witness.
I don't write your stuff, you do. All I did is compare your results with published articles.

And yes you have wasted a lot of my time with this "talk". Thus I will ignore the rest of your comments. That's about what I expected you to do. Since you have time now, get on with it and see what you come up with.

[felix]

Nah, Larry, the C-Man is looking for stray cats. Well, maybe he has me in his sights just as you suggested. Anyroad, mispeling is notricias on this borde. It hurts only when the misspelled word means another legit word. ... felix

Oh, he missed one: their is not equal to thier, there. But, the converse is true in the spirit of the board.

[Larry Gibson]

Nah, Larry, the C-Man is looking for stray cats. Well, maybe he has me in his sights just as you suggested. Anyroad, mispeling is notricias on this borde. It hurts only when the misspelled word means another legit word. ... felix

Oh, he missed one: their is not equal to thier, there. But, the converse is true in the spirit of the board.

Thanks felix

I shall endeavor to persevere. Or is it “persevere to endeavor”?

Larry Gibson

[carpetman]

Larry Gibson---There was no question. My statement was not directed at felix as he was not the one that had spelled consistently "consistantly". You were gracious and receptive to the other correction,so I pointed this out as I do think you aspire to do writing as evidenced by a story I read that was written by you.

[Larry Gibson]

Larry Gibson---There was no question. My statement was not directed at felix as he was not the one that had spelled consistently "consistantly". You were gracious and receptive to the other correction,so I pointed this out as I do think you aspire to do writing as evidenced by a story I read that was written by you.

Sorry if I gave you the wrong impression. I do usually use spell check or proof read. However occasionally one gets buy me. I occasionally write and try to use proper English and grammer. I appreciate the correction actually. Thank you.

Larry Gibson

[carpetman]

Larry Gibson--LOL Was this a test? I think so. One gets "buy" me. Are you on the auction? You use proper grammer---is that on your mom or dad's side? GRAMMAR.

[Larry Gibson]

Larry Gibson--LOL Was this a test? I think so. One gets "buy" me. Are you on the auction? You use proper grammer---is that on your mom or dad's side? GRAMMAR.

You passed! I was just trying to add some levity here.

Larry Gibson

[Marlin Junky]

Larry,

I couldn't care less about who's the reining spelling-bee champ, but I would like to know more about your rate of twist experiment. How are you controlling groove depth, etc? In other words, are all the barrels virtually indentical except for rate of twist? What alloys are you going to compare? I assume you're going to use the same bullet mold throughout the entire experiment... which one would that be?

MJ

[Larry Gibson]

Larry,

I couldn't care less about who's the reining spelling-bee champ, but I would like to know more about your rate of twist experiment. How are you controlling groove depth, etc? In other words, are all the barrels virtually indentical except for rate of twist? What alloys are you going to compare? I assume you're going to use the same bullet mold throughout the entire experiment... which one would that be?

MJ

Marlin Junky

Most of the answers to your questions are in the first post of this thread.

No, the barrels are not identical. They do not have to be as I am not attempting to show one rate of twist is more accurate than another. I am attempting to demonstrate at what velocity the accuracy of each particular rifle falls off. Knowing what this velocity is, along with all of the other things as explained in the first post, will tell us if, when using a slower twist barrel for a given cartridge, we may get a higher velocity before accuracy falls off. If the accuracy falls off at close to the same RPM for each barrel then that confirms it is the RPM causing the inaccuracy. I will be measuring the muzzle velocity, the down range velocity, the time of flight, the BC and the chamber pressure on each shot fired.

Given the same load in each rifle a slower down range velocity, a slower time of flight and a lower BC in one rifle but not the others gives evidence the bullet is not as stable in flight and that RPM is adversely affecting that bullet out of that rifle. Of course one will also expect with these lower readings that the group will open, i.e. the accuracy falls off. Given the same load(s) fired in each rifle the pressure curves and the rise in microseconds should be close or within acceptable shot to shot variation. Given that the pressure readings are close together for a load then any adverse effects on the bullet from acceleration should be relatively equal in all three barrels.

We may then deduce, if accuracy falls off in the quicker twist barrels first, that the increased RPM of the faster twist barrel is overcoming the rotational stability of the bullet before the slower twist barrels are, hence they produce slower RPM, . However, if accuracy falls off pretty much at the same velocity in all three barrels then we may deduce that pressure (remember the pressures of each shot will be taken) then is the culprit. We will have ruled out RPM because the RPM at the same velocity will be considerably different because of the three different twists of the barrels.

Larry Gibson

[pdawg_shooter]

Pdowg

So ok that is 2200 fps at what RPM, or with what twist? The paper patch is just like a jacket as it protects and supports the bullet from nasty things happening in the bore during accelleration. Thus it is not nearly as unbalanced and thus the RPM doesn't effect it as much. If your rifle has a 12" twist then the RPM is 132,000 right in the middle of the RPM threshold and it should shoot accurately. If the twist is a 10" then let me ask if the accuracy is not better down around 1800-1900 fps? If the twist is slower than 12" then you've not been paying attention.

As to the 300 RUM; what do you mean by "no problems"? The question pdawg is not how fast we "can" drive a cast bullet. We know we can drive them fast. The question is at what RPM do we begin to loose accuracy. What kind of accuracy did you get at said 3500+ fps with the cast bullet? Was accuracy better down in the 1800-1900 fps range?

Larry Gibson
The RUM groups were 1.2 to 1.85 five shot over about 40 or more tries.

[Pat I.]

Larry, You might not know it but there are people out here that understand what you're doing.

[Marlin Junky]

Larry,

I don't see how you can ignore groove depth and be able formula any axioms that relate to twist rate.

MJ

[Larry Gibson]

The RUM groups were 1.2 to 1.85 five shot over about 40 or more tries.

40 or more tries...hmmmm.... can you now do that consistantly? If not then let us remember something about the laws of probability and monkeys. It goes something like this; if enough monkeys beats on typewriters long enough one will type the word GOD. If those groups are repeatable I am very interested in learning what you do.

Larry Gibson

[Larry Gibson]

Larry, You might not know it but there are people out here that understand what you're doing.

Thanks Pat, I know that. I've recieved numerous PMs. I shall endevor to persevere.

Larry Gibson

[Larry Gibson]

Larry,

I don't see how you can ignore groove depth and be able formula any axioms that relate to twist rate.

MJ

Perhaps it shouldn't be ignored. I really did not think it pertinent. Could you elucidate how groove depth relates to the effect RPM has on a bullet in flight?

Larry Gibson

[felix]

Larry, I am beginning to think the terms endeavor and persevere should be reversed. Why? Because of all of the flack from all corners around here, your whole being (physically, emotionally, intellectually,spiritually) must persevere to endure this endeavor to its completion. (((Notice the spelling of endeavor before the C-man gets you! Again!!!))) ... felix

[Larry Gibson]

Larry, I am beginning to think the terms endeavor and persevere should be reversed. Why? Because of all of the flack from all corners around here, your whole being (physically, emotionally, intellectually,spiritually) must persevere to endure this endeavor to its completion. (((Notice the spelling of endeavor before the C-man gets you! Again!!!))) ... felix

LOLs felix

I shall persevere in that case. I really appreciate the PMs, along with your post and Pat I's and others as they tell me support is there. Obviously the nay sayers are out in full force attempting to discredit a test that has even been done yet. After all I could be wrong eh? But I really don't think so. The nay sayers kind of remind me of a Shakespeare line' "me think thou does't protest to much". In other words it appears they worry their pet ideas and opinions might be wrong. Me? I don't worry about it. If I'm wrong then we learn from it. If I'm right then we advance our knowledge of shooting cast boolets. Perhaps my attitude is askew. If it is, then so be it.

Larry Gibson

[felix]

Larry, it makes no difference if you are right or wrong. It should be a fun thing, and when it isn't at any time, just provide a bunch of misspelled words in/with your resignation. We will all understand. ... felix

[runfiverun]

larry

i know you have put a LOT of thought and effort into this.
and as you are changing variables and keeping the same baseline here
i would call this a very viable experiment.

even if you cut the bbl's yourself they would not be the same.

so ta got what ya got, let's see what ya get.

appreciate your efforts here,
Lamar

[Marlin Junky]

Perhaps it shouldn't be ignored. I really did not think it pertinent. Could you elucidate how groove depth relates to the effect RPM has on a bullet in flight?

Larry Gibson

Larry,

First of all I can't believe I banged out such a poor sentence! It should have read:

I don't see how you can ignore groove depth and be able to formulate any axioms that relate to twist rate.

The reason I would hold groove depth constant is because shallow grooves will strip the bullet before deeper grooves as pressure and velocity increase. That's pretty basic, isn't it?

MJ

[44man]

I understand completely what Larry is trying to do, however he is missing the point! [smilie=1:
The point being that one or two boolits tested in different twists will not tell the whole story. To be valid, each twist should be tested with the whole range of boolit weights in EACH gun to establish the twist limit FOR EACH BOOLIT.
In other words the range for say a 30-06, should include weights from 125 to 220 gr's and the point of accuracy loss recorded for each. Now we would have a usable chart for each twist rate.
We have to overlook the difference in alloys and boolit design because just a baseline would be the goal. ( The occasional flier should be left out too.)
To use one or two weights will show an extreme accuracy loss long before the actual loss of usefulness of a twist rate for cast boolits is reached. All we would learn is that one boolit can't be shot that fast.
I don't want to see everyone say that a certain twist is no good for cast based on tests done with one boolit. Every twist we have will shoot SOMETHING at some velocity. (Except some Marlins :mrgreen:)
What is needed is to show where EACH boolit goes to pot and the RPM's reached. Then you could try and figure the velocity needed for that boolit in a different twist rate.
To do it right would take more resources then any of us has. :Fire:
But when all is said and done, what Larry finds will add to knowledge with lead and RPM's but will not aid in choosing a boolit for a rifle that someone wants to shoot fast.
Maybe I am completely missing Larry's point though! :confused:

[Bass Ackward]

Larry,

<<Is a 3,000 psi difference in the pressure curve between the rifles going to skew the test results when there is 5,000 psi +/- ES for the same load in each rifle? Is a velocity difference of 100-500 fps going to skew the test results. No they are not because we are looking for trends not exactness.>>


This is the fundamental difference between us. And apparently the key to my success.


I had an epiphany! I always wanted to be able to say that. Won't tell you where this occurred either as this is a family friendly site. :grin:

Say for a second I am WRONG. RPMs can't be the reason either. And I will put forth the logic.

We know that RPMs of a bullet slow very little over a bullets flight. You have stated this before. Do you agree? Has anyone read of a test where this has been proven fact?

Once a bullet is unbalanced and leaves the bore that way, it will remain unbalanced until it contacts earth.

If "Over RPMs" were the cause of wobble of an unbalanced bullet, then that bullet would be wobbling all the way to the target. A "permanent condition of flight" because balance will not change after launch. And rotation will not slow. Sound logical?

All of the holes in any target, at any range, of an unbalanced slug that is over RPM'd would have to be oblong until that slug contacts earth. If "over RPMs" was the cause..

OR .... then the theory about RPMs not slowing down would have to be wrong. Can't have it both ways with Physics.

BUT ............ if the holes are round, then RPMs turned out to be my correcting friend .... and stabilized flight eventually occured. The key being how long the unstabilized slug was exposed to air before it stabilized and how fast (velocity) of the headwind was. In other wordes, the faster you drove it, the crappier groups got. And we do know that velocity is directly proportional to pressure.

Another point is that twist rate makes fixed number of RPMs unless velocity is increased. As velocity increases, time of flight goes down. The bullet actually rotates LESS to the larget as you go faster. So higher RPMs actually occur as it slows down.



Was that good or what? I just saved you all that time and money testing. :grin:

[felix]

Well, John, let's just say the ellipses (holes) must have the major axis in the same direction, AND in the direction of the wind. If no wind, then the holes must be round for the testing to be kosher. ... felix

[Bass Ackward]

Well, John, let's just say the ellipses (holes) must have the major axis in the same direction, AND in the direction of the wind. If no wind, then the holes must be round for the testing to be kosher. ... felix

OK. Then that's going to sleep and that says that it isn't over RPMs. Right?

If all velocity remained the same upon bullet exit and velocity was not altered by the wobble, then the axisa should be the same. But any variance, and they would be going different directions?

The only variables being BC and velocity and outta balance. Outta balance is a constant once happened, velocity and the resulting RPM change the only flux. So it would still fly like a football correct?

[Larry Gibson]

Larry,

First of all I can't believe I banged out such a poor sentence! It should have read:

I don't see how you can ignore groove depth and be able to formulate any axioms that relate to twist rate.

The reason I would hold groove depth constant is because shallow grooves will strip the bullet before deeper grooves as pressure and velocity increase. That's pretty basic, isn't it?

MJ

Now I understand, you are correct. The M70 and M90 Palma both have about .004" groove depth. Three lead slugs averaged .3082 x .3001" for both of those barrels. They are both 4 groove barrels. The new 10" twist barrel is a little tighter at .3081 x .2998" average for 3 slugs and has a .004" groove depth also. It is however a 6 groove barrel. Any opinions on the 4 vs 6 grooves?

Larry Gibson

[felix]

Six grooves will give more bite which translates into more beneficial friction up front when the lands having the same vertical height. However, angled lands clean better overall while shooting and also when ramrodded, but angled lands also provide more possibility for rotational slippage. I think John (BA) ran into this syndrome having a custom barrel made up with stronger than normal angles. So, the results on target are still non-predictable unless the barrels are exactly the same in all other respects, like smoothness, leade-in, land-groove ratio, etc. Who knows, in other words. This experiment is going to be fun to watch, much like Joeb's experiment with various powder displacements. ... felix

[Larry Gibson]

44man

"The point being that one or two boolits tested in different twists will not tell the whole story. To be valid, each twist should be tested with the whole range of boolit weights in EACH gun to establish the twist limit FOR EACH BOOLIT.
In other words the range for say a 30-06, should include weights from 125 to 220 gr's and the point of accuracy loss recorded for each. Now we would have a usable chart for each twist rate."

"To do it right would take more resources then any of us has."

You answer your own postulation. That would be a very daunting and expensive task.

"To use one or two weights will show an extreme accuracy loss long before the actual loss of usefulness of a twist rate for cast boolits is reached. All we would learn is that one boolit can't be shot that fast. I don't want to see everyone say that a certain twist is no good for cast based on tests done with one boolit. Every twist we have will shoot SOMETHING at some velocity. (Except some Marlins :mrgreen:)
What is needed is to show where EACH boolit goes to pot and the RPM's reached. Then you could try and figure the velocity needed for that boolit in a different twist rate. "

It is my experience and observation that there is no exact velocity (RPM) where a bullet will go to pot in every rifle of a particular twist. We know that each rifle barrel is slightly different. We know there are variances in alloys, lubes, powder burning rates, etc. that all have an effect. It is also my experience and observation that the accuracy of any regular cast bullet that we normally use goes to pot with in a range of RPM. This what we refer to as a "threshold". It's not a hard and fast RPM but an area of RPM where the cast bullet's accuracy goes to pot.

"But when all is said and done, what Larry finds will add to knowledge with lead and RPM's but will not aid in choosing a boolit for a rifle that someone wants to shoot fast.
Maybe I am completely missing Larry's point though! :confused"

Let me clarify the point for you. I am conducting a test to determine if it is RPM that causes the cast bullet to loose accuracy. If it is RPM then in what range of RPM does that generally occur. As to assisting someone who wants to choose a cast bullet design for attaining accuracy beyond the RPM threshold at higher velocity; I will no doubt include my thoughts and suggestions on that very topic in the conclusion portion of the test.


Larry Gibson

[felix]

We really don't care, John, if the darn object flies like a football or not in practice, but for this test I think we want the football to be completely round in flight with zero wobble. How the nose is pointed (attitude in airplane terms) in relation to the tail is immaterial. The nose must go into the wind to maintain course, and that has a lot to do with the RPM and where the center of pressure on the entire football/boolit/plane is. For some reason, the jockies around here love the A-10 flying capabilities versus the F-16, for example. The airbase here had a plane change a couple of years ago (the same pilots for the most part). ... felix

[sundog]

"Another point is that twist rate makes fixed number of RPMs unless velocity is increased. As velocity increases, time of flight goes down. The bullet actually rotates LESS to the larget as you go faster. So higher RPMs actually occur as it slows down."

Bass, whoa. Over a given distance a boolit will turn the same number of times, regardless of velocity. RPM can change, but the number of turns in a given distance is a constant fixed by barrel twist. 1 in 10 remains 1 in 10 regardless of velocity. Or did I miss what you were saying?

