Barrel twist for close shots

[Inline6]

You believe the solids were being destroyed at close range?

He talked about a 375 that hit the jaw bone of a buffalo at an angle. If it is from the picture in his book it was a round nose. They are not know for straight line penetration. I think that was one of those things that does not happen often. If a bullet deflects it is not going to stay straight physically.

 

[Inline6]

The other "solids" not mono he explained it was bullet failure due to others things. Meaning the bullets were crap.

 

[mark-hunter]

I do not know if hunting rifle bullets do this or not.

I think that Abrams tank has smooth barrel.
So cannot be compared to rifle bullet ballistic.

Next is rifle bullet stabilization (in air).
When cartridge is seated in the chamber it is not perfectly aligned with barrel, as there are tolerances between cartridge and chamber as defined by SAAMI or CIP standard.

So, when fired, bullet is not perfectly aligned with barrel axis.
When bullet is exiting the barrel, axis of the spinning bullet and axis of barrel are still diverging.
Bullet has the spin and will stabilize with gyroscopic effect after certain time, end eventually will come to intended flight path.

(FYI: ships gyro compass after starting takes few hours to stabilize)

So, consequently to the industry tolerances and bullet shape imperfections, there is so called precession of bullet (rotation around the center of mass) and there is so called nutation, a circular movement around bullet tip.

Both phenomena decrease (reduce) with the distance travelled from the barrel.
Longer the distance, less of those two effects. (this means the bullet stabilize with distance)

This is the reason why high end match barrels and custom ammunition have generally smaller tolerances, ammunition for them is custom made (reloaded), all this in order to improve intrinsic accuracy, but the drawback is that not all factory standard ammunition can fit the chamber.

Next is terminal ballistic.
I dont think that there is any correlation between external and terminal ballistic, or stability of bullet in flight with penetration or tumbling, or stability in body tissue. This can be seen in various gelatin tests, or shooting in the water.

Some bullets penetrate better, some are tumbling. Meplats and round nose solids are known to be most stable penetrators.

Bullet factories test their products till they get what they want to get, in terms of terminal ballistic.
There is a lot of trial and error in entire process of testing when designing a bullet.
But general accumulated knowledge with these tests historically has increased significantly, so they pretty much have an idea in advance how new design will perform.

There is only one case that I remember reading somewhere is that same bullets', of expanding type, will have better terminal effect on animal - with faster twist.
I think this is because they cut the permanent wound channel with faster rate, and thus in theory could cause more bleeding on animal - with more rotations within penetration path.
(If CNS is not hit, then bleeding is primary cause of death in animal shot).

Scheme from internet (distance increase to the left):

 

[Inline6]

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.

 

[fourfive8]

Bullets are subject to tremendous kinetic forces when they hit things. There is a velocity squared relationship. Even, solids will do all kinds of odd things when hitting or passing through media. And as has been posted, all solids are not created equal. In the kinetic energy equation there is a reason it is- 1/2 m v squared. The 1/2 part and the squared parts are both key to understanding the concept. Of course there may also be much truth in what Robertson has reported. But a cause-effect conclusion is a little more difficult. Obviously a bullet that hits something while it's point is yawing around in precession, will have little chance of correcting the instability as it encounters something more dense than air. So, IMO, the symptoms of less than expected penetration, as being discussed here, could be caused by either or both of the most probable possibilities. Either the bullet's integrity/form has compromised because of the higher impact velocity at closer range and/or it is not fully stable in flight at the time of impact. I think the former is more commonly the culprit but that's not 100% either for all cases.

 

[shootist~]

Greetings C.W. Richter,

I agree with you that it’s sort of comical when a neophyte tries to argue against an expert.
It’s like a toddler saying they want candy for supper because it’s healthier than salmon.

That said and at the risk of sounding like I’m demanding candy for supper ………Dr. Robertson once was recommending persons using bolt action rifles for hunting, should upon firing each shot, lower the rifle from their shoulder, to somewhere near belly level, while running the bolt to reload their chamber with a fresh live round.
And then, bring the rifle back up, press the butt back into their shoulder, regain their sight picture and repeat when practicing and / or when necessary.

I do not recall why he recommended this but it might have been so the hunter could better see the critter they had just shot ?
Or perhaps visually watch the next round as it is being chambered ?
Not sure anymore what he said his reasoning was on this.

