Stopping Power Measurement


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Old 02-08-2012, 10:52 PM   #1
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Default Stopping Power Measurement

Do we look at velocity or energy? I am looking at the specs for .357 sig and 10 mm auto on wikipedia.



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Old 02-08-2012, 11:44 PM   #2
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velocity and weight = energy



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Old 02-09-2012, 12:36 AM   #3
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Default The Hatcher Formula

The Hatcher Formula is an attempt to mathematically evaluate the approximate effectiveness of pistol ammunition at incapacitating a person. Developed by Gen. Julian Hatcher in the 1930's, it uses the bullet momentum, frontal area, velocity, and a 'form factor.'

The formula is:

RSP = M * A * F

Where RSP = Relative Stopping Power Index, M = Momentum of the bullet in foot pounds, A = Area of the bullet in square inches, F = Form factor derived from his observations with some additions for later bullet types.

http://www.abaris.net/info/ballistics/hatcher-table.htm

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Old 02-09-2012, 01:40 AM   #4
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The following article sort of rambles on and is pretty long, but it will raise some questions in your mind that you'll want to consider as you further ponder your original question.

http://www.gunthorp.com/Terminal%20Ballistics%20as%20viewed%20in%20a%20mor gue.htm

This article was previously posted in another thread on this Forum.

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Old 02-09-2012, 05:51 PM   #5
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The truth is that no handgun round has reliable stopping power, without a CNS hit.

Rifles are a bit different, as Roy Weatherby learned shooting hundreds of head of cattle in carefully controlled experiments. Velocity was the deciding factor, but in order for the velocity to become the deciding, it had to exceed 2650-2700 FPS in order to generate hydrostatic shock.

Those of us old enough to remember the Russian-Afghanistan war, remember the Afghans complaining to the U.N. that the Russians were using "poison" bullets.

That was when the Soviet Union switched from the large, heavy 7.62X39 in the AK-47 to the light, fast 5.45X39 in the AK74. The increase in lethality of the smaller, higher velocity round was very dramatic.

In reality, momentum is a meaningless figure, since it gives equal weighting to mass and velocity, rather than factoring in the square of the velocity. (energy). Even energy has little effect compared to velocity.

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Old 02-10-2012, 01:49 AM   #6
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Quote:
Originally Posted by hiwall View Post
velocity and weight = energy
According to Wikipedia: Kinetic energy = 1/2Mass x Velocity squared.
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Old 02-10-2012, 02:48 AM   #7
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Quote:
Originally Posted by roscoguy View Post
According to Wikipedia: Kinetic energy = 1/2Mass x Velocity squared.
Correct formula. Makes it easy to see why "momentum" is a meaningless measurement.
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Old 02-10-2012, 03:16 AM   #8
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Quote:
Originally Posted by locutus View Post
Correct formula. Makes it easy to see why "momentum" is a meaningless measurement.

Are you suggesting that Newton's Laws are all wrong?
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Old 02-10-2012, 04:29 AM   #9
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Quote:
Originally Posted by heavygargoyle View Post
Do we look at velocity or energy? I am looking at the specs for .357 sig and 10 mm auto on wikipedia.
I like Taylor Knock Out or TKO

TKO = Bullet Mass (gr) x Expanded Bullet Diameter (in) x Terminal Velocity (fps) / 7000

or momentum x expanded diameter

Taylor first described this measure of stopping power in his classic work "African Rifles and Cartridges." Taylor referred to number generated by the equation as the "Knock Out Value" or "Strike Energy." Common practice today is to refer to this value as the "Taylor KO factor" or simply "Taylor KO."

The TKO has no physical meaning and is strictly used as a figure of merit for comparing cartridges. Its main advantage is the ability to attempt to represent complex terminal ballistics as a number; specifically momentum x expanded diameter. This can be utilized to assign different wounding capabilities to projectiles.

It does have good general correlation. For example, the TKO of a .22Mag is about 2, a .38Spcl about 6, a .357 about 10, the 10mm, .44Spcl and .45acp all about 13, a .44Mag 17 and a .454Casull at least 30. Clearly the TKOs are, at least loosely, tracking stopping power. You can't really say that about energy because a .22Mag produces more energy than a .380acp AND a .38Spcl. Momentum works a little better but still has problems: .22Mags and .380acps have about the same momentum and some .38Spcl+Ps have more momentum than .357Mags.
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Old 02-10-2012, 04:30 AM   #10
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Quote:
Originally Posted by Jeepergeo View Post
Are you suggesting that Newton's Laws are all wrong?
I suspect not, just that momentum is not an entirely meaningful estimate of stopping power (it's also not meaningless, just imperfect).


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