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Rotational velocity vs wound severity

 
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Old 10-26-2012, 01:19 PM
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Rotational velocity vs wound severity

I've decided to start this thread because I feel there is need to know "why something happens", not just that it occurs. As most of you already know, I make my own bullets and do a lot of testing, which makes this of particular interest to me, but applies to everyone who hunts. Recently, I tested some 215 Berger Hybrids for the purpose of hunting application. My goal was to ascertain what minimum expansion velocity was with this bullet to apply to long range hunting. I did this using reduced velocity loads fired point blank into water, which I have found to be a good testing media. The results were not what I had hoped for with more velocity needed than what I consider good long range performance. Brozs' testing on real life targets does not seem to duplicate what I found in my testing, and I am confident that water testing is not the problem! I have come to the conclusion that the rotational velocity difference between the reduced load, and a full throtle load, may well be the difference. How much is due to the rotation itself, or the additional expansion caused by the rotation, is what I would like to discover. I have done a little research and have found there are others who feel that rotation is definitely a factor. Adam gubar, whom I think wrote for Chuck Hawks, addressed this. If I can find it, there was an article written by the military years ago comparing damage between the M1 carbine and M1 rifle, both firing 110 grain bullets, the former point blank with a 16" twist and the later firing at a range to duplicate the impact velocity but with a full throtle load with a 10 twist. The resulting damage with the 10 twist was considerably greater! This was done in the ballistic gel which was used at the time. I'm not sure when I will get the time, but my plan is to perform the same type of test, only use the same rifle, one with a reduced load, and one with a full load but at long range. This should eliminate some of the variation which should be expected from different rifles. The rotational velocity does not decrease nearly as fast as forward momentum, so this should work. Also, I want to test both full jacketed vs expanding bullets, which should give a good indication of how much of the difference is due to expansion, and how much is due to the rotational energy itself. Besides the evidence of what I have read over the years, my personal experience tells me that there is evidnce of "more twist, more damage"! Some of this no doubt is due to twist on the integrity of the bullet jacket, but I think there is more to it than that. I welcome everyone to research this some more, which I intend to do, and post what they find........thanks/Rich
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Old 10-26-2012, 01:59 PM
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Re: Rotational velocity vs wound severity

I expect your thought process will be proven correct. Higher rotational velocity will result in greater bullet expansion, given equal impact velocities. And even if bullet expansion is not increased, I still believe the wound channel and trauma caused by an expanded bullet rotating at the higher RPM will result in greater tissue damage as the expanded edges of the bullet rotors through flesh and organs.
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Old 10-26-2012, 04:29 PM
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Re: Rotational velocity vs wound severity

Watch some videos of bullets entering gel. They seem to make only a couple of revolutions.

I got chewed out pretty well by posting results of expansion tests using reduced loads to get LR velocity @ 200 yds.

People jumped all over the reduced spin rate.

Personally I don't think it makes a squat of difference.
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Old 10-26-2012, 04:46 PM
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Re: Rotational velocity vs wound severity

Jacket integrity and structural integrity are a big factors for the heavy for caliber bullets with thin jackets that are spun at high rpms.

FMJs that are are at marginal stability (rpm) produce larger wounds than highly stable ones. This has been well documented by the military trauma doctors.

The question you inquire about has many different answers that depend upon the initial construction of the bullet.

There is an old thread by Buffalorancher that has some intelligent remarks in it and one excessively stupid one near the end. Watching Youtube cartoons when you can't fathom high school geometry has its problems.
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Old 10-26-2012, 05:49 PM
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Re: Rotational velocity vs wound severity

Quote:
Originally Posted by Buffalobob View Post
Jacket integrity and structural integrity are a big factors for the heavy for caliber bullets with thin jackets that are spun at high rpms.

FMJs that are are at marginal stability (rpm) produce larger wounds than highly stable ones. This has been well documented by the military trauma doctors.

The question you inquire about has many different answers that depend upon the initial construction of the bullet.

There is an old thread by Buffalorancher that has some intelligent remarks in it and one excessively stupid one near the end. Watching Youtube cartoons when you can't fathom high school geometry has its problems.
I suspect the marginal spin produces more trauma because the bullets are more apt to tumble. Unexpanded bullets also seem to tumble more. I I have found SMK's are worse than VLDs for not expanding, which also causes worse tumbling and banana bullets. This happens nearly everytime when a SMK doesn't expand. I believe this is caused by the greater angle ogive not allowing expansion to start as easily. Also, it would not surprise me at all if the Bergers which are causing larger exit holes at low velocity are the result of tumbling rather than expansion. Obviously, there is no proof on my part because the bullets are not recovered........Rich
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Old 10-26-2012, 06:20 PM
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Re: Rotational velocity vs wound severity

Rich,
So I can verify I understand your test method... you want to test the same bullet at the same impact velocity but with different RPM's to compare what happens. To do this you'll fire a reduced load at close range to achieve an impact with a velocity of "x" with a low RPM compared to a standard load that you'll shoot at long range to achieve the same impact velocity but higher RPM's. Is my understanding correct?

I'm excited to see what your results are.
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Old 10-26-2012, 06:26 PM
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Re: Rotational velocity vs wound severity

Quote:
Originally Posted by Browninglover1 View Post
Rich,
So I can verify I understand your test method... you want to test the same bullet at the same impact velocity but with different RPM's to compare what happens. To do this you'll fire a reduced load at close range to achieve an impact with a velocity of "x" with a low RPM compared to a standard load that you'll shoot at long range to achieve the same impact velocity but higher RPM's. Is my understanding correct?

I'm excited to see what your results are.
That is exactly right!
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