[oso]

Well, I can't spell, and I can't do everything right all at once the first time, so I can't contribute to the general fund of human knowledge (but I used to give at the office.) I do appreciate those that try to contribute. My advice is to have fun no matter what they said to Galileo. Just waiting for the wind to diminish so the dust doesn't further obscure the view through my cataracts.

[pdawg_shooter]

Pdowg

So ok that is 2200 fps at what RPM, or with what twist? The paper patch is just like a jacket as it protects and supports the bullet from nasty things happening in the bore during accelleration. Thus it is not nearly as unbalanced and thus the RPM doesn't effect it as much. If your rifle has a 12" twist then the RPM is 132,000 right in the middle of the RPM threshold and it should shoot accurately. If the twist is a 10" then let me ask if the accuracy is not better down around 1800-1900 fps? If the twist is slower than 12" then you've not been paying attention.

As to the 300 RUM; what do you mean by "no problems"? The question pdawg is not how fast we "can" drive a cast bullet. We know we can drive them fast. The question is at what RPM do we begin to loose accuracy. What kind of accuracy did you get at said 3500+ fps with the cast bullet? Was accuracy better down in the 1800-1900 fps range?

Larry Gibson
I shot this bullet from 1562fps to 3528 (10 shot avg.). All shot into 1.25" to 1.85 inches. This is just about what this rifle does with jacketed. BTW the twist is 1 in 10.

[Larry Gibson]

Bass Ackward

"Was that good or what? "

No bass, that was not good. The following is why.

"<<Is a 3,000 psi difference in the pressure curve between the rifles going to skew the test results when there is 5,000 psi +/- ES for the same load in each rifle? Is a velocity difference of 100-500 fps going to skew the test results. No they are not because we are looking for trends not exactness.>>

This is the fundamental difference between us. And apparently the key to my success. "

Bass, if your pressures are exactly the same shot to shot, if your velocities are the same shot to shot and if your bullets hit exactly the same shot to shot then you are the man, a true anomaly, one of a kind and the rarest of the rare. However, you and I and everyone else knows that is not true. There are always variances and these are taken into account. That is scientific standard and it is industry standard. The "key to your success"? You still haven't shown us (we know you can take pictures and post them) any of those .9something groups you shot at 2800 something fps out of your '06. Could you shoot five 5 shot groups consecutively for us? Ok how about five 3 shot groups? Hmmmmmm....ok three 3 shot groups? That's a much simpler test than I am about to do and should be of little trouble to a man of your success.

"I had an epiphany! I always wanted to be able to say that. Won't tell you where this occurred either as this is a family friendly site. :grin:"

Don't hurt yourself, that kind of mental exercise can be dangerous for us old guys!

"Say for a second I am WRONG. RPMs can't be the reason either. And I will put forth the logic.

We know that RPMs of a bullet slow very little over a bullets flight. You have stated this before. Do you agree? Has anyone read of a test where this has been proven fact?"

That is a fact. Every time someone shoots a bullet at long range the test is made and proven. The bullets remain stable all the way down range. The slower a bullet goes the more twist (RPM) is required to stabilize it. (note; the .300 Weatherby's 12" twist. That twist at the velocity of the Weatherby will stabilize a 220 gr bullet. That 220 gr bullet will not be stabilized in the 12" twist of a .308 Winchester at .308 velocities.) ( Thus as the bullet slowed down if the RPM also slowed down the bullet would destabilized and tumble. This does not happen ergo the RPM of the bullet slows down very little over the time of flight. As an example; lets take a tire that is spinning at 1,000 RPM and stop the force that is spinning it. How long does it take to stop spinning? For S&Gs let’s say 10 seconds. Now increase the RPM of that spin to 100,000 and then stop the force spinning it. How long now will it take to quite spinning? A lot longer than 10 seconds I's guess. Now lets take a bullet spinning at 156,000 RPM (a bullet at 2600 fps out of a 12" twist - typical .30 cal match load). What is the time of maximum flight if we shot it as far as it would go? I don't know but lets just say 5 seconds. How much has the RPM slowed down over the time of flight in those 5 seconds, not very much at all. [/B]

"Once a bullet is unbalanced and leaves the bore that way, it will remain unbalanced until it contacts earth."

Can you believe we agree on something again and in the same post!

"If "Over RPMs" were the cause of wobble of an unbalanced bullet, then that bullet would be wobbling all the way to the target. A "permanent condition of flight" because balance will not change after launch. And rotation will not slow. Sound logical?"

You got it.

"All of the holes in any target, at any range, of an unbalanced slug that is over RPM'd would have to be oblong until that slug contacts earth. If "over RPMs" was the cause..

OR .... then the theory about RPMs not slowing down would have to be wrong. Can't have it both ways with Physics."

Bass, your thinking here is where you’re going wrong. Every bullet we shoot is unbalanced when it leaves the bore. There are always differences between the center of gravity and the center of form. That's why we shoot bullets into groups instead of into one hole every time. Because a bullet is wobbling, yawing or even cork screwing in flight does not mean it is not flying point forward. Besides lets say the bullet wobbles .005" in 1 foot of travel. The bearing surface of a 174 gr M118 bullet is .4". Thus the bullet wobbles as it goes through the target paper 1/30th (12" travel in 1 foot divided by the .4" bearing surface) of .005" (the total wobble in 1 foot of travel). That is a whopping .00016". Now if you can see a bullet hole in a paper target is that much "oblong" then you are indeed, the man. Bass, what I'm telling you here is that you and I and everyone else here have seen bullet holes of groups in targets that barely held paper. Those groups were so large that it was obvious the bullets were unstable and flying off into never, never land. Those bullet holes all appeared perfectly round in the target, didn't they. [B]

"BUT ............ if the holes are round, then RPMs turned out to be my correcting friend .... and stabilized flight eventually occurred. The key being how long the unstabilized slug was exposed to air before it stabilized and how fast (velocity) of the headwind was. In other words, the faster you drove it, the crappier groups got. And we do know that velocity is directly proportional to pressure."

[B]You must be shooting into some horrendous headwinds is all I have to say. The wind does in fact effect the flight of a bullet and that is a known fact. I do not believe that even a very strong headwind on a WFN bullet that is stabilized leaving the barrel will become unstable because of the wind over the course of 100 yards. However, keep in mind I'm not going to conduct the test in a horrendous head or tail wind. Additionally, are you now disagreeing with your previous statement of?; "Once a bullet is unbalanced and leaves the bore that way, it will remain unbalanced until it contacts earth."


"Another point is that twist rate makes fixed number of RPMs unless velocity is increased. As velocity increases, time of flight goes down. The bullet actually rotates LESS to the target as you go faster. So higher RPMs actually occur as it slows down. "

Either you're kidding me here or you really don't understand how a bullets RPM are calculated.

RPM is based on rate of twist, and velocity (time). After all it is Revolutions Per Minute with the minute being the time. A bullet fired from a 12" twist will make 1 revolution for every 12" it travels. So it is true that it will only turn 360 times from the muzzle to a 100 yard target. However, how fast the bullet gets there is the "time" and we use the feet per second speed of the bullet to calculate the RPM. So what does this mean to the stability of a bullet? Or why is there any difference between a bullet at 1,000 fps or at 2,600 fps as either bullet if they both make the same number of revolutions to 100 yards? The answer is in the time it takes to get to the target. The 2600 fps bullet gets to the target much quicker and makes that same amount of revolutions in a much shorter time. Thus for the same amount of flight time with each bullet the 26oo fps bullet makes many more revolutions than the 1000 fps bullet, i.e. it has a higher RPM. Now then since we've got that straight you ask, so what? Well the higher RPM generates a much higher centrifugal force. It is that higher centrifugal force of the higher RPM that has a greater effect on the rotational stability of an imbalanced bullet. All of which fits very nicely within the laws of physics. Thus there isn't really "two ways about it." That is the way it is.

"I just saved you all that time and money testing. :grin:"

Would that you did...........

Larry Gibson

[Larry Gibson]

I shot this bullet from 1562fps to 3528 (10 shot avg.). All shot into 1.25" to 1.85 inches. This is just about what this rifle does with jacketed. BTW the twist is 1 in 10.


Interesting, tell us what the groups were in what velocity ranges please? Also was that one 10 shot group covering that velocity range or was that a bunch of 10 shot groups covering that range (which is what I'm assuming)?

Larry Gibson

[BABore]

When your groups decide to open up on you, how are you going to determine that it's caused by excessive rpm's and not;

- Harmonics in the bbl, bedding etc. being off the node.

- Powder charge. We've all worked up loads with a given powder where there is a point where accuracy is best. Any increase or decrease will open groups.

- Pressure, alloy, and bullet fit. With these being off-the-shelf molds any thing less than an exact match to your chamber's neck area, throat, and bore can allow the bullet to obturate unevenly when said alloy's is pushed too hard.

- Bullet lube and lube capacity. Low velocity stuff is less demanding is regards to lube quality and amount. The opposite is true at high velocity. A high end (slick) lube can cause you as many problems at low end as a poor lube at high end.

The reason I'm asking this is because the items I've mentioned are just some of the things that must be addressed if you want to shoot well beyond your theoretical rpm limits. If you lock in some of these factors, and not consider the affects others may or may not have, how to you know that rpm's were exceeded and not one of the other factors.

[pdawg_shooter]

Interesting, tell us what the groups were in what velocity ranges please? Also was that one 10 shot group covering that velocity range or was that a bunch of 10 shot groups covering that range (which is what I'm assuming)?

Larry Gibson

I will have to consult my shooting logs for the particulars but as I recall the best group shot averaged a little over 3460 and was 1.25 for 10 at 100yds. All loads were shot in 10 shot groups for velocity and accuracy. Powder was AA8700 and primers were federal 210s. Brass was Rem, flash holes deburred pockets uniformed and necks turned to .012. The rifle is a Savage116 with a Simmons 3.5x10.

[Larry Gibson]

When your groups decide to open up on you, how are you going to determine that it's caused by excessive rpm's and not;

The reason I'm asking this is because the items I've mentioned are just some of the things that must be addressed if you want to shoot well beyond your theoretical rpm limits. If you lock in some of these factors, and not consider the affects others may or may not have, how to you know that rpm's were exceeded and not one of the other factors.

BABore

Go back and read the first post, i.e. Chapter 1.

The measurements taken with the M43 will tell me when the bullet is being effected in flight by RPM. If we have group opening and the DRV, TOF and BC are the same as with a good group then we know RPM is not causing the group opening especially if we don't have good internal ballistics via the measurement consistant pressures with consistant muzzle velocities. However, if we have good internal ballistics and lessoned DRV, TOF and BC then we know the bullet is being imbalanced during accelleration.

That's how we will know.

Then when we have a bullet with some potential for HV we will focus on one load with consistant internal ballistics and then change other things (burning rate of powder, lube, alloy hardness, sizing of the bullet and even barrel bedding) one at a time and test to see if there is an improvement in accuracy.

Larry Gibson

[HORNET]

So, Larry, When you going to the range? This ought to give some interesting results no matter what else happens. Of course, its probably going to take you about as long to do the data analysis as it does to do the shooting........

[35remington]

pdawg, you do realize that you are claiming the equivalent of cold fusion with your velocity/accuracy claims with lead bullets?

Inch and a quarter ten shotters at 100 yards with a .30 caliber lead bullet at 3400+ fps? Is this your claim? Did I read this correctly?

This would be a first.

[Larry Gibson]

So, Larry, When you going to the range? This ought to give some interesting results no matter what else happens. Of course, its probably going to take you about as long to do the data analysis as it does to do the shooting........

Soon as the weather turns, it snowed here last night! I would like it to be in the low 40s when I head for the range at aound 0800. Hopefully Spring will sprung and it will happen soon.

Larry Gibson

[Larry Gibson]

pdawg

I copied this from the thread on HV .30 cal bullets;

"I like the 311466 Lyman, pure linotype, sized .301 and patched up with 16lb paper. Lube is BAC."

This wouldn't happen to be the cast bullet you're refering to on this thread is it?

Larry Gibson

[shooter93]

Larry.....I think it's a good test and I think you are correct in your assumptions. It's been my experience that a threshold exists as you suggest. I've shot tons of rounds myself which indicate the same. If ....although I'm not sure how...there is anyway I can aide you with this test....supplying powder, primers whatever...let me know. I don't shoot 30 caliber myself...I know...heresy....so I'm wouldn't be much help with bullets unless someone lends me a mold to cast some for you.....or maybe a bottle of Bourbon....just to aide you in persevering?

[Bass Ackward]

"Another point is that twist rate makes fixed number of RPMs unless velocity is increased. As velocity increases, time of flight goes down. The bullet actually rotates LESS to the larget as you go faster. So higher RPMs actually occur as it slows down."

Bass, whoa. Over a given distance a boolit will turn the same number of times, regardless of velocity. RPM can change, but the number of turns in a given distance is a constant fixed by barrel twist. 1 in 10 remains 1 in 10 regardless of velocity. Or did I miss what you were saying?


Yea that's what I wrote yesterday. What an idiot.

I m trying to look at this from all sides to consider everything and the complexity is apparently more than my mind can handle. Hopefully it's the time of day.

[joeb33050]

Larry;
How come your RPM posts get pages of replies and bickering and theorizing, and my extremely interesting and scientific posts on powder position sensitivity get NONE????
I'm jealous!!
joe b.

[45 2.1]

pdawg, you do realize that you are claiming the equivalent of cold fusion with your velocity/accuracy claims with lead bullets?

Inch and a quarter ten shotters at 100 yards with a .30 caliber lead bullet at 3400+ fps? Is this your claim? Did I read this correctly?

This would be a first.


Interesting....... I would note that he is useing a paper jacket on that lead bullet (note the term bullet here). People who use a guilding metal jacket (as in jacketed bullets) do the claim above most of the time also, especially where the cartridge is capable of getting that weight bullet to that velocity. pdawg is useing an alloy suitable to be driven that fast providing it is protected from the powder temperature (which the paper does). His "claim" as you put it does seem quite valid if you look at it from a jacketed view. The main failure, from nasayers, in getting high velocity with unprotected lead alloy is the method and alloy used. High velocity lead loads have been reported for many years in various publications. Even Col. Harrison wrote of 3,000+ fps in useing PP cast boolits in a 300 Win Mag with good accuracy. Anybody want to call him out?

[pdawg_shooter]

pdawg, you do realize that you are claiming the equivalent of cold fusion with your velocity/accuracy claims with lead bullets?

Inch and a quarter ten shotters at 100 yards with a .30 caliber lead bullet at 3400+ fps? Is this your claim? Did I read this correctly?

This would be a first.

Have you ever tried it?

[Bass Ackward]

You must be shooting into some horrendous headwinds is all I have to say.


Larry,

Yea the RPM line was thinking out loud and embarrassing today.

Trying to explain why has me grasping at straws. I'm out of my element. The problem is that I don't have the education to argue my point in this fashion. And if truth be told, I don't have the desire to educate myself to try to explain it either, because I don't think anyone will ever put it totally together.

So I am going to stop theorizing and go with what I have seen.

Internal dynamics are different than externals. I can work to control the internals until I launch it. When I do and I get things correct with a firearm that can do it's part, RPMs does not stand in the way of accuracy.

Now whether or not that is the best accuracy that gun will produce or not, sub MOA at low velocity, is the same as sub MOA at high velocity. Are there more powders and bullet designs that work down low? Yes. Will success become less as you ask for more velocity. Yes. But even down low, one combo works better than everything else. Just when things go well easily, we don't look for a monster.

After thinking on this most of the day yesterday, dad summed it up with one line. Worry about the things you can control. Wind resistance is the same for everyone and so is RPMs. Bullet balance and the exit launch are the only thing we have some input on. Is it our fault the bullet goes outta balance? Along with the mechanicals of the gun .... Yes. That is the problem I have with focusing on RPMs. Launch a bullet design well with a good BC and RPMs is a non factor.

Why it goes screwy is of little importance to me except that I know that meplat shape will minimize what does go wrong. Science be damned, that's what works.

What I want to say is that your test is going to show improvement from lower RPMs and less air deflection. But one bullet design, one powder combination will perform better than the others because it will result in a better launch with less outta balance. So there will be another factor at work there than just RPMs or ballistic coefficient wouldn't matter.

If you REALLY want to fight RPMS, take a 6.5X55 and get a mold made for a 75 grain bullet and a throat cut for it and watch the numbers you can put up. Cause the less bullet weight will allow you better bullets up to a certain point. That point will be much higher than someone forced to launch 140s in the same twist.

Dad said it, don't lose sight of the prize, if you don't launch defective bullets, they go where they are supposed to no matter what twist you run or what RPMs you crank. Worry (take steps) about what you can control. Or don't, and blame something else.

[BABore]

BABore

Go back and read the first post, i.e. Chapter 1.

