# Penetration - velocity vs size

1. ### planenutNew Member

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Assuming the same gun, A Kimber Ultra Elite 45ACP for example, If two different bullets have the same energy but different weights, will penetration be the same?

Federal Hydra-shok:
Grain velocity energy
230 900 414
165 1060 412

On the one hand, it seems the faster bullet would penetrate deeper. But, on the other hand, it seems like it would take the same amount of energy to stop both assuming the diameter is the same and no difference in expansion.

Thoughts?

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Energy is velocity SQUARED times mass. Howver, in terms of penetration, is the faster bullet more likely to expand on impact? If so, It may penetrate less- bullet is getting WIDER.

In general, for penetration, you need weight to retain the energy. Which is why I deer hunt with a .357 with VERY heavy bullets. The little 110 gr- 125 gr JHPs are not gong thru Bambi like a 200 gr solid.

If you are dealing with traditional expanding hollow point bullets, the faster it is going the faster it will expand. A light fast bullet (.45ACP 185gr @ 1100fps) will expand more quickly than a slower heavy bullet (.45 ACP 230gr @ 850fps). As the bullet expands, it loses energy, gains frontal area, and slows down. As it loses energy/momentum and slows down it loses its ability to penetrate deeply.

4. ### planenutNew Member

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So if I had a FMJ bullet, assuming no expansion, Would the penetration differ?

5. ### JpyleNew Member

Terminal Ballistics

Money phrase:
If two projectiles have the same energy, then the heavier will have the greater momentum. "One can think of energy absorption (of a target) as Force x Distance, and momentum absorption as Force x Time. Hence, the heavier but slower bullet with the same energy will travel the same distance in the absorbing material, but because of larger momentum, will take a longer time doing it. It will therefore also impart a greater "kick" to the absorber object."

Last edited: Mar 12, 2010

Yes. That is why most LEO's carry HP ammo. Partially to prevent overpentration.

7. ### JonMModerator

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there is a lot more to it than what your asking. it really depends more on what your intending to do witht he bullet when it is fired.

target shooting/plinking doesnt matter what type of bullet or how fast or how heavy.

personal defense the biggest wound channel you can make is the most important factor.

hunting through and through penatration at your chosen distance with a large wound channel and little damage to edible meat. is what your looking for.

my 1911 is loaded with 230grn hollowpoints. if the thing expands goody gumdrops. if it doesnt i still got 230 grains of lead going through the target. 165 grn bullet better hope you dont hit something that will deflect it and hope the hollow point doesnt get clogged with debris and actually expands. lots of hope riding on a maybe bullet weight.

just my opinions.

8. ### NavArchNew Member

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World's Hardest Firearm Question

I think you may have asked the world's hardest firearm question. Some of the variables are:

Bullet weight
Bullet ballistic coefficient
Bullet internal geometry and materials
Muzzle velocity
Range