Dr. Robertson is rightfully a living legend and a tower of wisdom for sure.
I am the proverbial stupid stump, compared to him.
However, I learned to operate bolt action rifles from the shoulder, still pointed at my target as each round is fired, the spent brass ejected and each new live round chambered.
Live target or otherwise, my rifle remains firmly in firing position hard against my shoulder, “Sergeant York style”, as I operate the bolt each time.
My father taught me this method, beginning at age 16 and I will continue with it, because it has worked well for me plus, it honors the old man who wasn’t perfect, (he fancied tennis and golf ….. disgusting), but he saw too it that I learned how to stay safe and shoot straight.

blah blah whatever,
Velo Dog out.

The short Youtube video below is probably what you are referring to. I stumbled on it awhile back and happened to save it.

Paraphrasing, from the video, it's to deal with the high number of short-strokes they see from [mostly European] clients unfamiliar with magnum length actions. Also aids in keeping track of which animal you are following.

Dr Robertson's comments near the end on the "loudest sound in Africa" is priceless.

 

[mdwest]

It’s like a toddler saying they want candy for supper because it’s healthier than salmon.

Wait!

Are you saying it’s not?!?!?!?!

 

[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.

Hi Inline6,

Thank you for the correction.

The video I watched was quite some years ago, on television.
It was a documentary about tanks, from various countries.

And I think you’re right about the Abrams main gun being smooth bore.
One of my kin was a Tanker in an Abrams.
Now that you mention the smooth bore, it sort of rings a bell that he told me the same thing.

Also, I do not recall the projectile in said video having any fins on it.
In fact it seems to me the projectile was spinning, as if having been fired through a rifled barrel.
So, that leaves me believing it was fired from some other tank, not the Abrams.

Nonetheless, whatever design of tank it was fired from, the projectile flew for a ways at first, slightly nose down.
It wasn’t until it was down range a bit that it stabilized and travelled in a more lateral attitude.

I am not a super technical person but, this topic is quite interesting for me anyway.
Thanks for sharing.

Cheers,
Velo Dog.

 

[Velo Dog]

The short Youtube video below is probably what you are referring to. I stumbled on it awhile back and happened to save it.

Paraphrasing, from the video, it's to deal with the high number of short-strokes they see from [mostly European] clients unfamiliar with magnum length actions. Also aids in keeping track of which animal you are following.

Dr Robertson's comments near the end on the "loudest sound in Africa" is priceless.

Yes, that is the very one.
Thank you for posting it.
And, with Dr. Robertson plus other PHs, noticing a pattern of clients short stroking their bolt action rifles, I can understand why they have developed the method shown in their video.
Now watch, next time I go to the rifle range, and resume my old familiar from-the-shoulder rifle manipulation, I will start short stroking my .375 for sure.

 

[C.W. Richter]

You believe the solids were being destroyed at close range?

early on in the 'cast, he talks about really old FMJ bullets (not solids) breaking into their respective pieces-cup/core/cap. I've never broken a Barnes banded brass solid!

 

[C.W. Richter]

Agreed on points like that. An old-timer 25 yrs my senior used to take me out hunting as a kid and had some really strange habits he tried to press upon me (ziploc bags in boots-sweat/freeze!) and similar pointing muzzle down at times...If you're actively firing, cycle the damn thing, stay on-target and fire! lol As a lot of the old radio DJs were fond of saying (while broadcasting, writing a book or article-NO dead air) just keep it going talking about whatever....LOL

'No loss of love for his contributions to our passion, but if you want to read or see some strange mannerisms, subscribe to the Capstick school of safari prep! LOL His choices were odd, but his choices. Him, a writer weaving colorful stories and extending the yarn as much as possible for profit. Robertson, a true technician. I'd say 99.9% of what's said, ballistically, is right on target. He also gives credit to some of the "newer" monometal bullets, and not just Barnes. A Zim PH was going to take me to meet KR, but time didn't permit (he was also adamant that I buy Courtney shoes on that same trip we didn't make.) LOL I looked at 'em like they were made of retreads that fell off a truck and landed on the shoulder of the road, and stitched by inuits...I'll keep the Kenetreks (most comfortable, EVER, and less objectionable staring at your feet back home while they continue to serve you.)

 

[C.W. Richter]

Yes, that is the very one.
Thank you for posting it.
And, with Dr. Robertson plus other PHs, noticing a pattern of clients short stroking their bolt action rifles, I can understand why they have developed the method shown in their video.
Now watch, next time I go to the rifle range, and resume my old familiar from-the-shoulder rifle manipulation, I will start short stroking my .375 for sure.

it makes sense. i did it once in an M70 and my Son backed me up with a fantastic follow-up. it was a not so subtle reminder to simply always pull the bolt ALL the way back or at least know that it (CRF) picked up the cartridge. some will even jam the cartridge in the magazine if short-stroked and slammed forward. (recalling the short-stroke, i believe it was caused by my stuck-wide-open lower jaw pressing against the rifle!!!!! lol)

 

[fourfive8]

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.