The measurements taken with the M43 will tell me when the bullet is being effected in flight by RPM. If we have group opening and the DRV, TOF and BC are the same as with a good group then we know RPM is not causing the group opening especially if we don't have good internal ballistics via the measurement consistant pressures with consistant muzzle velocities. However, if we have good internal ballistics and lessoned DRV, TOF and BC then we know the bullet is being imbalanced during accelleration.

That's how we will know.

Then when we have a bullet with some potential for HV we will focus on one load with consistant internal ballistics and then change other things (burning rate of powder, lube, alloy hardness, sizing of the bullet and even barrel bedding) one at a time and test to see if there is an improvement in accuracy.

Larry Gibson

I did go back and reread your first posting. I also noted you stated this;


Now wait a minute you say, by increasing velocity we are increasing acceleration and the bullet is deforming in the bore through obturation and set back. That is the reason for the poor accuracy. Well that sometimes may be the case. However remember, we are using the same loads in each rifle so if the 10” twist rifle becomes inaccurate before the 12 and 14” twist rifles with the same load then we can assume it is the increased RPM of the 10” twist barrel is the culprit. Then if the 12” twist rifle also becomes inaccurate before the 14” twist rifle, all with the same load, then we have confirmed it is the increased RPM that is causing the inaccuracies.

How do you know when it "sometimes" is the case and when it "sometimes" is not. You've got three different rifles that each have a different twist. I realize that you are testing accuracy based on each rifle on to itself. Fine! But since your using the same bullet and load in each rifle, they are now linked. Each rifle has its own chamber neck diameter, throat, and bore. They are not identical are they? Are the bullets used an exact match to these critical alignment features of each gun. No! Since that are not an exact match, are they either too tight or too loose by the same amounts. No!

Your alloy hardness of 14-18 Bhn is a bit on the soft side and will slowly begin to obturate as pressure and velocity are increased. JoeB posted a pressure/Bhn chart awhile back showing where an alloy would start to oburate. Accuracy in each gun will slowly degrade as obturation is increased, but the rate of this degradation will vary based on the bullet fit to each gun. The gun with the poorest fit should demonstrate this first. What if this is the 1 in 10 twist gun. Is that now the "sometimes"? Can your M43 tell the difference between excessive rpm and a canted bullet base while it's still in the barrel. If so, I would like to hear something from Ken on this. They will appear identical on the target. Both cases will cause yaw and be slower to the target.

I would think that to make this test valid, you would need to have each gun have identical internal dimensions except for twist. Then you would need a bullet that would fit them. Your alloy should also be adjusted so the hardness is compatable with the pressure generated. To isolate twist as a study you must eliminate all the other variables.

[Larry Gibson]

Larry;
How come your RPM posts get pages of replies and bickering and theorizing, and my extremely interesting and scientific posts on powder position sensitivity get NONE????
I'm jealous!!
joe b.

I managed to read your post late last night and was going to mull it over and then take a closer look at your results before responding. My initial thoughts are that you've done a good job at demonstrating that powder "position sensitivity" does vary with different powders. Were you going to make any observatioons or conclusions?

Let's switch over to your thread for further discussion as it belongs there, ok?

Larry Gibson

[sundog]

I'm kinda curious about something. If a boolit fits, then where does it obturate to?

When we talk about fitting to a throat, that is generally larger than groove. So, if it does obturate before going through the throat, it's just going to squeeze back down to groove, theoretically providing a seal.

Then, we get into a situation as to whether the alloy can withstand the rotational force of the rifling --- or strip, fully or partially. If it strips, it seems reasonable that gas would by pass, thus reducing pressure. Just thinking out loud...

One other thought, depending on this obturation thing and what it might due to the boolit base. Given a good barrel and good crown, if obturation is not good or even, what happens transitioning from internal to external ballistics, i.e., exiting the barrel?

[Larry Gibson]

Interesting....... I would note that he is useing a paper jacket on that lead bullet (note the term bullet here). People who use a guilding metal jacket (as in jacketed bullets) do the claim above most of the time also, especially where the cartridge is capable of getting that weight bullet to that velocity. pdawg is useing an alloy suitable to be driven that fast providing it is protected from the powder temperature (which the paper does). His "claim" as you put it does seem quite valid if you look at it from a jacketed view. The main failure, from nasayers, in getting high velocity with unprotected lead alloy is the method and alloy used. High velocity lead loads have been reported for many years in various publications. Even Col. Harrison wrote of 3,000+ fps in useing PP cast boolits in a 300 Win Mag with good accuracy. Anybody want to call him out?


45 2.1

That is all well and fine but there is a distinct difference between the PP'd bullet pdawg used and the regular cast bullets we are discussing. That is, as you mention, the PP jacket protects the bullet. This is definately apples to oranges with the use of PP bullets being not germain to this discussion and topic. If anyone wants to object that it is "germain" then where do we draw a line? After all if one casts the core to be used in a swaged jacketed bullet is that then not a "cast" bullet? What about Speer's "HotCor" bullets, would they not technically be "cast" bullets?. No they are not and neither is the PP cast bullet for the purposes of this discusion. Point being; this test concerns if there is a RPM threshold and if so, how and when does it effect regular cast bullets.

Larry Gibson

[45 2.1]

45 2.1

That is all well and fine but there is a distinct difference between the PP'd bullet pdawg used and the regular cast bullets we are discussing. That is, as you mention, the PP jacket protects the bullet. This is definately apples to oranges with the use of PP bullets being not germain to this discussion and topic. If anyone wants to object that it is "germain" then where do we draw a line? After all if one casts the core to be used in a swaged jacketed bullet is that then not a "cast" bullet? What about Speer's "HotCor" bullets, would they not technically be "cast" bullets?. No they are not and neither is the PP cast bullet for the purposes of this discusion. Point being; this test concerns if there is a RPM threshold and if so, how and when does it effect regular cast bullets.

Larry Gibson

I really don't see this as your concern since it was directed at 35remington. The ejecta from a PP boolit is still a naked boolit exhibiting the same characteristics for the alloy used as a cast one would be, dependent on the hardness and ductility of the alloy and if it was cast in the first place out of a conventional grease groove mold. You have stated this is external ballistics several times now. It's apples and oranges only when dealing with swaged cores.

Should you want to discuss something, maybe you could elucidate on the built in alloy failure that will be caused from your stated parameters of trying to use a 14 to 18 BHN alloy at 2600 fps maximum (your alloy will fail at a much lower level). Several formulas will give a much higher BHN to accomplish that. You have too many variables and failure mechanisms to reach any definite conclusion to your experiment. Any conclusion would be an assumption on which caused what.

[felix]

Corky, stripping occurs at the ogive end of the boolit first, and hopefully the stripping action does not go much further than, say 3/4 of the way, through the entire bearing length. We can measure the land impressions of the fired boolits and see how long the tails are, and how wide. If the width is the same as the unfired boolit, we can assume with confidence the rotation is as calculated. The tail lengths should all be zero indicating the use of the most perfect alloy and lube for the application which never will happen. Closer to zero length, the better. Closer to the same width of the lands, the better. The width deviation MUST be zero across the gas check as a minimum. ... felix

[pdawg_shooter]

I really don't see this as your concern since it was directed at 35remington. The ejecta from a PP boolit is still a naked boolit exhibiting the same characteristics for the alloy used as a cast one would be, dependent on the hardness and ductility of the alloy and if it was cast in the first place out of a conventional grease groove mold. You have stated this is external ballistics several times now. It's apples and oranges only when dealing with swaged cores.

Should you want to discuss something, maybe you could elucidate on the built in alloy failure that will be caused from your stated parameters of trying to use a 14 to 18 BHN alloy at 2600 fps maximum (your alloy will fail at a much lower level). Several formulas will give a much higher BHN to accomplish that. You have too many variables and failure mechanisms to reach any definite conclusion to your experiment. Any conclusion would be an assumption on which caused what.

Well said ! If rpm effects a lubed bullet it will also effect a paper patched one. Reminds me of a post about a as cast bullet being .003 out of round and if this should worry a caster. It might go into the barrel out of round by I think the only way it could leave the barrel out of round is if the bore is not round!

[pdawg_shooter]

BTW, an alloy of BNH14.0 to 14.5 works well at 2600fps..IF.. it is paperpatched. The Lyman 311284, cast of this alloy is a great hunting bullet in my 30-06 at this velocity.

[Larry Gibson]

Bass

Your education has nothing to do with your intelligence. This only takes the ability to grasp a concept. I believe you have the intelligence and ability.

"
Internal dynamics are different than externals. I can work to control the internals until I launch it. When I do and I get things correct with a firearm that can do it's part, RPMs does not stand in the way of accuracy.

Now whether or not that is the best accuracy that gun will produce or not, sub MOA at low velocity, is the same as sub MOA at high velocity. Are there more powders and bullet designs that work down low? Yes. Will success become less as you ask for more velocity. Yes. But even down low, one combo works better than everything else. Just when things go well easily, we don't look for a monster."

This is the block you but up and is exactly why you're not grasping the concept. I've not said accuracy at high velocity with a cast bullet can not be had, now have I? What I and others are saying is that there is a RPM threshold that prevents regular cast bullets from being shot with as good or better accuracy above that RPM threshold as those same bullets shoot in or below the RPM threshold. Can ou shoot a 311291 as accurately out of your 10" twist '06 as it shoots at 1800-1900 fps inside the RPM threshold? Can you shoot any regular cast bullet more accurately out of that '06 at 25-2600 fps than that same bullet shoots in or below the RPM threshold? No you can't Bass, you know that and we know that.

However you state you can shoot a specially designed bullet, with special loading technique, using certain componants, only on certain days with the temperature just right, and the bullet sizing just right very accurately, but only if you've properly adjusted the barrel bedding pressure.

That is not Joe average poster here who just gets a common Lyman, RCBS, Lee or Saeco mould and casts some bullets from WWs and loads them up using regular cast bullet loading techniques for his 10" twist '06 who wonders why he can't get accuracy at higher than 1800-1900 fps. Joe average poster is loading his cast bullets a far cry from the way you do, isn't that correct?

Now, to tell Joe average poster to stand a certain way, wait for the moon and stars to line up with jupiter, rebarrel/recahmber his rifle, rebed his rifle, buy a custom mould, buy five different lubes, buy 5 differnt bullet sizers or divorce his wife IS NOT going to answer his question. That question being; "Why can't he get his 311291 to shoot as accurately at 22-2500 fps as it does at 1800-1900 fps". The answer to his question is the RPM threshold.

"After thinking on this most of the day yesterday, dad summed it up with one line. Worry about the things you can control. Wind resistance is the same for everyone and so is RPMs. Bullet balance and the exit launch are the only thing we have some input on. Is it our fault the bullet goes outta balance? Along with the mechanicals of the gun .... Yes. That is the problem I have with focusing on RPMs. Launch a bullet design well with a good BC and RPMs is a non factor."

Your father is correct, you should listen to him;-) The broblem is you think we should "focus" on RPM. That is not the case. We should understan RPM and the threshold. When we understand it then we can work on those things to negate its effect and can we can cross the trheshold. You do understand that Bass, you just don't realize it. You know we are not going to launch a regular cast bullet accurately at 22-2500 fps from a 10" twist barrel. That is why you state, correctly BTW: "Launch a bullet design well with a good BC and RPMs is a non factor".

Thus it is obvious you understand the concept of the RPM threshold. You are just not grasping it is all. I think you ARE smart enough to grasp that Bass

"What I want to say is that your test is going to show improvement from lower RPMs and less air deflection. But one bullet design, one powder combination will perform better than the others because it will result in a better launch with less outta balance. So there will be another factor at work there than just RPMs or ballistic coefficient wouldn't matter."

"perform better than the others because it will result in a better launch with less outta balance". This is why it will have a better BC and the RPMs centrifugal force will effect this type of bullet less. But, as you know, 311291 is still going to be adversly effected at velocity above the RPM threshold. That is not only "the way it is" but it is also "science".

"If you REALLY want to fight RPMS, take a 6.5X55 and get a mold made for a 75 grain bullet and a throat cut for it and watch the numbers you can put up. Cause the less bullet weight will allow you better bullets up to a certain point. That point will be much higher than someone forced to launch 140s in the same twist."

I don't need to fight RPMs in a 6.5 Swede as I've already done it and will do it again. However, telling someone who wants to shoot 140 gr cast bullets accurately above 1700 fps in his M96 Swede to buy a new mould and a new barrel isn't answering the question, is it? Telling him he won't get there from here in his M96 with the 140 gr bullet because of RPM will answer the question. Then if he wants to pursue HV in A 6.5 Swede your answers are valid.

BTW; given my own Swedes with military barrel/chambers I've found the Lyman 266455 to be about the best regular cast bullet to push the RPM threshold with. It fits the throat and neck of my Swedes perfectly, has a long bearing surface to short nose ratio and casts out at .267-.268".

Larry Gibson

[405]

Larry,
No problem I can see with the test within the constraints of money and time. Seems pretty valid- set the hypothesis, minimize the variables and go for it. I also like the idea, brought up earlier, about a possible "series 2" test using two or three different powders keeping other parameters same. Fast powder, medium powder and slow powder- may shed some light on the acceleration thing.
No need pulling hair out over all the "ya buts" and "what ifs" before the tests are even run :confused:

[felix]

Larry, thinking more about Corky's inquisition on this matter, and combining his with Babore's, perhaps a good method for comparison between the guns would be by measuring the the demarcation for each gun where stripping just begins. Increase the load, always using the best and same boolit for all the guns, and changing only powder speed and amount, until stripping becomes optically the same. That SHOULD eliminate all the variables except for the twist. The velocity obtained from each SHOULD be progressive from the 10 incher to the 14. Gun's baselines' would be your condom boolits' opticals. ... felix

[Larry Gibson]

BABore

"How do you know when it "sometimes" is the case and when it "sometimes" is not. You've got three different rifles that each have a different twist. I realize that you are testing accuracy based on each rifle on to itself. Fine! But since your using the same bullet and load in each rifle, they are now linked. Each rifle has its own chamber neck diameter, throat, and bore. They are not identical are they? Are the bullets used an exact match to these critical alignment features of each gun. No! Since that are not an exact match, are they either too tight or too loose by the same amounts. No!"

If we were comparing the accuracy of the 3 rifles to each other you would be correct. Since we concerned with how RPM effects the accuracy in each rifle to itself the fact that one rifle may shoot more accurately than another is not relavent. We will compare only the amount of accuracy lost by percentage between the rifles with different twists.

"Your alloy hardness of 14-18 Bhn is a bit on the soft side and will slowly begin to obturate as pressure and velocity are increased. JoeB posted a pressure/Bhn chart awhile back showing where an alloy would start to oburate. Accuracy in each gun will slowly degrade as obturation is increased, but the rate of this degradation will vary based on the bullet fit to each gun. The gun with the poorest fit should demonstrate this first. What if this is the 1 in 10 twist gun. Is that now the "sometimes"?"

All three of these barrels have match cut chambers. I have and will load the test bullets to fit the barrel. The cases are "prepped" with the necks inside neck reamed to very close concintricity. A Match NS die is use to NS the fire formed cases. Bullets are seated to just touch the leade. If you really read Chapter 1 you would know that we are going to also try different sizing of the bullets. How much more "fit" is necessary for 'regular cast bullet loads"? The M43 will tell us the time pressure curve and muzzle velocity. By comparing those loads of the three rifles with the same time pressure curve (within acceptable variation - there will always be variation) and muzzle velocities we will see any anomoly as mentioned. We know the BHN is soft and that is intentional. The obturation , setback and bending is expected to occur at pretty much the same pressure in each rifle. When that occurs we expect to see is an increase in DRV, TOF, and a decrease in BC with the 10" twist first because the higher RPM of that twist will adversely effect the rotaional stability of that twists bullet first. As mentioned in a previous post; if all three are adversly effected at the same velocity (they will have different RPMs) then it will be the pressure that is causing the inaccuracy.

"Can your M43 tell the difference between excessive rpm and a canted bullet base while it's still in the barrel. If so, I would like to hear something from Ken on this. They will appear identical on the target. Both cases will cause yaw and be slower to the target."

The M43 may tell us something is different inside the barrel by differences in the time pressure curve. Also since the bullet is supported by the barrel and the centrifigal force of RPM is totally negated while the bullet is still in the barrel there is no such thing as "excessive RPM" in internal ballistics. "Excessive RPM" only applies to external ballistics (the bullets flight). Yes both cases you mentioned will "cause yaw and be slower to the target". These are measured by the M43 quite precisely; i.e. DRV, TOF and BC.

"I would think that to make this test valid, you would need to have each gun have identical internal dimensions except for twist. ....... To isolate twist as a study you must eliminate all the other variables."

