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# Rotational velocity vs wound severity

#8
10-26-2012, 06:40 PM
 Platinum Member Join Date: Jun 2001 Location: Potomac River Posts: 5,088
Re: Rotational velocity vs wound severity

Quote:
 because the bullets are more apt to tumble.
Bullet deformation on impact is important for FMJs!!!!! It screws up the rotation and the bullet loses spin stability.

On an expanding bullet, the center of mass moves forward as the bullet expands creating or adding stability to the bullet. Even in the absence of spin an expanded bullet will be stable passing through a body. Simple physics of the center of mass and stability. It is what archers call Forward Of Center and why an arrow can be stable without spin.
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#9
10-26-2012, 06:53 PM
 Platinum Member Join Date: Dec 2008 Location: rathdrum, id. Posts: 5,266
Re: Rotational velocity vs wound severity

Quote:
 Originally Posted by Buffalobob Bullet deformation on impact is important for FMJs!!!!! It screws up the rotation and the bullet loses spin stability. On an expanding bullet, the center of mass moves forward as the bullet expands creating or adding stability to the bullet. Even in the absence of spin an expanded bullet will be stable passing through a body. Simple physics of the center of mass and stability. It is what archers call Forward Of Center and why an arrow can be stable without spin.
Exactly.....Rich
#10
10-26-2012, 07:00 PM
 Platinum Member Join Date: Dec 2008 Location: rathdrum, id. Posts: 5,266
Re: Rotational velocity vs wound severity

I just located the article written by Adam S. Gubar entitled (terminal ballistics- getting past the bs) It was under (hunting bullet terminal ballistics)
#11
10-26-2012, 07:55 PM
 Platinum Member Join Date: May 2012 Posts: 4,263
Re: Rotational velocity vs wound severity

I was under the impression that rotational velocity slowed in tandem with linear velocity. a bullet turns say 1 turn in ten inches at muzzle, shouldn't it be 1 turn in 10" at some far off range also, or even less since air resistance would act on the land cuts on the bullet surface. And that 1 in 10 inch linear is going to be slower at distance which would slow your rpm down. The two different progressions are locked together in the same ratio via the fixed bore twist. edit- at first anyway.

An easy play on this would be to use two different 22 cal centerfires since different twist rates are so common.

Last edited by Lefty7mmstw; 10-26-2012 at 08:06 PM. Reason: clarification on wording
#12
10-26-2012, 08:01 PM
 Platinum Member Join Date: Dec 2008 Location: rathdrum, id. Posts: 5,266
Re: Rotational velocity vs wound severity

Quote:
 Originally Posted by Lefty7mmstw I was under the impression that rotational velocity slowed in tandem with linear velocity. a bullet turns say 1 turn in ten inches at muzzle, shouldn't it be 1 turn in 10" at some far off range also, or even less since air resistance would act on the land cuts on the bullet surface. And that 1 in 10 inch linear is going to be slower at distance which would slow your rpm down. The two different progressions are locked together in the same ratio via the fixed bore twist. An easy play on this would be to use two different 22 cal centerfires since different twist rates are so common.
The rotational velocity and forward momentum change at a far different rate with rotation winning out. i.e. the forward impact velocity could be down 50% but the rotational velocity is probably still over 90%. There are charts which show this and I don't know exactly what the ratio is, but it is a lot!.......Rich
#13
10-26-2012, 08:05 PM
 Platinum Member Join Date: May 2012 Posts: 4,263
Re: Rotational velocity vs wound severity

Quote:
 Originally Posted by elkaholic The rotational velocity and forward momentum change at a far different rate with rotation winning out. i.e. the forward impact velocity could be down 50% but the rotational velocity is probably still over 90%. There are charts which show this and I don't know exactly what the ratio is, but it is a lot!.......Rich
interesting...
air resistance in play on the forward axis but not as great on rotational.... feels a bit warped doesn't it.
#14
10-26-2012, 09:19 PM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 4,223
Re: Rotational velocity vs wound severity

Normally stability climbs downrange, because displacement per turn(to overcome it) greatly decreases with falling velocity.
So for example, a 10" per 1 turn at the muzzle ends up way less displacement per turn at 500yds.
It ends up ~7.3:1 at 500yds with a 95gr BIB launched at 3kfps in 10tw. And Sg from 1.5 at the muzzle would increase to 2.85 by 500yds.
This reverses trend once nearing mach1.

I know terminal ballistics represents a very complicated science of it's own, and I'm only a varmint hunter. But what I have noticed is that speed of death relates to how much energy is released INSIDE game. This, moreso than the wound itself.
I kill groundhogs far more directly with light bullets that leave no exit wound, than with heavy bullets which make a holy mess of the hogs(like several airborne pieces). I think this is due to hydraulic shock that is REDUCED when a bullet destroys any containment of it. And with this condition the game is allowed to bleed to death. With lighter bullets, releasing full energy that remains inside, the game drops without a twitch(not even a death kick).

I saw this same result(in a video) with an elephant shot in the ass. It dropped instantly without a twitch, seemingly unaware that a relatively tiny ~650gr bullet hit it. This bullet did of course cause fatal damage. But there is no way that damage in itself caused an elephant to instantly drop onto it's belly, all legs outward, with no further movement whatsoever.

Just some thoughts on it. I don't know about jacket integrity on this kind of killing.

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