Yah I think the 120 mm Abrams tank penetrator round fired out of a smoothbore could best be described as a sabot'd dart. The closest thing I have experience with is a hollow base Minie' which is partially stabilized like a dart or most similarly a badminton shuttlecock. A Minie' has a very slow rate of spin out of most original bores. The result of my penetration testing of the pure lead MInie' into the same media I use for all high power testing was an eyeopener! I remember a slow spin rate 69 cal pure lead Minie' straight line penetrating farther than many of the other premium high power expanding bullets in the 270 to 338 cal class I have tested. I do not know if this correlates conversely with anything related to penetration (or lack thereof) of bullets with very high spin rates or not. ??

I have also heard, but am not sure about the validity of, the theory that a very high spin rate at impact can increase the loss of a bullet's structural integrity because of the increase in centrifugal/centripetal force (angular momentum) at the higher spin rate. ??? Plausible but would require a lot of detailed testing to confirm.

 

[Inline6]

Yah I think the 120 mm Abrams tank penetrator round fired out of a smoothbore could best be described as a sabot'd dart. The closest thing I have experience with is a hollow base Minie' which is partially stabilized like a dart or most similarly a badminton shuttlecock. A Minie' has a very slow rate of spin out of most original bores. The result of my penetration testing of the pure lead MInie' into the same media I use for all high power testing was an eyeopener! I remember a slow spin rate 69 cal pure lead Minie' straight line penetrating farther than many of the other premium high power expanding bullets in the 270 to 338 cal class I have tested. I do not know if this correlates conversely with anything related to penetration (or lack thereof) of bullets with very high spin rates or not. ??

I have also heard, but am not sure about the validity of, the theory that a very high spin rate at impact can increase the loss of a bullet's structural integrity because of the increase in centrifugal/centripetal force (angular momentum) at the higher spin rate. ??? Plausible but would require a lot of detailed testing to confirm.

I'm not sure, it is hard to say. One thing I do know, the faster the bullet the quicker it bleeds speed. (In air aways, I would think that holds true in everything). Not sure if the slower speed along with the shape of the bullet is why your test worked as well as it did.

You know the math and the reasons the math works. I'm just a guy that squeezes a trigger and tries to hit targets.

 

[Velo Dog]

Yah I think the 120 mm Abrams tank penetrator round fired out of a smoothbore could best be described as a sabot'd dart.

Greetings fourfive8,

I agree with you.

Seems like the US Military even refers to the “dart” round, for their 120 MM Abrams main gun that you describe, as the Sabot (“say-boh”) Round.

However, as has been rightfully pointed out earlier in this thread, my 70 year old memory is not supremely accurate these days, (if it ever was).

So, I could be wrong again.

Cheers,
Velo Dog.

 

[Wyatt Smith]

@michael458 please correct me if I’m wrong, but I recall you saying a properly designed solid will stabilize in a medium with no rifling whatsoever?

 

[NDWoods]

I have had someone tell me on a long range course that some bullets are stabilized better at 200 yds than 100yds.
I have shot A LOT of rifle ammo and I have yet to prove that to be true.
I cannot imagine a bullet being unstable at 30 yds that would otherwise be good at 50yds or 100yds, but my imagination is not science.
The stability theory should be able to be proven with radar, gel, or some other sort of measured means.

 

[TMac]

I have had someone tell me on a long range course that some bullets are stabilized better at 200 yds than 100yds.
I have shot A LOT of rifle ammo and I have yet to prove that to be true.
I cannot imagine a bullet being unstable at 30 yds that would otherwise be good at 50yds or 100yds, but my imagination is not science.
The stability theory should be able to be proven with radar, gel, or some other sort of measured means.

Some bench rest shooters call it the bullet going to sleep. I have seen it once, I think. My rifle shot OK, not great at 100, just under 2”, but at 200 it held the same group size. 2” at 200 I’ll take, to 300+ things opened up per usual. Go figure.

 

[Tanks]

I have shot several elephants inside of 30 meters and never had an issue with .500 caliber and solids (mono or regular).

Maybe high velocity rat caliber rifles might have an issue.

 

[michael458]

@michael458 please correct me if I’m wrong, but I recall you saying a properly designed solid will stabilize in a medium with no rifling whatsoever?

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.