While having three identical rifles except for twist would be nice but it's not necessary or practical. Are you aware that it is common knowledge and been proven many times that two identical barrels, with the same twist even, produced back to back will be different in their shootability? The other variable are eliminated or taken into account.

Larry Gibson

[Larry Gibson]

45 2.1

I did start this thread you know. Thus I think is concerns me especially since it deals with pdawgs remarks. Those were directed at my BTW.

"Should you want to discuss something, maybe you could elucidate on the built in alloy failure that will be caused from your stated parameters of trying to use a 14 to 18 BHN alloy at 2600 fps maximum (your alloy will fail at a much lower level). Several formulas will give a much higher BHN to accomplish that. You have too many variables and failure mechanisms to reach any definite conclusion to your experiment. Any conclusion would be an assumption on which caused what."

Read the response to BABore, it is addressed there....again.

Me thinks thou art protesting too much....again.

Larry Gibson

[sundog]

Felix, suppose you are right that the boolit strips earlier on on the nose. If that does not occur evenly, i.e., the boolit is leaning harder one way, then the boolit nose could begin to wander off center -- the base may not because it is supposedly FULLY supported. Now when the boolit exists the problem is compounded by the boolit base may no longer be square to barrel axis if any wobbling has begun and escaping pressure will exagerate the off centeredness.

This might also happen if groove depths were not constant, either in the same groove, or groove to groove. We've always said that the barrel is a swaging device, but I'm not sure we've ever addressed what the boolit was being swaged to. Even if you would otherwise get a good exit from the barrel, a lousy crown will ruin accuracy.

[felix]

Absolutely no doubt, Corky! ... felix

[Larry Gibson]

BTW, an alloy of BNH14.0 to 14.5 works well at 2600fps..IF.. it is paperpatched. The Lyman 311284, cast of this alloy is a great hunting bullet in my 30-06 at this velocity.

Ok, pdawg

Let's play the same game since you stuck that big "IF" in there. Take that PP off that 311284, size, lube and put a GC on it just like what we're talking about. Then shoot it at 1800 fps, 2200 fps, 2400 fps and 2600 fps. Come back then and talk to us about it.

Larry Gibson

[BABore]

The M43 may tell us something is different inside the barrel by differences in the time pressure curve. Also since the bullet is supported by the barrel and the centrifigal force of RPM is totally negated while the bullet is still in the barrel there is no such thing as "excessive RPM" in internal ballistics. "Excessive RPM" only applies to external ballistics (the bullets flight). Yes both cases you mentioned will "cause yaw and be slower to the target". These are measured by the M43 quite precisely; i.e. DRV, TOF and BC.

This falls right back into the paper patch arguement. How can the soft PP bullet withstand the high rpms after it has left the bbl and stripped itself of the paper. Alot of PP shooters use sized down grooved bullets too. The paper protects the bullet on the internals, but not the external. With this line of arguement it leads me to believe that if something is affecting the bullet's flight, it's happening during launch. Since tweaking bullet fit, alloy, hardness, lube, and load have always allowed me to shoot accurately at HV, this leads me to believe that they are also the problem if not addressed.

[pdawg_shooter]

Ok, pdawg

Let's play the same game since you stuck that big "IF" in there. Take that PP off that 311284, size, lube and put a GC on it just like what we're talking about. Then shoot it at 1800 fps, 2200 fps, 2400 fps and 2600 fps. Come back then and talk to us about it.

Larry Gibson

Why on earth would I want to handicap myself? If it works with paper why would anyone take the paper off?

[Larry Gibson]

felix and Sundog

I've rcovered a lot of cast bullets fired from rifles (30-06 and 300 Weatherby). Many were fired at HV (up to 3000 fps in the Weatherby) in an attempt to find out if bullets "stripped" in the rifling. This test was run with WW alloy (old type of WWs) up through WQ'd Linotype. The only ones with any indication of "stripping" were those fired in long throated chambers where the bullet was some distance from the leade. Then, at most, there was only 1/16" or less "stripping" on the front of the driving band of the 311291. BTW the 311291 bullets were cast using the same mould I'm using for this test. A 311359 bullet was also used. We original hypothesized that the 311291 bullet would show greater evidence of "stripping" before the 311359 because of the greater inertia of the heavier bullet resisting the rifling more. Was not the case however, in the 2800+ fps range out of both the '06 and the 300 Weatherby the 311359 showed "stripping" to ablut 1/8" back from the front driving band. We never did get more than 1/16" "stripping" on the 311291, even with the soft WW alloy and HV.

Larry Gibson

[Larry Gibson]

BABore

"This falls right back into the paper patch arguement. How can the soft PP bullet withstand the high rpms after it has left the bbl and stripped itself of the paper. Alot of PP shooters use sized down grooved bullets too. The paper protects the bullet on the internals, but not the external."

You answer your own question again. It is because "The paper protects the bullet on the internals" that there is far less imbalances to the bullet. Thus the effects of the RPMs centrifugal force are much less on the bullet during flight. Hence, better accuracy. Not to hard a concept to grasp.

"With this line of arguement it leads me to believe that if something is affecting the bullet's flight, it's happening during launch. Since tweaking bullet fit, alloy, hardness, lube, and load have always allowed me to shoot accurately at HV, this leads me to believe that they are also the problem if not addressed."

When you "tweak" the things you are then you are pushing the upper limit of the threshold. Now I will still bet that will all that tweaking your bullets WILL shoot more accurately in or below the RPM threshold than they do at HV, assuming that they are above the RPM threshold. FYI; we can still shoot at "HV" and be under or within the RPM threshold: i.e.; a bullet fired from a 14" twist is still within the RPM threshold at 2700 fps, with a 12" twist at 2325 fps and with the 10" twist at 1950 fps. However, also remember I always have said the RPM threshold can be shifted either way a bit depending on how we tweak the load or by the alloy of the bullet along with the things you mention and several more.

Larry Gibson

[Larry Gibson]

Why on earth would I want to handicap myself? If it works with paper why would anyone take the paper off?

Then why are you even in this discussion as your point is not relevent to this discussion.

Larry Gibson

[leftiye]

The paper patched boolit at 3600 fps (highest I can recall seeing) without accuracy going south throws in a variable that should have put this all to rest, as it muy clearly violates the RPM barrier (My words) which has been placed in the lower to mid 2000s of fps. I don't think it is valid to just shrug this off.

We all could profit greatly at this point if we were to discover HOW CUM? this could happen! Especially if you look at the comparative value of argueing about whether there is an rpm threshold versus the value of knowing how to completely negate any such possibility for another 1000 fps. I agree with the concept that a cast boolit whether or not paper patched is still the same animule, and the same factors apply to launching it.

The paper patch obviously stops something very bad from happening to the boolit. One cannot however go on to claim that a jacket whether paper or copper is a jacket, as the copper variety do not have cast cores (at least not ones that haven't been subsequently swaged). Knowing how the paper accomplishes this would be a valuable insight. It obviously stops all manner of deformation while launching.

[carpetman]

Larry Gibson---Why are you in this discussion as your point is not "relevent " to the discussion. I checked with the department of redundancy department and using discussion twice in this situation would be redundant in this situation. It is relevant ---there is an A---but you continue to use an A in consistent and there is no A.

[pdawg_shooter]

Then why are you even in this discussion as your point is not relevent to this discussion.

Larry Gibson

If rpm destroys, or lessens accuracy, why does it not affect a paperpatch bullet? After all the patch leaves the bullet at the muzzle. Richard Lee states it is pressure that causes the problem and a BHN of 22.0 cannot stand the pressure required to get this kind of velocity. But the paper patched bullet does fine.

[felix]

It is how the RPM is generated, not the RPM itself. That is why it is important to consider only the naked boolit, perhaps with a gas check as the only augmenter. I personally think it has to do with the amount and kind of rifling bite on the projectile which determines the maximum RPM threshold. I do not think Larry should dismiss that parameter as being a constant in his experiments. ... felix

[Larry Gibson]

leftiye

Read my last post to BABore. Your statement of "Knowing how the paper accomplishes this would be a valuable insight" answers your own question. How a PP protects a cast bullet is not the question I am answering with my test. My test is to answer the question how RPM effects a regular cast bullet. It is not how RPM effects ALL BULLETS. In the context of a cast bullet having a jacket around it then are we to consider the swaged jacketed bullet if the core is cast? Are we to consider Speer's HotCor bullets because the core is cast into the bullet? You may want to consider those but I am testing how RPM effects a cast bullet we cast out of a mould, lube and size, attach a GC to it, load it into a rifle cartridge and attempt to shoot it above the RPM threshold. Are we having trouble reading and understanding that?.

Perhaps you would run the test to answer your own question regards the other types of bullets?

Larry Gibson

[Larry Gibson]

Larry Gibson---Why are you in this discussion as your point is not "relevent " to the discussion. I checked with the department of redundancy department and using discussion twice in this situation would be redundant in this situation. It is relevant ---there is an A---but you continue to use an A in consistent and there is no A.

Thank you, I stand corrected.

Larry Gibson

[Larry Gibson]

If rpm destroys, or lessens accuracy, why does it not affect a paperpatch bullet? After all the patch leaves the bullet at the muzzle. Richard Lee states it is pressure that causes the problem and a BHN of 22.0 cannot stand the pressure required to get this kind of velocity. But the paper patched bullet does fine.

pdawg

Do we not read any other posts other than your own? I have already explained this at least twice in this thread. But for you I will do it again.

RPM adversely effects ALL bullets in flight. To what degree that adverse effect is depends on the imbalances of the bullet. This is why bullets shoot into groups instead of into one hole even with very, very consistant internal ballistics.

You PP'd bullet shoots into groups because it is effected by RPM.

Well I guess you've made fools out of Richard Lee and me haven't you. But then Mr. Lee was talking about the same kind of cast bullet I'm talking about. Mr. Lee and I are not talking about the same kind of cast bullet you are talking about. Hmmmmmm......maybe there's a reason for the difference there, don't you think?

Richard Lee and a whole lot of other people say it is pressure that causes the inaccuracy of regular cast bullets above a certain level. Richard and them are all right to a certain point. Pressure, in fact, causes the regular cast bullet to deform during accelleration. It is the RPM rate that determines at what velocity that deformation will cause inaccuracy. That is what I am conducting this test to find out.

Perhaps you would like to assist leftiye in a scientific type experiment with PP'd bullets testing how fast they can be driven with accuracy? All of us would love to hear about it. But it is not relevant (that better Carpetman?) to this test.

Larry Gibson

[Larry Gibson]

It is how the RPM is generated, not the RPM itself. That is why it is important to consider only the naked boolit, perhaps with a gas check as the only augmenter. I personally think it has to do with the amount and kind of rifling bite on the projectile which determines the maximum RPM threshold. I do not think Larry should dismiss that parameter as being a constant in his experiments. ... felix

felix

I am not dismissing that parameter in this test. I believe the measurements the M43 will give of the internal ballistics will tell us if that is a viable parameter to consider. The study mentioned previously on rifling engraving by bullets showed there was very little pressure required by a lead bullet to become engraved. Thus if the M43 shows us that the time pressure curve is consistent with the same load in all three rifles then the effects of different rifling is negligible. However if the time pressure curve of the same loads are not consistent in all three rifles then we will need to consider that parameter.

All three rifles have similar type of rifling. The difference between them is 2 rifles of 4 grooves and one of 6 grooves. However all have the same ratio of rifle to groove area so resistance to the bullet engravement should be consistent.

The test will tell us.

Larry Gibson

[felix]

OK, Larry! The bite has to be identical for each of the guns to make the muzzle speed valid for that gun. Here's hoping that the friction at the leade-in is exactly the same, and should be for the same percentage of land interference. The only problem area, then, would be the amount of gas generated, and the length of the barrel. Accuracy should not be considered because even if they did shoot well with the "same" energy, it would be a fluke because of the other factors. ... felix

[Larry Gibson]

OK, Larry! The bite has to be identical for each of the guns to make the muzzle speed valid for that gun. Here's hoping that the friction at the leade-in is exactly the same, and should be for the same percentage of land interference. The only problem area, then, would be the amount of gas generated, and the length of the barrel. Accuracy should not be considered because even if they did shoot well with the "same" energy, it would be a fluke because of the other factors. ... felix

You're right felix

I am not going to consider the "accuracy" as such. I'm going to measure the effect of RPM on accuracy. As I've said earlier if, as the loads are tested, the best accuracy attained is 2 moa or so and accuracy is different for each barrel that is ok. It is when the accuracy of each rifle starts getting worse that we are looking for. When the accuracy starts getting worse and the TOF and DRV get larger and the BC gets smaller proportionally for all three rifles then it is telling us the bullet has sustained some imbalance from acceleration. At the same time if the group with the highest RPM is proportionately larger than the slower RPM barrels then it is telling us that the RPM is adversely affecting the rotational stability of the bullet and some degree of inaccuracy is the result.

Larry Gibson

[garandsrus]

Larry,

If I were you, I think I would stop debating people, run the test as you see fit, and then publish a magazine article with the test and results in the Fouling Shot, Precision Shooting, or elsewhere...

You are going to spend a lot of time and resources with what you are proposing.

Thanks for doing this. I am looking forward to the outcome!

John

[Larry Gibson]

Larry,

If I were you, I think I would stop debating people, run the test as you see fit, and then publish a magazine article with the test and results in the Fouling Shot, Precision Shooting, or elsewhere...

You are going to spend a lot of time and resources with what you are proposing.

Thanks for doing this. I am looking forward to the outcome!

John

I do believe that is what I will do. Thanks

Larry Gibson

[runfiverun]

larry i think you may see on the 43 a spike or dip on the pressure rise
if the boolit is tipping or obTurating?

and who says we dont cast jacketed boolits?
have some very and not so very nice groups with my cast bullets
maybe i will spell it bullIts.

i would be verrrrry interested in a patched/cast test and posting!!

[35remington]

pdawg, in .22 caliber, yes.

I'm afraid I'm going to be from Missouri on this one, paper patched bullet or not.

I realize no one is obligated, or intends, to supply any proof of anything here. Quite frankly, these responses get progressively more stupid as each poster dissects the endless minutiae of another's post and the whole thing is less about explanation and advancing the craft and more about who can argue the most bullheadedly.

I tire of guys who just talk and piss the loudest. If anything on any gun forum deserves a resolution, this topic does.

Ante up, boys.

Make the posts relevant. I wonder why no one is showing up at matches with these tried and proven high velocity techniques? Think of the positive press you would get. You would be, quite literally, God Of Cast Boolits. Or is this discussion about results that are not reproducible on demand?

Spare me "the information is proprietary and I'm not gonna enlighten you if you don't know" rhetoric.

[joeb33050]

I'd like to know if there's an RPM threshold beyond which accuracy deteriorates. Testing will show if there is or is not, with the test set of conditions. I'd like to add the topic and test results to the book.

That said, I was reading the additions to the thread, the opinions and theories and dog/hydrant remains, when I had a thought. Yes, it happens on occasion.

I shoot cast bullets in rifles mainly, at velocities WAY under 2000 fps. I shoot cast bullets because there's little recoil, less noise than HV or jacketed, and because it is about impossible to wear out a barrel- as long as low velocities are maintained.
Because of the recoil, noise and wear, I don't shoot at high velocities, so from that standpoint the RPM threshold is of only academic interest-I want to know, but the results won't change the way I load and shoot.

I don't hunt but if I did hunt I'd buy factory ammo or load jacketed.

Accuracy-making small groups and/or large scores at known ranges accuracy-is about as good at low velocities as at high velocities in the CBA matches. The LV breech seating single shot guys do as well as or better than the higher velocity bolt gun guys.

So, if we can have low recoil and noise and wear and good accuracy at low velocity, why-except for hunting-do CB shooters care about high velocities? Or that RPM accuracy threshold?
joe b.

[sundog]

I posted some results for 844(PD) on castpics a few years ago for 30-30 and 32 Win Spl. Here's how i did it (and do this quite often to test new combinations). Kept all other things equal and increased charge until accuracy went south or get into too much pressure to be safe. As charges increased I actually got smaller groups until they finally did start to open back up. So, for a given set of conditions, best accuracy was found - just back off to the smallest group and see if it is repeatable. Change something, anything, and you have to start over. That 'anything' could be boolit design, alloy or hardness, loob, powder (even lot #), the wx, etc. I've always said that it's the equipment and components that will tell you the best load. You don't just pick a load out and say, "yup, that's what I'm gonna use. I'm gonna shoot boolit X at velocity Y." You gotta go discover it.

So, if I understand you correctly Larry, you are basically going to do this same thing, but you will have a strain guage on the platform(s). Right? If that's the case, it will be interesting to actually 'see' what's going on, especially if you get into the mid to high 2Ks with repeatable results.

