Barrel twist for close shots

[fourfive8]

Yes........ At least to a point. In calibers .458 + a properly designed flat nose solid with a meplat at least 65% of caliber will self stabilize during terminal penetration to 90%-95% of its total depth of penetration with no engraving at all. I had two rifles that were supposed to be .474 and both barrels were oversized to .478, some bullets had no engraving at all, some were just barely marked. Bullets tested that had 65% meplat of caliber penetrated dead straight to at least 90% of total penetration. I also had one oversized barrel in the field for buffalo in Australia, I did not realize it at the time, shooting CEB Raptors and Solids I experienced straight line penetration to all depths reached in buffalo. It was only when one Raptor base was recovered that we discovered zero engraving on the bullet, it was an oversized barrel from PacNor at 1;10 twist rate. Which twist rate made no difference in this case.

Meplat Size and Nose Profile are #1 and #2 of the 8 factors of terminal penetration of solids.

Twist Rates I rank at #7 of the Factors related to Solid Terminal Penetration. Twist rate becomes extremely important and assists in deeper straight line penetration when using solids with less than desirable meplat size. With the faster twist rate you will increase the depth of straight line penetration with these solids or FMJ. Solid design trumps Twist Rate however in straight line penetration.

Question about results of an undersized bullet not showing land engraving but recovered after passing through variable dense tissue on a straight line path (suggesting point forward travel with stability).... If a conventional bullet is not stabilized either aerodynamically/hydrodynamicall or gyroscopically or in some combination of both as it flies through the air, how does it magically become stabilized as it impacts and passes though a much more dense and variable media like a big game animal? My understanding of the physics involved indicates a flat meplat does not provide external stabilization to a monolithic, non-deforming bullet as it travels through any media, including a dense or aqueous media, it simply creates an environment through which an otherwise stable bullet can fly farther with continued stability through that media.

A non-deforming, bullet must behave according to the laws of physics to have stable flight in air or any media. A few bullet designs, like the hollow base Minie', use two forms of stability... minimal gyroscopic spin stability along with the aerodynamic/hydrodynamic stability where the bullet's center of gravity is forward of the center of pressure. Some deforming bullets will transition to a partial hydrodynamic stability as the bullet enters and passes through a more dense, aqueous media where the front expands. This stability is most noted if the front part of the bullet is lead core and the rear is less dense, solid shank.... creating a weight forward condition (center of gravity is forward of center of pressure) for stability.

Seems like no matter the bullet design or shape , if it is not flying point forward and is stable through the air, the chances are pretty good it will impact with some yaw and if severe, practically sideways. Witness that on paper targets showing unstable bullet impacts .

 

[michael458]

Concerning Solid Terminal Penetration only............

When a Solid begins its terminal penetration, and the medium is aqueous, and in animal tissue which is also aqueous, think of it as a "Front End Drive"............... The Meplat Size and Nose Profile drives the bullet path. All solid tests here took place from 25-50 yards. Some tests were conducted closer at 10 yards, but only a smaller percentage. The vast majority was 25 yards.

In tests for meplat size stability occurred in all cases at 65% Meplat of Caliber. Meaning that the terminal stability gave straight line penetration for the entire depth of penetration, considering that other factors were correct as well. Nose Profiles made a difference, Construction and Material, Nose Projection above the top bearing surface, and radius edges are also factors of design. When you drop below that 65% Meplat of Caliber then the straight line penetration began to deteriorate, and you could see velocity and twist rates become a factor at that point. Dropping to 50% Meplat of Caliber was no more stable than any round nose FMJ or Solid. You would have bullets turn off course, tumble, and even leave the medium.

I very rarely, if ever did much shooting of my big bores beyond 50 yards. In all my hunting experiences I never seen the point, taking shots on dangerous game beyond 50 yards was extremely rare, and many many times much closer than that. Even my over sized barrels would still shoot 3 rounds in a hole at 50 yards, and I had 3 such guns that were tested, and one made it to the field.

I had two of the Big Five Winchester M70 Rifles in 470 Capstick. Somewhere along the way, when Winchester Custom Shop received the barrels, they were not .474 but slugged at .478 caliber. There were only 125 of these guns, and I was probably the only one that was actually shooting them, or trying to anyway, there were other problems with those beyond the over sized barrel.

Here in this example we tested a 500 Hornady DGS.... 57% Meplat of Caliber.........

In the same rifle the 500 Barnes was also tested. The Barnes had a 67% Meplat of Caliber
and it is very clear that while it was not 100% Stable, the straight line penetration with the 67% Meplat of Caliber it was able to penetrate in a straight line nearly double the depth of the lesser Meplat of Caliber bullet.

My good friend and test associate brought one of his 470 NE rifles in to test, and we were also working at the time with the new design BBW #13. We assume the barrel was a proper .474, but that is not 100% confirmed at the time. You will see that the Smaller Meplat of Caliber bullet did better at the assumed .474, but not by much, and it still lost stability. And, the proper design larger meplat size did not loose stability at all.

The Cutting Edge Solid meplat of caliber was sized down to 67% later, this allowed 100% feed and function in proper designed bolt guns, otherwise known as a Winchester M70 Control Feed. We went with a 450 gr version for my own 475 B&M and a 350 gr version for the lesser capacity Super Short.

The B&M rifles had 1:10 Twist PacNor barrels..... with the exception of the one that was taken to Australia, we later found it too was oversized, but that rifle was not used in any of the Bullet Tests.

In 2014 my Son Mark David used his 475 Super Short to take a medium size elephant with the 350 #13. It was a side brain shot at 10 steps, it was one and down, and the little 350 .474 caliber exited the far side. I was backup on that one, with a 500 B&M, but damn I didn't even get to fire a shot......

 

[Velo Dog]

The projectiles used out of them ( Abrams tanks ) also have stabilizing fins.

We have so much hi speed film of bullets. I have never seen anything that would indicate that was going on. If it were on film it would be all over the place. Again this is with a bullet that is stabilized or over stabilized. Understablized bullet one of the three conditions will happen. You would also see it in paper targets, bullet holes would not be perfectly round. You will find the oblong, that is with an understablized bullet barrel combination. Not over stabilized, like what the author was claiming.

Hello again Inline6,

Again I apologize for getting my tank makers, models and vintages confused.
Indeed the main gun in the USA Abrams Tanks is smooth bore and so obviously I was wrong about whichever make / model of tank was shown firing, in the video I had watched some years back.
Below are some snippets that I recently found, showing the tilted tank projectile thing I was trying to describe.
(I hesitate to guess which make and model of tank this one is).

Best Regards,
Velo Dog.