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Thread: A question to Doc - the importance of expansion to incapacitation

  1. #1

    A question to Doc - the importance of expansion to incapacitation

    Doc,

    Assume the numbers below come out of a properly done IWBA standard 4 layer denim test in properly calibrated ballistic gelatin. I'm intentionally not dealing with barrier penetration issues (auto glass, steel, wallboard, etc.)

    Take two 9mm rounds. Both penetrate past 12". For the first hypothetical, they penetrate equally One expands to .5", the other expands to .6" I look at the math of this, calculate the frontal areas of the two bullets, and see that the larger bullet has a 44% larger frontal area. (Note, I'm taking frontal area as a simple circle to calculate area based on diameter.) I take this as giving it 44% advantage in destroyed tissue, and figure this most have some significant increased effect on incapacitating capability. Is this thinking correct, or am I missing something? If it's the latter, what am I missing.

    In the second hypothetical, everything is the same as the first one except penetration. The bullet that expands to .6" will penetrate to 13" While the bullet that expands to .5" penetrates to 16". If I now take the frontal area and multiply by penetration, I get crush cavity volume. The bigger bullet still has an advantage here by about 17%. But the other factor in penetration is that the deeper penetrating round might hit something the shallower penetrating round wouldn't. But given the fact that both meet the minimum standard, which, if either, would have a better chance of a quick incapacitation?

    Let me know what you think. Thanks.

  2. #2
    Site Supporter DocGKR's Avatar
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    Ah....as in most things in life, simple models don't fully reflect the complex variables existing in real life and the question is not answerable with any degree of specificity.

    For example, which projectile has a sharper leading edge and what are the shapes like?

    Name:  40 handgun bullet measurement.jpg
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    All of the above have the same average expansion, but the third one from the left probably offers the most efficient cutting.

    In general, if two handgun projectiles have EXACTLY the same parameters in every other metric, then the one which directly crushes more tissue will tend to be more effective.....most of the time.
    Facts matter...Feelings Can Lie

  3. #3
    Thanks Doc.

    Yes, I realize my analysis might be a bit simplistic. For bullets that expand in a snowflake (for lack of a better term) pattern, vs circular, I take the diameter as the average width of the expanded petals, on the assumption that tissue in the Vs between them will be compromised by the cutting action you describe.

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    Are we making the assumption that all other variables are truly equal or would you consider other variables more important?

    I'd think a difference of .1 inches would lead me to consider which of the two rounds were more accurate or softer shooting in the firearm I chose but that's just me.

    Sent from my moto g(6) using Tapatalk

  5. #5
    Does it some more consequential if it's stated as a 40+% increase in frontal area? I think that's the question, how much difference does this aspect make, so that it could be evaluated against the other characteristics of the round, including the ones that you point out. This also applies to evaluating different calibers.

    It might not be a big deal. I'm not in a position to know. The good doctor is.

    Quote Originally Posted by 45dotACP View Post
    Are we making the assumption that all other variables are truly equal or would you consider other variables more important?

    I'd think a difference of .1 inches would lead me to consider which of the two rounds were more accurate or softer shooting in the firearm I chose but that's just me.

    Sent from my moto g(6) using Tapatalk

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    .1” difference in expansion, by itself, does not strike me as particularly significant. 2 bullets from the same box might have that much variance. Striking a bone vs not striking a bone might cause some variance.

    What I think about more: Does that bullet penetrate to a depth I want for that application? Does it reliably expand? Does it function 100% in the firearm(s) I intend to use it in? Does it hit within an acceptable dispersion from POA from that firearm? If all of those are met, I will not find any purpose in worrying about .1” difference in expansion.

  7. #7
    Quote Originally Posted by BBMW View Post
    For bullets that expand in a snowflake (for lack of a better term) pattern...
    May I recommend the term 'stellate' for describing the expansion of bullets like the HSTs and the Barnes XPBs?
    ''Politics is for the present, but an equation is for eternity.'' ―Albert Einstein

    Full disclosure per the Pistol-Forum CoC: I am the author of Quantitative Ammunition Selection.

  8. #8
    I've never heard that term used before, but, looking it up, it does fit. I wonder how many would actually know what it means.

    Quote Originally Posted by the Schwartz View Post
    May I recommend the term 'stellate' for describing the expansion of bullets like the HSTs and the Barnes XPBs?

  9. #9
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    I would think most damage is done during expansion prior to thepetals folding
    All the back giving a “leading” edge. So are the terminal dimensions of expansion actually
    Incorrectly measuring a more “true” expansion.

    Example, if you fold the expanded petals back to their most open position and then take the measurement, that woul
    Give a larger expanded dimension?

  10. #10
    Site Supporter DocGKR's Avatar
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    Most properly designed handgun projectiles offer full expansion within the first 1-3" of travel in tissue. This has been previously repeatedly proven by shooting thin 3" blocks of properly fabricated tissue simulant and recovering the projectiles.....
    Facts matter...Feelings Can Lie

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