[carpetman]

Larry Gibson---You are most welcome and making some progress. Now go to your post #110 and you are still using an A in consistent---half way there.

[Larry Gibson]

joe b.

"So, if we can have low recoil and noise and wear and good accuracy at low velocity, why-except for hunting-do CB shooters care about high velocities? Or that RPM accuracy threshold?"

Hunting and long range shooting are the two main reasons. I'm not into cast bullet bench rest but I'd say they have an interest in that the faster the bullet gets to the target the less time the wind can dance with it. Practicing with a load that equals th recoil and practical accuracy for hunting is possible another. Just my quick thoughts on it. Probably more reasons than that though.

Larry Gibson

[Larry Gibson]

Larry Gibson---You are most welcome and making some progress. Now go to your post #110 and you are still using an A in consistent---half way there.

It is a difficult job getting this computor to spell correctly:-)

Larry Gibson

[Larry Gibson]

Sundog

Yes, that is basically what I am doing. I already know what an accuracy load is for 311291 with H4895. I am starting below that and “working up”. With the volume of shooting to be done in this test I am working up the load in 2 grain increments with 311291. I will start below what I already know is a most often accurate load for the .308. I will proceed well beyond that accuracy load into the HV range for a .308 Winchester using a 177 gr bullet. I will test this series of “working up” loads in each twist. Since using a case full of slow burning powder is often recommended as a way of achieving accuracy at HV I will also test a small range of loads with H4831 and RL19. These will be 90-100% loading density loads.

With 311466, since it is a lighter bullet I will use 1 grain increments when working up the 4895 test loads. I also will use the slower burning powders with 90-100% load density. This test and the above test using the different twist rifles should tell us whether or not there is a RPM threshold where RPM adversely begins to affect accuracy.

When the above tests are complete using the 10” twist rifle and 311466 I will use a HV load with a RPM well above the RPM threshold that has excellent internal ballistics in a +/- 1 grain of powder range. Then we will teak the load changing one thing at a time as you mention. I plan on changing to harder alloys, changing lubes, trying different bullet sizing, changing the powder charge, trying different pressures on barrel bedding, etc. If one thing maintains internal ballistics, increases accuracy, decreases TOF and increases DRV and the BC then it will be incorporated and the next thing will be tested. This will give us an idea of what works with that bullet and may provide a basis for determining if some things don’t work. I will also determine if I can get as good or better accuracy at HV well above the RPM threshold as I get in or below the RPM threshold.

Larry Gibson

[sundog]

Larry, press on! I, for one, am interested. It is a lot of resources that you will use!

[badgeredd]

Me Too Larry.

Interesting to see some of the responses too. BTW I often miss my own goofs! Go figure!

[Ricochet]

Ambitious project! And a very interesting one!

[andym79]

Larry did you complete the test?

[44man]

I might be the least scientific guy here but I see things. I also see so many here that have seen the same things. Since most of my work has been with revolvers using both jacketed and cast, I see why the differences in accuracy. I see what powder speed, primers and lubes do. I also see what twist rates do.
I have the hardest time explaining boolit deformation before the boolit enters rifling and why a straight start is so important without using the cylinder as a size die. How a boolit must "pull" the cylinder and maintain it's integrity to the target. Why a Keith is so hard to shoot good because it can start out of balance if the gun is not perfect. What a GC does and see felix agrees about skid.
Why a short barrel is harder to shoot with accuracy with a certain twist unless you equal the same velocity and spin of the longer barrel without destroying the boolit with fast powders.
Why extending peak is better and why slow twist revolvers are harder to get to shoot. Why the "jump to rifling" is not important with the proper alloy as my BFR 45-70 with about 3/4" jump to a 1 in 14" twist is the most accurate EVER.
Now working with the 30-30 and cast and the brass problems I found set me back some. Run out that Larry also has to address. Run out with cast is common and can skew results BIG TIME. Out of balance boolits before they leave the chamber. I found turning necks and fire forming has brought me to under 1" at 100 with a lever gun. Fit counts of course.
Why do I shoot the groups I do with a .430" boolit from a .4324" throat? Because the boolit will align to the bore, How do I shoot PB at max pressures? I even reached over 55,000 psi with PB with small groups.
Why does a model 29 shoot a 240 gr with rotation around the flight path without losing accuracy?
They key is to reduce variables and Larry must use BR brass preparation to eliminate out of line boolits.
I am a firm believer in the proper twist and the velocity needed for stability so we are on the same page. It is why I can shoot a revolver WFN to 500 meters better then I can with a rifle using any other boolit.
Over spin is better then under spin in almost every case.
The saying to use the least rate for stability only works with with a few things, mostly close ranges. 100 yard cast shooters use slower rates to prevent corkscrewing but at long range spin is not enough.
Any boolit must have a straight start without deforming and the drive area must be right for the velocity and spin. To take one boolit through all the twist rates means each rate needs a different velocity. Bottom line is a boolit will not shoot the same from 1 in 10", 1 in 12" or 1 in 14" unless velocity is changed. Those parameters can't be changed. If a given boolit needs so many thousands of RPM's to resist outside influence and remain stable to the target, you can't alter it.
The only thing anyone can prove is a given boolit needs spun at so many RPM's no matter the twist rate. Time of flight and distance be damned. Over spin and you can shoot farther.
Forget transition to subsonic too. Maintain spin first.
I will stand by it, under spin and suffer what you get.

[Pilgrim]

I believe lack of spin results in lack of accuracy. However too much spin will also result in loss of accuracy. During my Hunter BR shooting days my spin thoughts were seriously bent. This is with jacketed bullets of course. I started out with a 15 twist and 125 gr. bullets in a .30 case (wildcat) slightly smaller than the parent .308 and worried about stability. As the years went by, the winning shooters changed to a 16" twist and then to a 17" twist. Lower spin increased accuracy. Clearly there is a spin that is best. Below spin rate accuracy goes to hell, and accuracy above that spin decreases, but stays good, although not good enough to win. Bullet weights depended upon shooter and his/her mood at the time but generally were in the 125 to 135 gr. range with .30 cal cartridges of one flavor or another, but all were slightly smaller than the .308 Win.. Remember the standard .30 cal. twist is 10" !! The targets were at 100, 200, and 300 yards so "close range" is a relative thing. FWIW Pilgrim

[Larry Gibson]

44man

"Larry" did and does use BR brass preparation.

Also I agree with your conclusion regarding cast bullets in revolvers. However this whole discussion has nothing to do with the lower velocities and RPMs produced by revolvers. While Pilgrim is absolute correct with " Lower spin increased accuracy. Clearly there is a spin that is best" such is related to bullet stability and accuracy. Your comments and observations are also related to bullet spin and stability and how accuracy is affected by such. Both of you are correct.

However, the problem is, as I've stated numerous times, bullet stability/instability and it's related accuracy has nothing to do with the RPM Threshold. The RPM threshold is about bullet imbalance and the adverse affect centrifugal force acting on those imbalances has on accuracy.

As an example; a 30-06 match rifle with a load at 2640 fps with M72 174 gr match bullet and the exact same load using a Sierra 175 gr MK. The M72 bullet shoots into 2 moa and the MK shoots into 1 moa. Both are basically the same design, shape and weight of bullet. The load is the same. The concentricity of the rounds in the chamber are the same. The spin rate is the same (2640 fps out of 10" twist barrel). The rotational stability of the bullet in flight is the same. So then why the difference in accuracy? The answer is simply because the MK is a much better balanced bullets in jacket thickness, uniformity and concentricity. Thus there is less imbalance for the centrifugal force to act upon. There is some imbalance which is why the accuracy is 1 moa instead of just one hole. But the less imbalance in the MK bullets means the center of spin with be closer to the center of form which means better accuracy. There is a very good explanation of this in Hornady manuals which include pictures.

Bottom line; very imbalanced bullets which are very inaccurate can be very stable in flight. Thus do not confuse a bullets stability for accurate flight with the RPM threshold (affect of centrifugal force on the bullets imbalances) as the two are completely different aspects of exterior ballistics.

Larry Gibson

[Larry Gibson]

Larry did you complete the test?

Yes, I did complete the tests. I am now shooting 2600+ fps with and average of 1.5 moa (with 10 shot groups) out to 300+ yards with the 14" twist Palma .308W rifle and the 311466 bullet. Recently a forum member, Scharfscheutzer, was visiting and was hitting a 2x4" piece of asphalt on the 300 yard berm every shot using the Palma rifle and that load. I adjusted the T16 scope up 5 1/2 moa from the 100 yard zero and fired 2 foulers both of which hit the asphalt. I turned the rifle over to him and he was right on.

Can't do that with my 10" twist or 12" twist .308Ws rifles for the obvious reason that at 2600 fps the 10" twist is cranking 187,200 RPM. The 12" twist rifle at 2600 fps is cranking 156,000 RPM and the 14" twist rifle at 2600 fps is cranking 133,714 RPM. Obviously the centrifugal force is acting less on the bullet out of the 14" twist rifle.

Some do not want to believe the RPM threshold is real, especially with naked cast bullets, but the proof is there at the point where accuracy is lost at HV.

Larry Gibson

[44man]

I believe lack of spin results in lack of accuracy. However too much spin will also result in loss of accuracy. During my Hunter BR shooting days my spin thoughts were seriously bent. This is with jacketed bullets of course. I started out with a 15 twist and 125 gr. bullets in a .30 case (wildcat) slightly smaller than the parent .308 and worried about stability. As the years went by, the winning shooters changed to a 16" twist and then to a 17" twist. Lower spin increased accuracy. Clearly there is a spin that is best. Below spin rate accuracy goes to hell, and accuracy above that spin decreases, but stays good, although not good enough to win. Bullet weights depended upon shooter and his/her mood at the time but generally were in the 125 to 135 gr. range with .30 cal cartridges of one flavor or another, but all were slightly smaller than the .308 Win.. Remember the standard .30 cal. twist is 10" !! The targets were at 100, 200, and 300 yards so "close range" is a relative thing. FWIW Pilgrim
You have seen it. But a 125 gr in the .30 is so different. You get to a high enough velocity with a slow twist. Ever try a 200 gr?
Like my old .220 Swift, never shot to an inch at 100 yards but after the bullet went to sleep I shot 5 in 1/4" at 350 yards. I sighted at 350 and head shot chucks over 600 yards but could miss one at 100.
A slow twist, close range rifle will shoot great at close range but spin is just not enough way out. Like the .44 mag Marlin, shot OK at 50 but a slingshot at 100.
If you over spin you can reduce the velocity but if under spun you can't add enough powder.
I much prefer over spinning in any case.
Remember the .244 Rem? Had a slow twist for high velocity varmint bullets, but the .243 had faster and could shoot deer bullets so it won the race. The .244 was superior in every way and could have had a twist change for the use of the caliber. Deer gun, one twist, varmints another.
Like a .454 in a 2" barrel that you think will shoot the same as from a 10" when you can not get the velocity or shooting a heavy boolit from a .45 Colt from a 1 in 24" instead of 1 in 16". Need almost 60,000 PSI from the 1 in 24".
The .222 and .222 mag were both better then the .223 but it was twist that determined the bullet. Now twists have been made FASTER. As bullets get heavier, the twist is increased.
Twist rates have put more calibers in the graveyard then anything else.
Larry has a tough task with no real answers. Nothing in the end to be of help.
I am sorry but there is no way to compare a boolit from all twist rates with the same loads.

[Larry Gibson]

Same old non believing arguments from 44man. Not a tough task at all as it is done. The answers are real and they are there.

I am sorry but there is no way to compare a boolit from all twist rates with the same loads.

Now that is a "limit" on ones self. It is very easy to do; have different rifles with different twists chambered to the same cartridge. Yes, we've all heard the "oh the barrels are different" argument before. What you all, who make that argument, fail to understand (especially the self proclaimed engineer educated ones) is that such comparisons are made all the time in many different things.

For an accurate comparison of "accuracy gain/loss" in this particular case (3 rifles of the same cartridge with different twists) the gain/loss is not compared to the 3 rifles together but simple as individual rifles. For example; if a 10" twist rifle is capable of 1/2 moa accuracy, the 12" twist is capable of 1 moa accuracy an the 12" twist capable 1 1/2 moa accuracy we have a basis to make a comparison of gain/loss of accuracy of each rifle. If the 10" twist rifle begins to lose accuracy at 2000 fps with the same load and the 12 and 14" twist do not it is telling us something. Then if the 12" twist begins to lose accuracy at 2350 fps it also is telling us something. And when the 14" twist begins to lose accuracy at 2650 fps it to is telling us something. It is the velocity at which each rifle lost accuracy that is the point. It is not a comparison of groups sizes between the rifles.

Understanding how analytical testing as such is done we then understand that the RPM at which each rifle lost accuracy was in the 135-140,000 RPM range.....the top end of the RPM threshold.

I a recent thread geargnasher hit what he called a "wall" just under 2400 fps with the tricked out 30x57 rifle goodsteel built for him. This was in spite of all the care taken to make sure everything in the rifle was concentric,, the cartridge was excellent for cast bullet use (I designed it), the bullet was an excellent design and geargnasher loaded it with all due care and proper procedure to ensure it was as aligned in the bore as concentrically as possible. So why did the cast bullet in hit a "wall" at just under 2400 fps and not maintain accuracy to well beyond 2800+ fps for which that cartridge was designed? The reason is simple; geargnasher chose to use a 12" twist barrel. And just where is the top end of the RPM threshold for a 12" twist barrel with a cast bullet? Just under 2400 fps is where. Had gearganasher used a 16" twist barrel he would be seeing the full capability of the cartridge with cast bullets. Had he even used a 14" twist barrel he most likely would be pushing 2600+ fps before coming against the "wall". Instead he chose the 12" twist barrel and found the "wall" just where it is supposed to be......just under 2400 fps.

One last point 44man, you are still arguing and using bullet stability as points of disagreement. No disagreement from me at all on those points except they have nothing to do with the RPM threshold and the topic of the thread. Ergo, your arguments are moot because they are not to the point.

Larry Gibson

[7br]

I am not very smart so please type slowly and use small words. If we are operating under the assumption that there is a rpm limit for conventional (gas-checked, lubed, not paper-patched) bullets, what is causing it?

If it is the centrifugal forces acting on imperfections, why wouldn't paper patched bullets be affected in the same manner. The only explanation I can see for this would be that additional imperfections are added to the conventional bullet somewhere between when the bullet starts to move out of the case until it exits the muzzle. This might be caused by the paperpatch supporting the nose so it does not slump as much. It might be that the paper patch is helping the bullet engage the rifling in a manner that does not deform the bullet. What would happen if we put a gascheck on the nose of the bullet to engage the rifling in the hopes of the check handling the rotational stresses better than straight lead?

Could it be from lube purging?

Final question: Does a paper patch stay on the bullet all the way to the target?

[kevmc]

I'm new to this thread......but, I've read every post from start to finish.
I understand what Larry was endeavoring to do, and I commend him for a well thought out test of HIS idea/question!!

To the others who thought he should have done this or that.....have at it.

[cainttype]

Like my old .220 Swift, never shot to an inch at 100 yards but after the bullet went to sleep I shot 5 in 1/4" at 350 yards. I sighted at 350 and head shot chucks over 600 yards but could miss one at 100.

Please excuse the brief hijack, but after many years with many firearms (of all sorts), I've never witnessed the "sleeping bullet" behavior. I've heard of it for as long as I can remember but I've never actually encountered it, personally. Friends that mentioned it in the past could never reproduce the phenomenom in front of me, so I'm pretty skeptical about it's occurrence happening with any regularity.
I am in no way attempting to question your veracity, 44man, but that scenario is far more difficult for me to accept than the methodology being used by LG in this instance.

I don't see a problem with Larry's test results, for each of the rifles he used. As he has clearly stated several times, each rifle was tested individually, against itself.
No rifle mentioned is being "tested" against any other rifle... Each rifle established it's own benchmark. Loads were then ladder tested until the same rifle began to show deteriorating accuracy... That's exactly the same methods used by most experienced shooters on this forum, HV or otherwise.

Being more of a low-medium velocity cast rifle shooter and any sort of handgun, the quest for HV is pretty much academic for me. That said, every tidbit of insight gathered and shared by guys like Larry is much appreciated.
If anyone disputes the concepts suggested here, by all means, please present your own findings. Hopefully you can provide the details and describe your methodology and reasoning as succinctly as he has.

[7br]

Please excuse the brief hijack, but after many years with many firearms (of all sorts), I've never witnessed the "sleeping bullet" behavior. I've heard of it for as long as I can remember but I've never actually encountered it, personally. Friends that mentioned it in the past could never reproduce the phenomenom in front of me, so I'm pretty skeptical about it's occurrence happening with any regularity.


