Penetration - velocity vs size

Discussion in 'Ammunition & Reloading' started by planenut, Mar 12, 2010.

  1. planenut

    planenut New Member

    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.

  2. c3shooter

    c3shooter Administrator Staff Member

    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.

  3. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

    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. planenut

    planenut New Member

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

    Jpyle New Member

    Info at link...
    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
  6. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

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

    JonM Moderator


    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. NavArch

    NavArch New Member

    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
    Bad guy body type
    Bad guy clothing type
    Location of bullet impact
    Angle of bullet impact

    This is why bullet designers today use very sophisticated computational fluid dynamics software (think finite element method software that knows about fluid and squishy stuff). You will find all sorts of "percentage one-bullet stop" figures in the open literature. Some of it may be good general trends, but none of it is really solid scientific data. Too many variables.

    Pick something that works well in your firearm and that you think you can have confidence in - and then GET TO THE RANGE. Fire-and-move practice is best. Shot placement is king. Penetration is only queen. Best bet, say the professionals (does not include me) is multiple rounds to Center of Mass until the threat is no longer a threat.