I'm just an old country boy originally from Pennsylvania and I have an understanding of how you need to vary the rate of twist to handle different length (weight) of bullets for each caliber but I'm a little shaky on other effects at the target end. For a second lets not talk about revolutions per minute or even seconds, but look at the flight to a buffalo standing 50 yards away.
If the rate of twist is 1:12 the bullet rotates completely around its axis 150 times before it strikes and if the twist is 1:16 it will rotate 113 (more or less) times around its axis before it strikes. Since we are talking about buffalo lets say we have a muzzle velocity of 2500 fps. Common sense (theres an oxyomoron for you Ray) would tll me that the one spinning faster (from a 1:12 barrel) would have a "tendenacy" to skid off course faster than the one with the 1:16 twist. Am I right? Do other factors such as location and angle of impact have a bigger effect than rate of twist? Is it testable?

Here's an experiment to try! Do a penetration test where the boards are all slanted instead of perpendicular..do it several times with the boards all slanted in one direction the first time and then try it with the boards slanted in a mixure of ways the 2nd time (but still straight vertically) and then replicate both of these where the boards aren't straight vertically either.

Anyone care to make a predicition?

DB Bill,
If the two bullets are identical, and the ballistics are the same except for the twist, the bullet spinning faster will penetrate straighter. The higher rate of spin will make it more difficult to deflect from the line of flight as the gyroscopic force stabilising the bullet around it's axis is higher.

On the boards, bullet shape plays a much bigger role than rate of twist. On angled boards (all one way) all bullets will turn. A round nose turns most, a truncated cone turns less and a cylinder turns least. With one or two exceptions, expanding bullets are unpredictable as there are too many variables. Angling one left and one right etc. has no deflection effect.

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Gerard Schultz
GS Custom Bullets

Gerald...what is that on the end of the barrels of the young people shooting blesbok? I see they are wearing ear protection so I assume it isn't a silencer. Or is it? Your site looks very interesting and will need to go over it carefully tonight.

I am firmly convinced that the slower the twist the less chance of a conventional bullet comming apart...I believe that rotational spin is what causes bullet failure more than any thing else...I have recently read some interresting articles on this in several African magazines and have about proven it to myself by testing heavy long bullets in a slow twist 375 H&H...I do know that it will not tear the petals off a monlithic such as the fast twisted 375 and I have proved this to myself...I get perfect expansion with BarnesX and GS with the slow twist and with a very fast twist barrel that I used the petals came off in the tough stuff. I'm not sure its critical with a monolithic bullet as thoes petals do a lot of damage and the remainder is a good old solid....go figure.

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

Gentlemen:\Andy tilllman is starting some test on the 23 rd of this month to try to determen the difference that twist rates have on penetration. I think he will be trying 458 with different twist. I for one, think this will be very interesting
George

Hurrah! Someone (Andy) is finally going to do the test. I would agree with Gerard's statements. Maybe Ray is right too. They are not mutually exclusive thoughts. I think George Hoffman and Ross Seyfried both suggest that a little extra twist helps penetration. Makes sense to me. Master Saeed should do some tests too, he does every other project imaginable. I think there is a scarcity of information on this subject, so any testing in this mode would add immensely to our understanding of terminal ballistics.

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Good huntin' and shootin',
RAB

Ray is right (as usual) about twist rate being harder on bullets the tighter it is. We have seen this with testing done with 220 Swifts and jacketed bullets. 40 to 45 grain bullets blow up in flight at higher speeds from a one in 14 twist barrel than from a one in twelve. One can actually see the bullet blow when standing off to the side. It literally disappears in a streak of smoke a couple of metres ahead of the muzzle.

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Gerard Schultz
GS Custom Bullets

[QUOTE]Originally posted by R. A. Berry:

R.A.Berry,
Just curious if you looked at the results of the tests posted on my sight for bullet stabilization and penetration. The pictures are up although they seemed to have disapeared for a short period. The tests where from point blank out to 50 yards with the impact velocity at 2400 fps. I'm not at home right now so I can't remember the difference in muzzle velocity to have the impact velocity of 2400 fps, but it's in the text. The only difference would be rotational velocity. 470 Mbogo
www.470mbogo.com "Comparing the Big Bores"

DB Bill,
They are my twin daughters and it is indeed a silencer. In Africa we do not suffer cold easily and the earmuffs are for keeping the ears warm. We made the suppressors ourselves as a viability study for possible production and they work very well especially for culling work. The market size for centrefire suppressors did not justify setting up production so we only put the .22 rimfire one into production.