If I remember correctly, the effect is called precession. Basically, think about a top when you were a kid. When you first start spinning it, it spins on its axis. The nose of the top will generally trace something like a circle on the flat surface it is spinning on. As it slows down, the top zeros in on the center of the circle the nose has been tracing. It will hold pretty stable for a while as it slows down, and will finally go unstable and fall over.

I do not have access to a range long enough to prove or disprove whether or not it happens, but I have heard that the .50 bmg rifles do exhibit this behavior.

[Larry Gibson]

Like my old .220 Swift, never shot to an inch at 100 yards but after the bullet went to sleep I shot 5 in 1/4" at 350 yards. I sighted at 350 and head shot chucks over 600 yards but could miss one at 100.

Not questioning 44man's veracity with such but the example given references bullet stability and the supposed reduction of group size when the initial yaw evens out. I also have never seen nor had this phenomenon of rifles shooting smaller groups at longer ranges, especially when the sample size of the "group" is sufficient to establish a reliable measurement of accuracy. My point in quoting 44man here is as mentioned in my previous post; he is not referencing the RPM threshold nor the adverse affect of centrifugal force on the bullets and as such his example is "moot".....basically meaningless in context to the subject.

Larry Gibson

[cainttype]

If I remember correctly, the effect is called precession.

The top lands unbalanced, but gyroscopic forces induced by the rapid spin stapilize it into the upright (stable) postion... but does the top always stabilize at the exact same spot on the floor?

I have no issue with the 50 BMG, or any other projectile (including artillery) leaving the bore spinning slightly off axis and increasing the apparent diameter of a measured group as it stabilizes. Those elongated holes begin to round out as that happens.
My difficulty is the "sleeping" phenom where a stable, properly oriented projectile gains accuracy as ranges increase. In the preceeding example, accuracy results dramatically increased from 100 yds to 350.
I have never witnessed such behavior. I won't claim it doesn't exist, because I don't know that as an absolute. I do know that I've never seen it, in person. I've also heard the talk, but as of yet nobody has been able to reproduce anything but short-range yawing that demonstrated elongated holes. I've never witnessed long-range accuracy improvements after a "sleeper" woke up.

I am, as stated, much more interested in Larry's experiment. I'll be following any recent posts here, hoping other members with some input about pursuing HV with these different twist rates have fared.

[45 2.1]

My difficulty is the "sleeping" phenom where a stable, properly oriented projectile gains accuracy as ranges increase. In the preceeding example, accuracy results dramatically increased from 100 yds to 350. I have never witnessed such behavior.

I believe if you talk to the long range BPCR folks, they can enlighten you about that.

I am, as stated, much more interested in Larry's experiment. I'll be following any recent posts here, hoping other members with some input about pursuing HV with these different twist rates have fared.

Lots of posts on that... research the Archives. Currently, the subject generates too much heat with little light transmitted to do any good here.

[mainiac]

I believe lack of spin results in lack of accuracy. However too much spin will also result in loss of accuracy. During my Hunter BR shooting days my spin thoughts were seriously bent. This is with jacketed bullets of course. I started out with a 15 twist and 125 gr. bullets in a .30 case (wildcat) slightly smaller than the parent .308 and worried about stability. As the years went by, the winning shooters changed to a 16" twist and then to a 17" twist. Lower spin increased accuracy. Clearly there is a spin that is best. Below spin rate accuracy goes to hell, and accuracy above that spin decreases, but stays good, although not good enough to win. Bullet weights depended upon shooter and his/her mood at the time but generally were in the 125 to 135 gr. range with .30 cal cartridges of one flavor or another, but all were slightly smaller than the .308 Win.. Remember the standard .30 cal. twist is 10" !! The targets were at 100, 200, and 300 yards so "close range" is a relative thing. FWIW Pilgrim
Yup,,,I shot ibs hunter br for quite a while myself. The standard was 308win/168 sierra/14 twist barrells.Then,them PA boys started shooting bullets made on the short jacket,and started using 15,then 16,then 17 twist barrells,with the 1.080 jacket.Them guns kept shooting tighter and tighter.I havent shot that game for 10 years,,wouldnt surprise me if they was using 20 inch twist barrells,with 80gr bullets,in the .30cal, now a days!!!

Over twist a bullet,and accuracy degrades,

[Larry Gibson]

7br

Had an answer but can't now connect to forum from my PC. Perhaps I have been discomboomerated from the forum?

Larry Gibson

[cainttype]

My difficulty is the "sleeping" phenom where a stable, properly oriented projectile gains accuracy as ranges increase. In the preceeding example, accuracy results dramatically increased from 100 yds to 350. I have never witnessed such behavior.

I believe if you talk to the long range BPCR folks, they can enlighten you about that.

I am, as stated, much more interested in Larry's experiment. I'll be following any recent posts here, hoping other members with some input about pursuing HV with these different twist rates have fared.

Lots of posts on that... research the Archives. Currently, the subject generates too much heat with little light transmitted to do any good here.



I do have friends heavily involved in BPCR, and we have discussed the issue at length. Like I said, no one has conclusively demonstated the "sleeper" phenom as of yet, let alone it's repeatability on demand.
I stay open-minded about the possibility, but I haven't witnessed proof enough to verify it as anything other than coincidence.

I have read plenty of archives, it was there that I originally found this thread.
The specific input I'd like to see is from others currently experimenting using slower than standard twist rates because of the arguments and differing viewpoints this subject has given rise too in the past.
The question of reaching higher velocities through proper fit, advanced load development, and firearm quality has never been the issue. The real question is whether a slower twist is an advantage.
If the HV enthusiasts here find it easier to achieve 2500+ fps with a 1-in-14" twist instead of a 1-10" (for example), the obvious answer would be, "Yes. It helps."

[44man]

To answer a little more about the going to "sleep" bullet. The bullet does not yaw or make sideways holes. It just rotates around the flight path. It can be seen with a good spotting scope and a S&W 29 shooting 240 gr or lighter bullets. What happened with the S&W was it was accurate doing 1/2" at 50 meters but as distance changed the POI would vary on the target depending on where the bullet was in the corkscrew.
Yeah, yeah, I know, nobody can tell that with a revolver!
A rifle like the swift is in the 3800 to 4000 fps range, spin is out of sight. I never liked the 22-250 because it only liked lighter bullets while my swift shot the 60 gr Hornady. The difference was twist.
The precession is why a slower twist is better at close ranges.
BPCR rifles also suffer from a too slow twist for the velocities obtained. I watch it with a heavy boolit through a scope when a boolit goes off course so far downrange.
I do see what Larry is trying to do but his list is still going to be at what velocity each twist rate reaches instability.
What is hard to imagine since everyone wants max velocity is that if the twist is fast, you just reduce the velocity a little but if too slow and you are at max already, what do you do? You change the boolit/bullet is what.
It is true that over spin can also reduce accuracy but the problem is easy to fix.
Just try to get accuracy with a long boolit in a ML with a 1 in 60 to 66" twist. Try to shoot a RB from an inline 1 in 28".
You can shoot a heavy boolit from a Ruger .45 Colt with 1 in 16" but NOT from a Freedom with 1 in 24". The Freedom needs a lighter boolit.
It is the same thing all the time though where someone will say they get good accuracy, define accuracy to me.
You see 25 yard groups shot all day with revolvers but hey, I got better at 500 yards.
My question to Larry is what distances will be shot for the testing. How will you find what the boolit does from 50 to 500 yards?
My favorite saying is a WFN will not shoot past 50 yards. GRIN!
Larry might find a threshold at 100 yards but does not know if the boolit will go to "sleep" at 200.
This crazy old coot will continue to rain on parades. I just love the Greenhill formula too!

[44man]

Look at it from my point with the Swift. Had I got 1/4" at 100 yards, I would NOT be able to shoot 600 yards. Longest shot was a head shot chuck at 620 yards.
My friend has the .50 BMG and it just sucks at 200 yards. Comes to life at 1000.
To find a threshold at one distance with a boolit is the "moot" point.
Larry, how do you know what the boolit will do at other distances? Will you extend testing at very long ranges? Got enough money?

[45 2.1]

It takes a heck of a lot of shooting... with cast, not jacketed, to see quite a few of these things. Some have already did it and some need to shoot some more to experience it. There are several divergent methods to achieve results, not just one.

[cainttype]

sgt.mike, I'd add Bryan Litz to the reading list along with Dr. Mann.
The problem I have is not that a bullet exiting the muzzle pitching and yawing can stabilize during it's flight path. In that case, pre-stabilized groups could easily show a more rapid shot dispersion tendency at closer range. After the bullet stabilizes, however, is it possible for accuracy to actually improve as ranges increase? The MOA calculations could show an improvement comparing pre-stabilized to after stabilization, but would "more accurate" be the proper way to describe what happened?...Example; If the sleeper can't shoot into a 2" circle at 100 yards, is there any chance of shooting into 2" further downrange?
If our sleeper stabilizes at 100 yds, and we use our 100-200 yd results as our baseline, could we ever expect to see accuracy improvements downrange?
My expectation is that after the bullet stabilizes there will be no improvement. I'm completely open to seeing evidence proving otherwise, but I haven't witnessed it yet.

[44man]

sgt.mike, I'd add Bryan Litz to the reading list along with Dr. Mann.
The problem I have is not that a bullet exiting the muzzle pitching and yawing can stabilize during it's flight path. In that case, pre-stabilized groups could easily show a more rapid shot dispersion tendency at closer range. After the bullet stabilizes, however, is it possible for accuracy to actually improve as ranges increase? The MOA calculations could show an improvement comparing pre-stabilized to after stabilization, but would "more accurate" be the proper way to describe what happened?...Example; If the sleeper can't shoot into a 2" circle at 100 yards, is there any chance of shooting into 2" further downrange?
If our sleeper stabilizes at 100 yds, and we use our 100-200 yd results as our baseline, could we ever expect to see accuracy improvements downrange?
My expectation is that after the bullet stabilizes there will be no improvement. I'm completely open to seeing evidence proving otherwise, but I haven't witnessed it yet.
Depends on caliber and velocity, bullets don't go to sleep at 100 unless twist is slow, you might not see sleep until 400 yards or so. Only over spin conditions show it anyway so don't look for much in common deer rifles. Most everyone uses 100 yards to search for accuracy, that is fine for most conditions and hunting. I spent many, many years varmint hunting and shooting extreme ranges. I would see a chuck or crow at 200, turn and walk another 200 the opposite direction before shooting.
If you reach stability, the good group at 100 will also be good at range but other factors are in play too. Paper figures will not help or solve it.
Bullet drop is another thing, I shot for drop, I put a target at 100, 150, etc to 600 yards, shot at each. Adjusted and wrote the settings on paper on the side of my scope. It was easy to click the Balvar 24 scope to the range as I knew the field lengths. I take a 3' pace and will only be a foot off at 200 or 300 yards measured. I am as accurate as the laser range finder.
Up and down mountains is not for pacing distance, need flat land like northern Ohio.
Can a 2" at 100 shoot better at 400? Yes it can if over spun at 100. Proper spin at 100 will show an increase in groups as range extends so expect 1" at 100 to be 2" at 200. That is normal. if you get 1" at 100 and 5" at 200, you are under spinning.

[popper]

Just got to show my un-intellegence here. Will a boolit 'go to sleep'? Yup. Will you notice it? Probably not. Shot enough self propelled vehicles that left smoke trails to observe it. The transonic velocity region is a lot wider than you guys think. A lot of stuff happens in that region.

[44man]

It takes a heck of a lot of shooting... with cast, not jacketed, to see quite a few of these things. Some have already did it and some need to shoot some more to experience it. There are several divergent methods to achieve results, not just one.
The difference between cast and jacketed is very small but jacketed will take rifling right now while a poor cast might take half the barrel length. So let us say a boolit skids like mad once pressure gets too high, would anyone call that an RPM threshold? Say the boolit slumps into a blob, is that an RPM threshold. What if lube fails?
The problem is not cut and dried and there is no easy answer. You just have to see what you can do.
Larry will NEVER be able to do all the testing needed. All of us combined are a drop in the bucket. I have fooled with this for over 60 years and understood twist as a punk while many still can't get it right today.
There is no way to shoot the same load from different twist rates because you will find the "Threshold" with the first groups.
I never found the pot of gold at the end of the rainbow because the leprechaun does not exist. But I do find what a gun likes.

[45 2.1]

The difference between cast and jacketed is very small but jacketed will take rifling right now while a poor cast might take half the barrel length. So let us say a boolit skids like mad once pressure gets too high, would anyone call that an RPM threshold?

It always amazes me how little is known about alloys and their ability to perform correctly at different pressures. Use the right one and none of that crazy stuff happens. Pick the right powder combination and you can do things not considered possible. All depends on how good your picker is.


44 Man do you mean what you wrote or that you can't obtain the same velocity with the exact same load in three different twist?

Hmmm......... You can't even do that with three consecutive matching rifles off the makers line, let alone three different rifles that have different twists let alone different harmonics........ TOO MANY VARIABLES TO CHASE.

[Larry Gibson]

Not ignoring the questions. Only have access to site via smart phone right now. It's not conducive to answering.

Larry Gibson

[cainttype]

Exactly the projectile shoots X " group at X range then at X range the projectile still Shoots the same X" group hence the MOA just reduced (that is the observation method or my third grade answer) or another explaination is the nutation effect is smaller because of Velocity and RPM reduction coupled with the effects of drag hence the projectile is more dynamically balance nutation and yaw along it's established center line of axis and maintains it's pre determined cone of placement (that was the 12th grade answer).

The answer above makes no differance if cast or jacketed it is just a matter of what RPM /Velocity that it happens based on materials/construction/mass etc etc.....




:popcorn: now I'm waiting on the flames and attacks:dung_hits_fan:


I try to keep an open mind, but the rifle/load combo that can consistently shot into a 2" circle @ 400 yards and can not shoot into a 2"circle @ 100 yards has not crossed my path, yet... I'll be happy to admit when it does, but I will not lose sleep waiting on it.
As outlined clearly in SEVERAL previous posts, a reduction in calculated MOA, or cone of fire probability, after a bullet "wakes up" is not what I'm questioning (perhaps we should use our post-graduate gorilla here).

I'm still waiting for input from anyone else using slower twist rates in the pursuit of higher velocity cast rifle, standard grease-groove bullets.
The simple question posed earlier was whether they found it "easier", on average, to reach higher velocities while using slower twists (1 in 14" compared to 1 in 10", for instance)... I suspect the answer is "yes", but I'm waiting for their opinions.

[runfiverun]

Larry is having I.P. address problems right now, give him/willy a chance to get things straightened out.

[44man]

It always amazes me how little is known about alloys and their ability to perform correctly at different pressures. Use the right one and none of that crazy stuff happens. Pick the right powder combination and you can do things not considered possible. All depends on how good your picker is. (quote)
True but Larry seems to have chosen one alloy. Should the tests be carried out with every alloy instead? That should add a million more shots! Somewhere along the line an alloy failure can lead to wrong conclusions.
I appreciate what Larry is trying to do but see too many variables, any one of whitch can skew results. He is starting a task I would not want to try.

[44man]

44 Man do you mean what you wrote or that you can't obtain the same velocity with the exact same load in three differant twist?
Not nit picking here or anything, but I can shoot the exact load in any twist weapon that I choose. But My Velocity will change based on twist rate the faster the twist the slower the MV for a given powder quanity behind a given projectile.
Just trying to understand where your going.


( or was the rule of thumb for jacketed the faster the twist the faster the MV, I think I got it correct above for Lead though)
Not what I said at all! Even if you got the exact same velocity from all the guns, the twist will change the spin rate. Since two guns with the same rate can have different velocities due to production tolerances. Let us say you get X velocity from one but another twist gun has a different velocity from dimensions alone and also reaches stability at the velocity it shoots at, you can not say twist is the cause. It only means the second rifle has reached stability because the velocity is different then the first. I doubt very much a twist change alone will affect velocities. You just have a different gun.
This is a can of worms that should not have the lid removed.
Larry must have every rifle shoot the exact same velocity with the exact same pressure.
45 2.1 is correct, you can NOT shoot the same load from every rifle you choose or any twist rate.
The list of variables would take pages and pages and I don't even want to think of making a list.

[swheeler]

By all means carry on Larry, I want to see the results.

[44man]

Step into the revolver world a little. Take a .454 with a 1 in 24" twist using a 335 gr+ boolit. It will shoot but what about a .45 Colt with a 1 in 24 rate? Cant be done unless you exceed .454 pressures. It is the reason the Colt usually has a 1 in 16" twist so you can shoot slower and find stability. What do you do with the .45 and a 1 in 24" rate? you use lighter boolits. You need more velocity.

