I was absent from here for about 6 months while I was off doing MANY of my unscientific tests. I felt that I could NOT be distracted by this board which so often happens with others of varying opinions. So .... fortunately and unfortunately for many here, here is one of my tests.
The test began involving 4" and 6.5" 44 S&Ws for hardness requirements, both with throats smaller than bore diameter (that is another thread all to itself) and penetration.
From this testing, I got another wild idea to try. And that is the subject here. RPMS can not be measured. BUT!!! RPMS are not necessary in a vacuum. Only when traveling through some medium, such as air ............... OR animal flesh. Thus, the depth of "accurate" penetration could be thought of as a reflection of "actual RPMS" and only "IF" deformation could be controlled. So how could I see this?
The idea was to use increased resistance to slow penetration without causing ANY deformation. That leaves RPMs as the sole factor for stable, penetration depth. This is too hard to do at high velocity, so lets slow it down and soften the slugs. I used a 30 caliber rifle for this so that it would make it easier for others to understand and correlate it to as we went along.
I mixed up some ballistic gelatin provided by a friend in long plastic (double bread) bags so that I could see inside. I used one milk jug with water in front of the gelatin for each shot to slow the projectile uniformly with the intent to stop it in the gelatin tubes. It took a lot of working out the kinks, but what I eventually did, I used Linotype for the nose portion of a pure lead body bullet utilizing my 160gr, GC, 30 caliber bullet design with a 60% meplat. This was to prevent mushrooming from contaminating the results. All of this was fired from my 30-06 at 50 yards which is unimportant, except it establishes a base line.
Accuracy levels were no real consideration here either. I say that with the understanding other than what the "best" accuracy level was and at what velocity level that occurred. I was using 4759 powder, magnum primers, and Dacron to maintain shot to shot velocity consistency with a chronograph in front of the impact area. What happened during this testing was an epiphonony on RPMs.
Accuracy peaked between 1150 and 1200 fps. It began to deteriorate rapidly above this level where I shot it up to 1600 fps. 1600 fps was the stopping point because accuracy was about 2 1/2" which was the limit for a guaranteed hit in my gelatin tubes. And the nose also began to exhibit signs of deformation which would contaminate these results.
What happened was amazing and a truly key point!!!. Penetration peaked, when accuracy peaked. Now why?
As velocity increased from the 1200 fps level, more violent reaction was noted in the water action at the jug resulting from the increased velocity level strike, but penetration was no deeper at 1500 fps than it was at 1200 fps. And at 1600 fps, penetration actually declined. No mushrooming was present. So was RPMs actually declining as velocity increased?
At 1400 fps, the penetration was clearly no longer straight line. The slug began to veer off coarse and became RPMy looking as it traveled. At 1600 fps, the penetration was truly erratic and the slug even began to exit the side of the gelatin tube on a few of the shots.
Next I hardened the slug. This time I used Linotype, just to ensure that there was enough of a difference in hardness to prove my theory. The Linotype bullets at 1600 fps were vastly more accurate when shot at the target. That's not news, but they mysteriously began traveling on a straight path again through the ballistic gelatin. Some even began to exit the back of the tube which was another 4.5" of bullet travel over the soft bullet with the hard nose, peak penetration.
Why? Deformation was zero. Velocity was the same adjusted by load and chronograph. In fact, the lino bullet was 6.2 grains lighter than the pure lead slug used at the beginning of these tests. So, from a reality standpoint, the Linotype slug should have penetrated less material, not more. The answer? Increased RPMs baby! Increased?
When accuracy peeks, (at the first accuracy point) RPMs peak. RPMs remain the same for a short velocity increase and then eventually they begin to decline as velocity continues to increase. The guess is that the bullet fails farther and farther back on the design to induce rotation upon exit also resulting in a poor accuracy reducing result. But I don't have to be right in my guess, only dispel theory or wives's tales. I suppose that if pushed hard enough, or with low enough rifling, that RPMs could theoretically go to ZERO. This makes the discussion of RPMs a low effect phenomenon, not a HIGH one. And this turns the discussion to a lead strength issue and the ability of the gun to impart rotation issue during a controlled launch.
So what does this explain or dispel that we deal with everyday on the board?
Well this supports the old timers belief that the longest barrels were best for lead. And I suppose that this is because a fully accelerated bullet is experiencing no rotational acceleration at muzzle exit. So, in effect, it has higher RPMs because it is in effect stronger as it leaves the bore. It also explains the use of slower twist rates adding to bullet strength or launch capability. As it turns out, the slower twist rate barrel can be launching at the higher RPMs when compared to a faster twist rate barrel at the same velocity. Particularly in barrels that are too short in relation to case capacity to bore diameter to achieve enough acceleration before exit. It also supports low muzzle pressure upon exit and the use of faster powders for lead which can be said to be sort of the same thing.
It explains worn rifling height issues with older / worn barrels. It explains why different people can shoot the same load at the same velocity inside what is commonly thought of to be the cast bullet (RPM) zone and still get different accuracy results. It explains the failure of PB designs at around certain velocity (RPM ) levels. It also supports old timers bullet design beliefs of wider base bands on their PB designs. There is much more here, but I have already lost many folks who will need to read this again and digest it accordingly if they truly ever can. Cause it is cast boolit heresy.
What does these tests dispel? Well it dispels the high RPM theory for causing wild trajectories beyond a certain point. Accuracy loss occurs ONLY because enough forward velocity is lost that stable flight is no longer possible from a " TOO LOW " RPM condition at the ballistic coefficient / wind resistance level it is traveling. It also dispels the matching bullet to twist rate theory, as a heavier bullet that goes slower than a lighter one, has more surface contact with the rifling to which to impart and maintain rotation / RPMs during acceleration .... at an equal bullet hardness. It helps to explains short barrel finickiness compared to longer barrels, especially in handguns.
This unscientific testing (:grin) essentially turns the cast world upside down on many accepted issues. And while I freely admit that it doesn't explain everything, it doesn't have to. Only to force people with other theories to look to another coarse. It can serve as an example to the futility of scientific testing that results in a false conclusion. No matter how good or scientific a test really is. At least it can alter methods for those who will continue the search for truth which doesn't exist.
There it is in a description of how it was conducted so that it can be repeated. Anyone care to offer an opinion on my methods or conclusion? Ahhhhhh please, somebody!
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Originally Posted by Bass Ackward