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Gerard Schultz
GS Custom Bullets

DB Bill:

Your question is a bit strange. Shooting a Buffalo at 50 yards? Does anyone care what the bullet does?

As usual almost all of the parameters are missing leaving the ballistian to " fill in the blanks ". What is the ogive shape? What is the jacket thickness? What is the lead tin, antimony ratio? What is the angle of the boards?

Are we to presume that you intend to shoot through a barn door? To slaughter a buffalo tied in a stall.

The bullet will leave the muzzle in a rotational configuration. It will be yawing and it won't be rotating around its center. If you want to see what it looks like then take a shadowgram. Pedals won't rip off if there are no pedals.

Cover your eyes - we are going to blow some more smoke!!!!!!

Texas Trollop

I don't feel the variance in penetration will
prove to be either measurable or of any practical import in regard to penetration depth at normal "dangerous game" distance.
I regard to the Barnes "X" it is my feeling that if heavy bones are squarely hit there exists the possibility of "losing" petals, regardless of the rate of barrel twist.
I have yet to lose a petal on a Barnes "X" where only minor bones, ribs and tissue were impacted. On occasion, a petal will roll inwards upon a glancing blow to a large bone but will not break off.
On cape buffalo, for example, one is likely to lose petals on a square side shoulder hit, especially if the bullet carries on through to the opposing leg bone.
I have lost all 4 petals on this shot more than once.

470 Mbogo,
Yes I have read your article. I think the rotational velocity differences you generated by varying the velocity from about 2400 to 2500 fps at the muzzle in the same twist rate barrel would not be significant enough to produce any measurable difference. This would be akin to testing a 1 in 12" twist versus a 1 in 12.5" twist rate.

Your data does seem to indicate no "go-to-sleep" effect was detectable over the ranges tested.

We need someone to test something like a 1 in 10" twist versus a 1 in 15" twist rate to see if this produces any differences in penetration at any given range when the muzzle velocity is the same for both barrels.
I will concede Nickudu's guesstimation of no significant effect if I can get some results in such a setup that show no significant effect.

Hopefully Andy's tests will include this kind of spread. If I ever get the chance I will use a 50 BMG with 15 twist compared to my 510 JAB/500 A-Square with a 1 in 10 twist, with both pushing a 570 grain FN GS Custom and 600 grain Barnes solid to the same muzzle velocity (2400-2500 fps).

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Good huntin' and shootin',
RAB

Nickudu,
I think you are correct about the shedding petals thing. I lost petals on X-Bullets only when massive bone was encountered on the water buffalo. With one shot in the humerus and one shot in the vertbral body of a cervical spine vertebra, both lost petals. However, this is a digression from the main topic of interest to me, which is penetration and barrel twist rate.

I will concede your belief of no significant effect when I see significant test results that show no significant effect. Alas, My work gets in the way of my play. One of these days I will do the tests myself in .510 caliber with 10 and 15 twist barrels.

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Good huntin' and shootin',
RAB

I am not looking for "concessions" of any kind from anybody. I am merely offering my opinion. I've been wrong before and will be again.

The creation of a viable test on a limited buget seems a difficult proposition to me.
I believe Paul H. made mention of a concept involving suspended plastic bags of water, of equal capacity, in an effort to eliminate as many variables as possible. This idea has merit, in my view.

It is my feeling that the range of appropriate twist rates in a given caliber are not disparate enough to create a discernable difference in penetration depth.

I remain as interested as anyone else in looking at any hard earned results and wish Andy success.

I did penetration tests on slanted boards 45�, 1.5" thick and each 1 " apart, resin bonded material, no plywood. .458 500 gr conventional FMJ at 100 yards. Vo 2400 f/s. 1:14 twist barrel. I couldn`t observe any deviation from a straight bullet�s path.

The disintegration (streak of smoke) of high speed .224 caliber bullets is not caused by the high rotational speed of the flying bullet, but due to the stress in the barrel during the rotational acceleration.

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Nickudu,
Just to play the devil's advocate, and stir the pot a little more, recall that in my little exposition on the BSI, I opined that I would not include any factor for bullet spin rate because it would probably not amount to much of importance with the commonly available velocities and twist rates of most rifle/cartridge combos.