[45 2.1]

True but Larry seems to have chosen one alloy. Should the tests be carried out with every alloy instead? That should add a million more shots! Somewhere along the line an alloy failure can lead to wrong conclusions.
By golly, you do see a few of the problems associated with this. Picking the right alloy for the pressure/time curve involved is one of the questions that haven't been answered yet.

I appreciate what Larry is trying to do but see too many variables (yep, quite a few of them), any one of which can skew results. He is starting a task I would not want to try.
Multiple variables skew results every time.

[Larry Gibson]

Trouble with the last two posters is they are stuck in and on interior ballistics. The RPM Threshold happens during exterior ballistics. It happens to stable bullets. If the same bullet comes out of the 3 barrels with different twists at the same velocity then we have an accurate comparison of the difference each twist has on the bullet in flight at that velocity/RPM.

We all already know the difference in the internal ballistics. This has been gone over many times and they still haven't gotten it. Equalise the velocity with different twist barrels and the difference is RPM. It's that simple boys.

Larry Gibson

[btroj]

If the threshold is entirely exterior ballistics how can it be "moved" by changing powder speed or alloy?
You state that the threshold isn't a limit but rather a point where accuracy becomes more difficult to attain. If the threshold is entirely external ballistics then wouldn't it be a hard limit?

I think alloy, pressure curve, and bullet design all have a huge role to play in accuracy at higher velocities. It is about finding balance within a system of variables.

Thus those RPM threshold figures are not hard and fast as some things like a too soft alloy or too fast a powder can lower the threshold. Conversely, other things like a harder alloy or a slow burning powder can raise the threshold.

[Larry Gibson]

Btroj

How many times must it be explained. Slower powders are used to slow the time/pressure curve to lessen the imbalance done to the bullet during acceleration which is in the internal ballistics phase. During the external ballistics phase the centrifugal force acts on those imbalances. At a certain level of RPM the centrifugal force causes accuracy to deteriorate rapidly. That is the RPM Threshold of that bullet with that load out of whatever twist barrel is used.

It does not adversely affect the stability of the bullet as a few of you seem fixated on.

Larry Gibson

[btroj]

Btroj

How many times must it be explained. Slower powders are used to slow the time/pressure curve to lessen the imbalance done to the bullet during acceleration which is in the internal ballistics phase. During the external ballistics phase the centrifugal force acts on those imbalances. At a certain level of RPM the centrifugal force causes accuracy to deteriorate rapidly. That is the RPM Threshold of that bullet with that load out of whatever twist barrel is used.

It does not adversely affect the stability of the bullet as a few of you seem fixated on.



Larry Gibson

The portion in red in my post is taken directly from your first post in this thread. Your words.

Changing alloy and pressure curve are purely internal ballistics and YOU say those things can move the rpm threshold.

Now you seem to be saying that "a few" don't understand that the threshold is all about external ballistics.

Which is it?

Personally I think it is silly to try and remove one from the other. Everything we do to a bullet in the barrel has an effect on it once it leaves the barrel.

As for changing pressure curve not affecting bullet stability, what? So a bullet that is damaged during the ignition and pressure rise isn't less stable than one launched with little to no deformation?

If the pressure curve is irrelevant, as you seem to be saying, then how can it possibly be used to move the threshold?

If the threshold is entirely about external ballistics then for a single bullet it would be a hard limit. Bullet can't be changed, rpm is purely velocity/twist related so at a certain velocity accuracy detonates. Period.

Problem is we know that isn't the case. You yourself said we can move it. We can move it by altering interior ballistics. Those interior ballistic changes all have one effect, reducing damage to the bullet during it's time in the barrel.

Are you saying that what we do to the bullet n the barrel has zero effect on the threshold? If not then in what way are people stuck on interior ballistics? If they matter then shouldn't we be fixated on them?

[Digital Dan]

http://img.photobucket.com/albums/v298/muddler/Trip/IMG_2849_zpsf0e2ab4d.jpg (http://smg.photobucket.com/user/muddler/media/Trip/IMG_2849_zpsf0e2ab4d.jpg.html)

[44man]

Remember the Juenke system? A little machine to check bullet out of balance. I understand some of the better bullet makers still use it to test lots.
However it won't work on cast. I can't even use my run out tester on the boolit, need to measure case necks. Just too hard to have a round boolit, then there is the parting line.
The amazing thing is that we get cast to shoot as good or better then jacketed. I get superb accuracy from revolvers with bullets and just using the same techniques with lead, it has proven very easy to match groups.
It has also proven that the faster twists of BFR's can not be matched.
To stray to stuff like too soft lead has been nothing but failure, Soft throwing fliers from boolit damage and ruining fit. To use an "M" die to prevent boolit sizing while ruining tension is a failure.
The FCD is a failure as is any over crimping.
Yet all you will read is to make the boolit softer or to crimp the devil out of it. My premise was to duplicate jacketed in every way.
What it came down to was interior ballistics, boolit integrity and letting the boolit be the guide into the bore and reaching the spin a boolit needs.
A gun needs a boolit at the right stability and adding more velocity over that results in groups opening. Cast works the same as jacketed so let us say you shoot jacketed at 2700 fps from a certain twist, can you use the same rate to shoot that bullet at 3800 fps? How about 900 fps?
Once you change the twist or velocity with cast, accuracy will go away so there is nothing to measure beyond the stability point, the threshold is that point only for a given boolit in a given twist. You exceed it with any change.
The only thing to be found is the range a boolit can be shot from a certain gun or what velocity is needed for a range of boolit weights. Each will need a different load but is far easier then trying to make one boolit do what it can't.
I never found pixie dust to make a boolit go faster or slower then stability.
Garbage in, garbage out!

[grouch]

I'd still like to hear Larry's results.
Grouch

[Larry Gibson]

I believe this site is hacked. I can't post from my PC or 2 laptops. Can only post from smart phone so posting is limited. Appears my IP is blocked.

Larry Gibson

[Larry Gibson]

I'd still like to hear Larry's results.
Grouch

PM your email and I will show you results.

Larry Gibson

[Larry Gibson]

As to 45 2.1, Byron and now 44man; same old arguments and erroneous assumptions over and over. Old Indian say; waste of arrow to shoot at buffalo already falling off cliff. ...........I'm tired of wasting arrows. Instead of arguing simply because my name is on the post or hypothosizing non relevance try conducting the simple test with a 30-06 that I've mentioned numerous times. You will find the RPM Threshold.

Larry Gibson

[btroj]

Jay Carney couldn't have said it better

[cainttype]

"I must be missing something.
Larry has attempted to illustrate through multiple posts, for a long time, that this "RPM threshold" is an area where average cast shooters, using average firearms, and employing basic loading procedures are likely to see a deterioration of accuracy as velocities are increased if the standard grease-grooved cast projectile exceeds 140,000 RPM. He has, as far as I'm aware, always maintained that this "threshold" is NOT a limit, and can be exceeded by various means...better casts, better loading techniques, better component choices, better firearms, and better ammo-to-firearm fit.
The theory didn't originate with Larry, as he has explained before, but he has done some serious testing that has obvious interest to the average cast rifle shooter. The simple point that it is EASIER to achieve accuracy with higher velocities by using a slower rate twist is very important to the casual shooter who has no desire to get terribly technical, but likes to enjoy his firearm with a minimum of fuss.
I very much appreciate anyone that takes the time to methodically test anything that interests me and shares their results. Whether I agree with their conclusions is irrelevant, I appreciate their generosity.
By the way, Larry, you're welcome to shoot with me anytime, as are any others that even attempt to dessiminate information in an effort to help others."


That was posted 01-08-14... Six months ago.
Nothing has changed. Larry attempts to offer results of pretty well documented tests that he's conducted himself. All the while, being taken to task by others that have yet to answer a simple question I've asked several times ( except 44man, who has stated his position)... So I'll ask AGAIN.... Has anyone else tried to use slower twist rates in an attempt to achieve higher velocities, while maintaining accuracy, with standard grease-groove cast bullets in rifles, and did you find it to be an advantage?
Larry details the non-linear accuracy results that occur whenever the "threshold" of a given load has been pushed too far... Has anyone else done the testing on their own to look for these signs?

I hear, and have heard, the dissenting yammering. As of yet, what I haven't heard is anyone else detailing their own trials.
I already know there are those of "us" (whoever that is) that have seen it all, done it all, and know it all, but I'm not aware of anyone that tries harder to help and mentor members on this site than Larry Gibson.
Thanks, Larry... I count you as a friend.

[Newtire]

It is pretty disappointing to see an interesting study about to take place by someone who's trying to help us along as a group by perfoming a series of time consuming tests being sniped at. Fer crissakes guys, let the guy get off the ground and go do his test and come back, turn in the "flight report" and hear the findings. If you feel so adamant that someone is wrong, go out and make your own experiment and then compare results.

It is what it is, sure there are vaiables-from what I gather, this is what the test is trying to find out isn't it?

Larry's always done some pretty straight up kind of reports. Let the guy get off the runway before you try to shoot him down.

It's easy for someone to sit behind a computer keyboard and theorize. Larry's going to get up, go out and shoot some boolits. There's a big difference.

I'm interested in the "Real Deal". Nuff Said.

[waksupi]

It is pretty disappointing to see an interesting study about to take place by someone who's trying to help us along as a group by perfoming a series of time consuming tests being sniped at. Fer crissakes guys, let the guy get off the ground and go do his test and come back, turn in the "flight report" and hear the findings. If you feel so adamant that someone is wrong, go out and make your own experiment and then compare results.

It is what it is, sure there are vaiables-from what I gather, this is what the test is trying to find out isn't it?

Larry's always done some pretty straight up kind of reports. Let the guy get off the runway before you try to shoot him down.

It's easy for someone to sit behind a computer keyboard and theorize. Larry's going to get up, go out and shoot some boolits. There's a big difference.

I'm interested in the "Real Deal". Nuff Said.


Thar ya go. He's putting up. If you're not, shut up.

[freebullet]

I read through 10 pages of attacks and disputes with no test results. Frankly, had I gone through what Larry has in this thread I doubt I would post the results here either.

[MBTcustom]

There was a time when this site had more than it's fair share of people who were already busting caps and throwing away lead, who just wanted to talk about the way they saw the results.
Now it seems that if anybody actually plans to do any shooting/experimenting they get piled on by a whole herd of people who never posted a group on this forum, and who don't help anybody but themselves (rather generously to the service we provide) and they pile on anyone who doesn't think about this sport in exactly the narrow way that their mind is capable of comprehending.

I also want to hear what Larry has to say (matter of fact, I was going to do almost exactly the same thing till I found this thread!).
Larry has a different way of looking at cast boolit shooting. A different gauge. If you just can't stand the idea of some guy on the other side of the country who likes to measure his cast boolit success with RPM instead of FPS, then go find a place where everybody thinks exactly like you do.

Larry, if you need a cast boolit gunsmith to help you eliminate a few more variables, you've got my number. I know a lot more about building them than shooting them.
If you decide it's just too big a headache to continue, let me know. I'm going to see this done one way or the other.
I don't see any other threads here comparing the effects of different twist rates side by side, and I don't see anybody else stepping up to the bar.

Yes there are different variables with each barrel. Does that mean there is nothing to learn by running a test like this? Gimme a break fellers! I learn something with each individual boolit I send down range! In fact, I learn more from failure than I do from success. Crawl out of your rut and open your mind a little! You might not agree with the method, the results, or the conclusion but you might just learn something and apply it to your way of doing things.

What really bugs me about this thread is, I really don't think anybody is afraid Larry is wrong and wasting bandwidth. I think that people are afraid he might be right, and they would rather silence him than consider the possibility that everything that can be learned has not already been learned by (pick your guru).
Wake up and smell the coffee! This is how the old shooters found out what they did. There was a time, if you told people that you: cast your boolits oversize, fit them to the throat, let them sit for 2 weeks before loading them, make your own lube, use aluminum gas checks that don't crimp on, or use jacketed load data, you would be laughed off the range and called a moron and a weirdo. Now we all so these things because somebody took the time to fix "a problem that didn't exist".

Surely if we can have a thread that deals with purple font, or thread killers, then we can have a thread that deals with a subject like this!

[Love Life]

A man on another forum ran a test with 4 different 6mm cartridges, but all the barrels were cut from the same chunk of steel.

If a call to bartlein can be made, and they can cut 3 different 30 cal twists into 3 different barrels from the same chunk of steel, then I will buy one of the barrels for this experiment and pay to have it chambered and mounted to the test rifle.

[MBTcustom]

A man on another forum ran a test with 4 different 6mm cartridges, but all the barrels were cut from the same chunk of steel.

If a call to bartlein can be made, and they can cut 3 different 30 cal twists into 3 different barrels from the same chunk of steel, then I will buy one of the barrels for this experiment and pay to have it chambered and mounted to the test rifle.

You won't pay much if it's heading my way.
BTW, Green Mountain has barrel blanks in 8, 10, and 12 twist for $100 each. That was going to be the direction I was going to go. Straight profile, no taper, reamed matchgrade 308 to exactly the same headspace, Bluprinted action for all three to be tested on.
Yeah it would be nice if they made a 14 twist also, but hey, beggars can't be choosers.

[Love Life]

3 Barrels cut with the same reamer to the same specs ought to show a bunch of things. I might even have an action around you can use. I won't do the testing though because I am knee deep in other stuff right now.

Here is a good chance to solidify some things, and at the end of the day I'll still have a barrel to play with.

I'll shoot you a PM.

[Terrence Clarke]

Hi Larry,great post,look forward to the test result. I agree with your RPM limit on cast bullets, but my own tests have shown a lower rpm limit for best results. I wonder what effect different number of grooves in the barrel have, if any on the RPM and accuracy of cast bullets,keep up the good work.

[PAT303]

Goodsteel,I like your post,there's people on here,one in particular who does post unbelieveable groups and performances from rifles but as yet I've never seen a group posted ever,the same person does reply,usually by being critical of others and then gives replies that make no sense what so ever.I'd like Larry to just get on with and leave the criticism unless they proove otherwise,I will hopefully be doing a grease lube dry lube comparison thread soon,it takes alot of work and will be ignoring the naysayers. Pat

[mikeym1a]

I have always found Larry's post interesting, even the ones I didn't quite understand. I look forward to the results. mikey

[45 2.1]

As to 45 2.1, Byron and now 44man; same old arguments and erroneous assumptions over and over. Instead of arguing simply because my name is on the post or hypothosizing non relevance try conducting the simple test with a 30-06 that I've mentioned numerous times. You will find the RPM Threshold. Larry Gibson

BTDT with quite a few calibers and rifles. Never found that thing you're speaking about because I found what the real causes was. An undersize boolit being booted out of line with the bore due to tolerance stack was the basic cause along with wrong alloy at inappropriate pressure for it.

Just to clear things up, Larry's "cure" for this does work IF you willing to limit performance in several others regions of the cartridge's performance you've chosen to work with..... along with the money for the barrel and fitting for each rifle you want to do it to. Or, you can learn how to "push the envelop" as he puts it and load better ammo. That's your choice to make though.




"I must be missing something.
Larry has attempted to illustrate through multiple posts, for a long time, that this "RPM threshold" is an area where average cast shooters, using average firearms, and employing basic loading procedures are likely to see a deterioration of accuracy as velocities are increased if the standard grease-grooved cast projectile exceeds 140,000 RPM. He has, as far as I'm aware, always maintained that this "threshold" is NOT a limit, and can be exceeded by various means...better casts, better loading techniques, better component choices, better firearms, and better ammo-to-firearm fit.

Then what exactly is the point? Reload better or what. Seems to be the same argument one would make about taking a factory sedan to a drag race......... you already know you're going to lose.


It is pretty disappointing to see an interesting study about to take place by someone who's trying to help us along as a group by perfoming a series of time consuming tests being sniped at.

Larry already posted the results... some years ago now. I'm sure he would be happy to post where or refresh the thread where it could be seen. Ask him to do so.


I read through 10 pages of attacks and disputes with no test results.

This is really old thread.... see the above reply.


There was a time when this site had more than it's fair share of people who were already busting caps and throwing away lead, who just wanted to talk about the way they saw the results.

Yep, that was before the actual Cast Boolits appeared, when it was Shooters. You're relatively new here. Lots of really great old threads in the archives.


A man on another forum ran a test with 4 different 6mm cartridges, but all the barrels were cut from the same chunk of steel.

If a call to bartlein can be made, and they can cut 3 different 30 cal twists into 3 different barrels from the same chunk of steel,

That would cut a lot of variables out to a manageable level. There are a few people here who have seen the reject barrel bin where the barrels are that don't meet the custom barrel makers quality standards. The same chunk of steel would negate that possibility.

[45 2.1]

Goodsteel,I like your post,there's people on here,one in particular who does post unbelieveable groups and performances from rifles but as yet I've never seen a group posted ever,

I've been with the old Shooters and post era sites since '99. In that time I've seen one group, shot by someone else, that beat the CBA records for group size, not shot count. You can go to the CBA site and look up those national records yourself..... everyone here should in fact. You will see groups well below 1/2" listed, shot in competition witnessed by the people shooting. That should open several eyes here as to what is possible with properly put together rifles and loads. None of that has been done here though..... Which means something unbelievable here can be rather normal someplace else.

I attended a CBA match long ago where one of the owners of Lock, Stock and Barrel was attending with his granddaughter. After the match he invited all of use to shoot his rifle, a Miller-Dehaus in 32-40. We breach seated the long tapered boolits and loaded the powder into the case at the bench. Everyone had a 100 yard 3 shot group that had touching or overlapping holes in the group on the target. Good equipment is a wonderful thing.

[GhostHawk]

Larry please don't give up.

I know you are taking some heat over this, and having some problems with the net.
But many of us have been quietly patiently reading this thread and cheering you on.

It finally dawned on me that you were not hearing your cheering dept.

YEAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHH LARRY!

Go man GO!

Scientific method DEMANDS imperical data, provable data, data with as few variables as possible.
Every time someone pushes the edge we learn, even if he fails.

Go LARRY! We are rooting for ya man!

[mrbill2]

I try to keep a open mind but can't help but think about all the people in the world that were convinced the earth was flat and they could prove it too.

[NYBushBro]

Has this test ever been done, and have the results been posted (without wading through 10 pages of 'discussion' - to put it politely)?

Larry: in the future, I would suggest running your tests first, and letting people argue about the findings, rather than the "pre-test" theories. Just my dos centavos...

PS: Thanks for your work with the LeveRevolution powder...

[Love Life]

Has this test ever been done, and have the results been posted (without wading through 10 pages of 'discussion' - to put it politely)?

Larry: in the future, I would suggest running your tests first, and letting people argue about the findings, rather than the "pre-test" theories. Just my dos centavos...

PS: Thanks for your work with the LeveRevolution powder...

That's what I do. Makes life easy.

[btroj]

Tim, show me anywhere in the firearms industry where rpm is a standard unit of measure in place of fps?

I don't buy commercial ammo with a chart showing rpm from specific twists? Why is that?

Larry is right, there is a certain point at which a specific alloy, powder, and bullet design begin to show deterioration in accuracy. No disputing that.

What I want to see is what happens when we change the loading method, alloy, powder, and bullet design. Those are things "Joe Everyman" can easily alter. Most shooters aren't willing to put a new barrel on a rifle but they will buy some super hard or a new mould. Pretty much any caster is willing to try heat treating an alloy.

Why not focus on what it takes to beat this "threshold" rather than view it as a ceiling? The more we discuss the existence of a threshold the more it perpetuates the concept that cast bullets can't be shot at high velocity with any level of accuracy in the rifles most of us own. I don't see that as pushing the envelope but more as maintaining the status quo.

Too many have said they can beat this threshold to make me buy into it as much more than a limit for normal casting and loading techniques. It is beatable so my view is to ignore it and do what it takes to get the velocities I want.

[Love Life]

What I find hilarious I people trying to create uber accurate cast loads with a rifle that is 1-2 MOA with good jacketed loads...

Loading very good, consistent, and uniform ammo is a chore. A big chore. From weighing to primer pockets to turning to reaming blah, blah, blah.

Yes, anybody can ALTER their ammo quality, but without dropping good dollars you favorite set of dies and weighed charge of splody powder will only take you so far.

Screamer groups are nice, but your rifle has to print legit groups consistently.

The rifle itself is a major portion of the equation for wallet groups.

[MBTcustom]

Tim, show me anywhere in the firearms industry where rpm is a standard unit of measure in place of fps?

I don't buy commercial ammo with a chart showing rpm from specific twists? Why is that?

Larry is right, there is a certain point at which a specific alloy, powder, and bullet design begin to show deterioration in accuracy. No disputing that.

What I want to see is what happens when we change the loading method, alloy, powder, and bullet design. Those are things "Joe Everyman" can easily alter. Most shooters aren't willing to put a new barrel on a rifle but they will buy some super hard or a new mould. Pretty much any caster is willing to try heat treating an alloy.

Why not focus on what it takes to beat this "threshold" rather than view it as a ceiling? The more we discuss the existence of a threshold the more it perpetuates the concept that cast bullets can't be shot at high velocity with any level of accuracy in the rifles most of us own. I don't see that as pushing the envelope but more as maintaining the status quo.

Too many have said they can beat this threshold to make me buy into it as much more than a limit for normal casting and loading techniques. It is beatable so my view is to ignore it and do what it takes to get the velocities I want.

First of all, you don't "beat" the RPMTH. That's as ludicrous as saying you're gonna "beat" FPS.
Second, it's not a ceiling, it's a gauge of measure. The only folks saying the RPMTH is a limit is are the ones that have turned this thread into a debate instead of a simple, interesting experiment. At no point has it been said that the RPMTH is a limit. It's simply a place where things change suddenly. You can ignore that to your hearts content, but it's like gravity: if you jump off a cliff, the fall might be long or short, but there is definitely a big red stain waiting for you at your destination.

We are focusing on what it takes to raise the RPMTH, and we are doing that by not considering it to be a ceiling in the first place (seriously, have you even read the sticky? Do you have any idea what we are talking about other than the jaded version you got from someone else?) I mean if I were going to bust someone out and disagree wholeheartedly with something they had written, I would think that a good place to start would be to read what they wrote before launching an assault, so I don't sound like an idiot, but that's just me.
Here it is, in case you havn't found it yet. Pay especially close attention to the first line in the third paragraph:
http://castboolits.gunloads.com/showthread.php?208186-RPM-Threshold-barrel-twist-velocity-chart

If people are saying that they can "beat" the RPMTH, they really haven't read the sticky very well.

[MBTcustom]

As far as RPM a standard of measure in the Firearms industry SAAMI addresses Projectile Rotation, anything that is rotating is measured in Revolutions Per XXX (usuallay a time measure minuate, second or something).
Look at the .220 swift Is it the velocity or the RPMs that blows the 40gr projectile up when you push past the 4000FPS velocity?? IT IS THE FORCES of SPINNING not acclerating though the medium of air. Centrificatcal Forces act upon the lead core to seperate and push against the copper jacket, even though the copper has more elasticlty etc strength the lead specfic gravity of being spun over rides the Coppper jackets intregity. What does that have to do with cast? Well think about that is the level of RPM that increases the imbalance of the lead bullet be that separation of the Bullet itself or elongation of a air cavity . The RPM threshold even plays into Jacketed bullets it's just at a differant location based on the same factors, It's just Jacketed IS WAY more forgiving

Edit to add as a FYI:
Look I'm not in Larry Camp on this, or anyones elses Camp rather my own.

But, I want to see what the man will bring to the table. I have PM'ed Larry Gibson Numberous time since I joined this board NEVER has he PM'ed back EVER. Now he might have never recieved this 10 or so Pm over a period of time asking his thoughts etc etc. BUT from what he is stating about the threshold it makes sense So let him prove it durn it.

Nah nah nah, thow art unfit to read and conclude for thineself. Thou must be assigned a translator to tell thee what Larry truly meaneth when he posteth.

To all those trolling this thread, from up hear on the edge, it sure looks like a nice hole ya got going on there. Just keep shoveling, I think you're making headway.
I really don't know what to tell you. Superstition, trolling, and vague postulations kind of fall flat on their face when confronted with intelligent men who deal with science and fact.
You can't even argue with Larry without misquoting him!
I think the emperor is losing cloths rather quickly all of a sudden.

[MBTcustom]

You know what's really great? We really don't have to argue the point at all. The naysayers are going to end up arguing with their own rifle and trying to convince it what it's doing is wrong.
I'm sure that at some point, somebody is going to come along with a rifle that shoots 2600 with a 12 twist and they shall proclaim with proud indignation that they have "beaten" the RPMTH.
At that point, I have one question that is going to make them go green in the gills: "So what's it do at 2700?".
Then they'll get mad.
They were mad before, they are mad during, and they will be mad about their "success".
Hmmmm, what a frustrating way to look at cast lead.

[35 shooter]

goodsteal, you definitely have a way with words. it really is enviable. It's always in a way that's cuts to the point and really is very hard to argue with. This place is fortunate to have such good mods. That's about all i have to say on this thread. Except it is a shame a fellow can't carry on a simple experiment in relative peace on his own thread sometimes.

[JonB_in_Glencoe]

I probably should just avoid this, but I have a question...to anyone...


snip...
I mean if I were going to bust someone out and disagree wholeheartedly with something they had written, I would think that a good place to start would be to read what they wrote before launching an assault, so I don't sound like an idiot, but that's just me.
Here it is, in case you havn't found it yet. Pay especially close attention to the first line in the third paragraph:
http://castboolits.gunloads.com/showthread.php?208186-RPM-Threshold-barrel-twist-velocity-chart
Tim, thanks for posting this link...I believe the second paragraph is the most eye opening one for me, I quoted it below.

Let us keep in mind the RPM threshold most often falls in the 120,000 to 140,000 RPM range with regular lube groove cast bullets. Exactly where the RPM threshold will be in fps depends on numerous factors; alloy, bullet design, fit, sizing, lube, GC’d and seated square, powder burning rate and the length of the barrel, etc. The RPM threshold may be lower than 120,000 RPM by careless casting and loading techniques or when using very soft alloys with very fast burning powders. Conversely, the RPM threshold can be above 140,000 by careful casting and bullet selection and preparation along with careful accuracy enhancing loading techniques, especially those for cast bullets at high velocity such as using slow burning powders that ignite easily and burn efficiently at lower pressures. The trick is to get the cast bullet to exit the muzzle as balanced as possible with as little deformation to it during accelleration. The more balanced the bullet is and the closer the axis of rotation coincides with the center of mass on exit from the muzzle and during flight the more accurate the bullet will be and thus, the higher the RPM threshold will be.

OK, the question.
Isn't the issue really a "Pressure threshold" as opposed to RPM threshold ?

If the pressure is high enough to slump the alloy enough to deform it, it really don't matter what the RPM is...Once the deformed boolit leaves the muzzle, it won't be stable.

That's why, with faster powders and/or softer alloys you lose accuracy at a lower velocity, because of the high pressure associated with the faster powder OR the lower pressure needed to slump a softer alloy.

Yes, there are all the other factors involved with precision loading procedures with precision tooling. But we are talking theory here and it seems to me that the ghost is the pressure curve effecting the alloy and not RPM.

I hope I didn't just fall into a half full septic tank by posting this, But for whatever reason, I felt it necessary to ask this question...As I am other one who is at the beginning of a quest, to attempt to get J-word accuracy with my castboolits at J-word velocities, in a 'off the shelf' rifle
:dung_hits_fan:

[MBTcustom]

I probably should just avoid this, but I have a question...to anyone...


Tim, thanks for posting this link...I believe the second paragraph is the most eye opening one for me, I quoted it below.


OK, the question.
Isn't the issue really a "Pressure threshold" as opposed to RPM threshold ?

If the pressure is high enough to slump the alloy enough to deform it, it really don't matter what the RPM is...Once the deformed boolit leaves the muzzle, it won't be stable.

That's why, with faster powders and/or softer alloys you lose accuracy at a lower velocity, because of the high pressure associated with the faster powder OR the lower pressure needed to slump a softer alloy.

Yes, there are all the other factors involved with precision loading procedures with precision tooling. But we are talking theory here and it seems to me that the ghost is the pressure curve effecting the alloy and not RPM.

I hope I didn't just fall into a half full septic tank by posting this, But for whatever reason, I felt it necessary to ask this question...As I am other one who is at the beginning of a quest, to attempt to get J-word accuracy with my castboolits at J-word velocities, in a 'off the shelf' rifle
:dung_hits_fan:


I personally don't think slump has anything to do with it. I think the faster powders launch the boolit into the rifling too fast to get a good engrave which imbalances the boolit. Slower powders give a gentler push before they kick it in the pants which is enough to get the boolit engraved.
Not only that, but remember that Larry has all of these rifles/barrels hooked up to an Ohler shooting lab, and pressure is something that he can speak definitively on (unless somebody has a problem with that system of measurement also :roll:)
If the issue was tied to pressure, Larry is better set up than anyone on this board to speak definitively on that issue, and he has started this thread on RPM and twist rates instead. Seeing as how he has gone to such lengths to create a test that deals with RPM/twist rates, and seeing as how he owns more equipment and rifles dedicated to the study of these specific parameters I would really like to hear what his take on it is. I still do not know what the outcome of these tests were, and I think this thread has experienced more epic thread drift and trolling, over a longer period of time, than any I have ever seen (seriously, this has got to be some sort of record) and I want to see what the results were.
We can ask Larry what his thoughts are on pressure at launch etc etc etc, but that's a topic for another thread.
This thread is about twist, RPM, and all those other controversial subjects, and it's about to reach sweet fruition.
The side shows have been witnessed, after 6 years the spotlight has swept back to center stage, and I'm ready to hear the fat lady sing.

(edit to add) Of course if the boolit were too get slumped, the RPM is the force that acts on that condition to cause inaccuracy, but if that were the case, then PP would behave similarly, and we know that it pushes the RPMTH up pretty far past what the same boolit is capable of without the protection of the paper jacket, so there must be something more inherent going on.

[Larry Gibson]

Looks like the connection is fixed so I can post again from my PC. Appreciate whoever fixed the problem.

To all who are actually interested in my test results;

If you read through this thread you notice a couple things. First there is a lot of the charts, diagrams, photos and pictures missing. This is an old thread and with the several updates to this site they obviously were deleted via the updates. Also there is a lot of extraneous discussions and questions not related to the tests and what we seek to find out. Sgt.mike and Goodsteel's recent recapitalization of the intent of this thread is the direction I wish to proceed.

As it has been some time since I last posted test information in this thread I must compile the test results later conducted. Yes I have conducted numerous tests since many of you may find interesting. I certainly found the results interesting. Those test results have pushed me further to success with shooting cast bullets (your basic commonly available designs cast of ternary alloys) which are lubed and GC'd as commonly done. It has been an interesting path with trials and tribulations. I have learned a lot about cast bullets at high velocity since this test began and there is more to learn.

Unfortunately this thread is too long and strays to far and too much. The RPM threshold is real and it is not a "limit". In the test results to be posted we will see how it can be pushed up. However, the main thrust of my testing became focused not on proving the existence of the RPM threshold as that has been proven to most but to see just how fast a regular cast bullet could be pushed and maintain reasonable accuracy to at least 300 yards. To me "reasonable accuracy" means sub 2 moa or less to 300 yards with linear dispersion of the group size as the range increases. Let us understand that 'reasonable accuracy" does not mean the "best accuracy" the rifle is capable of. I have subsequently conducted tests with the 10, 12 and 14" twist test .308W rifles to find an answer (that is "an answer"....perhaps not the only answer) to that. Obviously the 14" twist offered the highest velocity potential while maintaining that accuracy level. Thus some very good success has been obtained with the 14" twist rifle at 2600+ fps.

Thus I will post a couple groups here showing the success and then will be finished with this thread. I will start a new thread with additional test results and perhaps some of the older missing data to show the progress. Let us keep the discussion to the point and not off on esoteric topic please.

Below is a 10 shot 100 yard group and I will admit it is one of the better groups. The 14" twist Palma rifle normally holds around 1.5 moa for 10 shots out to 300 yards. The next photo is of 100, 200 and 300 yard groups shot consecutively. There was a 9 o'clock wind and I did not hold for it so we see the wind drift as the range increases. Next is a photo of the rifle.

The rifle is a M98 byf action pillar bedded into a proto-type fiber glass/kevlar stock I salvaged from the makers trash can. The barrel is a take off Schultz & Larson 27 1/2" Palma barrel I fitted to the action and chambered with a .308W match chambered to minimum specs. BTW; the 10" twist rifle is also chambered with the same reamer and both it and the Palma rifles headspace is the same minimum as in the 12" twist M70 .308W target rifle. The scope on the Palma rifle is a Weaver T-16.

The bullet used is the 311466 cast of #2 alloy and WQ'd. The bullets are visually inspected/sorted for defects and then weight sorted to .1 +/- gr. The selected bullets have the Hornady GCs seated on a Lyman 450 and are lubed with 2500+ in a .311 H&I die. The cases are well fire formed and match prepped Winchester .308W Palma cases. Primers are WLRs. The powder is AA4350 at 100% load density with a charge of 48 gr weighed. The 311466s are seated so the top of the GC is in the case neck and the front drive band is against the leade.

See those of you interested in learning on the next thread, thanks for the interest and the support.

Larry Gibson

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