However, this does leave open the possibility that it may be important in the rare case such as the .458 Winchester. 1 in 14" twist barrels with muzzle velocities below 2150 fps may be the verge of something that could be corrected by just a little more velocity or a little faster twist. That is the hypothesis to be tested.

Another interesting facet of this is the internal ballistics of the faster twist barrel: Do you get higher pressures with the same load in a faster twist barrel? How does this affect the velocity attained with the same load? Do you therefore need to reduce the load with a faster twist barrel? Will you get lower velocity at the same pressure levels and hence get diminishing returns for the faster twist? Could this be why it might be of little significance for practical purposes? I don't know.

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Good huntin' and shootin',
RAB

Bear with my poor memory, but I think Mike LaGrande has fired many a round of heavy bullets in 458 and above in penetration tests and has written a book on the subject. Mike was, or is, some type of Gov't employed hunter in Africa, someone who posts here must know of him? Anyway, I sure would like to find a copy of Mike's book. Now, let's not get into a p------ contest over the A-Square manual, but it has a photo of Mike's test device and a dissertation on twist differences and resultant penetration with bronze solids. Nice theory, but should be backed up with field observations.

RAB,

thanks for your interest.

My test is as follows:

3/4 inch plywood spaced 3/4 inch apart.

three 458 wildcats, one 450 Ackley and two 458 x 404 improved.

Three twist rates, 1-10, 1-12, 1-14.

500 gr Hornady FMJ RN.

2,400 fps and loaded down to 2,050 fps.

Also test 1-8 375 and 1-12 375, 1-12 416 and 1-14 416.

I'll keep you all informed.

Andy

The effect of twist and speed may have a big effect on bullet stabilization, whether the bullet is yawing or not, and at what distance it stops yawing, if it does.

This could have a major (or minor?) effect on penetration. Too bad somebody couldn't afford high speed photography when those tests are done. IF there is any difference in penetration, then bullet stabilization could be a gnawing, unanswered question.

Mike LaGrande worked for the Zimbabwe Parks and Wildlife, problem animal control and I think he also worked for the Tetsi Fly control up north and they do a lot of culling...

the problem with rate of twist, or I'll even broaden that scope by saying rifle barrels is that you can run a dozen off the same thimble and they will all be different...I've seen crooked barrels shoot great and perfect barrels scatter shots, I have seen slow twist shoot both light and heavy bullets both good and bad and visa versa...

Gun barrels are like wimmen, ya just can't figure'm and when you think you have, your in a world of s---t.....

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

Ray, I am in the worldly bucket of evil smelling stuff on both counts!!

I do like George Hoffman's 12 inch twist for the 416's, sure shoot well.

Andy,
That should be very ineresting indeed, and a lot of work for you. It will be greatly appreciated.
Of special interest to me would be how the 500 grain .458 FMJ penetrates at 2050 fps MV from a 14 twist compared to a 12 and 10 twist.
That 8 twist .375 versus a 12 twist should be interesting too, whatever bullet and velocity you use.
I don't think a "go-to-sleep" range is important based on the limited tests 470 Mbogo did, from zero to 50 yards, as I recall.

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Good huntin' and shootin',
RAB

RAB,

I am testing at 30 yards range on the advice of George Hoffman, as that is where he told me a charge might develop on elephant.

the bullets are least stable up close so this is a meaningful test. (I know this from work I did on the 5.45 x 39 and 5.56 x 45 in 1981 at Aberdeen).

My 1-8 twist 375 (300 FMJ) will penetrate 52 inches water compared to 39 inches with 1-12 twist, and I expect similar results in the wood.

I have used this stop box for many years and called it a "light foilage simulator" in my test of military calibers.

Andy

Andy,
It sounds like you already know what the results will show. Some more actual specifics should be gratifying. Sounds like you have some previous experience with this topic that you might be able to generalize about.

Your last post also begs the question of internal ballistic effects of barrel twist rate, based on your general impressions of past shooting and load development:

Can you fire the same loads in both an 8 twist and a 12 twist 375 Whatever?

How do the maximum loads compare in general between a fast twist and a slow twist?

What kind of velocity difference, if any, is there between the fast and slow twist when maximum pressures are obtained in each?

Thanks for any input. I am wasting away in Connecticut.

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Good huntin' and shootin',
RAB