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Thread: Some Thoughts on Airgun Killing Power

  1. #1
    Moderator rsterne's Avatar
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    Some Thoughts on Airgun Killing Power

    I've been playing with some numbers this afternoon, and I'll throw this idea out there just for discussion.... It is similar to the long standing idea of having a minimum of 1 FPE of energy per pound of body weight of the target.... I am a firm believer in the relationship between momentum and killing power.... While things like the Meplat diameter affect the diameter of the wound channel, and the sectional density (or the sectional density but using the meplat diameter instead of the caliber) affects the penetration.... you still have to hit an animal hard enough to kill it.... and the bigger it is, the harder you have to hit it....

    The momentum of a bullet at impact is the weight in lbs. times the velocity in fps.... That works out to the weight in grains divided by (7000 times 32.4) times the velocity in fps.... ie W (gr.) x V (fps) / 226,800.... The resulting number would be about 0.8 for a 200 gr. bullet travelling at 900 fps.... pretty hard to relate to the weight of an animal.... If instead of dividing by 226,800 we divide by 1000, the number is now 180.... hmmmmmmmmm.... would a 200 gr. bullet travelling at 900 fps (at impact) drop a 180 lb. animal?.... I would think that would be pretty close....

    Here are some other examples....

    8 gr. @ 450 fps = 3.6 lbs (low powered .177)
    8 gr. @ 900 fps = 7.2 lbs (high powered .177)
    16 gr. @ 900 fps = 14.4 lbs (high powered .22)
    30 gr. @ 900 fps = 27 lbs (high powered .25)
    40 gr. @ 1200 fps = 48 lbs (eg. .22 LR rimfire)
    78 gr. @ 900 fps= 70 lbs (low powered 9mm)
    158 gr. @ 900 fps = 142 lbs (high powered 9mm)
    230 gr. @ 900 fps = 207 lbs (low powered .45 cal)
    170 gr. @ 2000 = 340 lbs (eg. 30/30 Winchester)
    450 gr. @ 900 fps = 405 lbs (high powered .45 cal)
    220 gr. @ 2500 = 550 lbs (eg. 30-06 Springfield)
    570 gr. @ 2000 = 1140 lbs (eg. .500 Nitro Express)

    I think those numbers are fairly realistic, maybe a bit on the low side.... Want to make it even simpler?.... How about if you have an air rifle that shoots in the high subsonic (say 900-950 fps) you just use the bullet weight in grains for the animal weight in pounds....

    8 gr. pellet - 8 lbs.
    16 gr. pellet - 16 lbs.
    30 gr. pellet - 30 lbs.
    100 gr. bullet - 100 lbs.
    200 gr. bullet - 200 lbs.
    400 gr. bullet - 400 lbs.

    Since we have pretty much found out over the years that we don't want to push velocities over about 1000 fps (but we want to get close).... could you ask for a simpler guide to killing power?.... Incidently, at 950 fps, the energy is 2 FPE per gr. of pellet weight.... so we have values about twice the bare minimum FPE if you go by the above numbers....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  2. #2
    Administrator AirGunEric's Avatar
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    Hmm- now what are these 180lb "animals" Bob speaks of... I hope we're not part of something illicit being plotted here.
    I'd say I care- but I'd probably be lying...


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    Senior Member remtom1200's Avatar
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    I wish Squirrels were 18 lbs.
    For every mile of road, there's two miles of ditch

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    Senior Member remtom1200's Avatar
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    Now that I Think about this I am thinking this idea of bigger squirrels may not be good. Down range velocity would become an issue?
    For every mile of road, there's two miles of ditch

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    Senior Member SeanMP's Avatar
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    Nice work Bob

    I'm a big fan of "rules of thumb"
    Sean

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    So...

    You're saying that a .50 BMG is too much for a squirrel... So that's what I've been doing wrong...

    Awesome work on the numbers Bob.

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    Moderator poil27's Avatar
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    great i just hope all the unetihcal hunters out there read this

  8. #8
    Senior Member remtom1200's Avatar
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    That is an interesting and simple guide to keep in mind
    For every mile of road, there's two miles of ditch

  9. #9
    Senior Member Doc Sharptail's Avatar
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    Quote Originally Posted by rsterne View Post
    I've been playing with some numbers this afternoon, and I'll throw this idea out there just for discussion.... It is similar to the long standing idea of having a minimum of 1 FPE of energy per pound of body weight of the target.... I am a firm believer in the relationship between momentum and killing power.... While things like the Meplat diameter affect the diameter of the wound channel, and the sectional density (or the sectional density but using the meplat diameter instead of the caliber) affects the penetration.... you still have to hit an animal hard enough to kill it.... and the bigger it is, the harder you have to hit it....

    The momentum of a bullet at impact is the weight in lbs. times the velocity in fps.... That works out to the weight in grains divided by (7000 times 32.4) times the velocity in fps.... ie W (gr.) x V (fps) / 226,800.... The resulting number would be about 0.8 for a 200 gr. bullet travelling at 900 fps.... pretty hard to relate to the weight of an animal.... If instead of dividing by 226,800 we divide by 1000, the number is now 180.... hmmmmmmmmm.... would a 200 gr. bullet travelling at 900 fps (at impact) drop a 180 lb. animal?.... I would think that would be pretty close....

    Here are some other examples....

    8 gr. @ 450 fps = 3.6 lbs (low powered .177)
    8 gr. @ 900 fps = 7.2 lbs (high powered .177)



    Bob
    Let's not get any misconceptions going here- it will save a lot of actual "in the field" grief...

    First off, a pellet is a pi$$ poor projectile to hunt with- especially at the lower end velocities alluded to at the start of the list. If you aren't capable of head shots at those low velocities, don't shoot. Those low velocity numbers in .177 are extremely marginal on live game- anything other than a head shot will result in a wounded animal on the run or fly.

    I think we need to see more on terminal ballistics- how various projectiles behave on impact. Most pellets I've seen at low to mid range velocities are over-penetrators- they simply pass through the game without expanding... a precise hit in the vitals, or head becomes the absolute minimum requirement.

    Your numbers make more sense to me in the .30 cal/9mm range and up- they equal what is seen from most powder burning handguns.

    Regards,

    Doc Sharptail
    "Ain't No Half Way"

    -S.R.V.

  10. #10
    Moderator rsterne's Avatar
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    I think you are absolutely correct when it comes to the lower velocities.... Consider, however, that even at 450 fps the numbers quoted meet the 1 FPE per lb. of body weight recommended for many years as a minimum.... and at 900 fps they are 2 FPE per lb..... No question that at 1 FPE per lb. you need to be able to make a head shot or you shouldn't be taking the shot.... Any of these "rules of thumb" break down when pushed to unreasonable limits.... Even the famous Taylor Knockdown Formula says that a baseball thrown by a professional pitcher has greater knockdown power than a .500 Nitro Express.... I don't think many great white hunters would consider that a suitable projectile for hunting elephant, however....

    It is interesting that you should mention that over-penetration occurs at low velocities and offer that as an argument against my suggestion for the lower powered guns.... That very penetration is considered an advantage by those that argue for the effectiveness of .177 pellets on larger game such as Racoons, providing the shot penetrates the fuse box.... Far from being unethical hunters, these individuals study the anatomy of their prey, and take into account the angle of the shot and the bone structure in the way before pulling the trigger.... While I'm not good enough to even try dropping a 'coon with any .177, their string of 1-shot kills (and lack of wounded animals) is impressive....

    There is no question that shot placement is King.... and especially with the limited power of an airgun.... It was not my intention to argue otherwise....

    Bob
    Last edited by rsterne; Apr 04 2012 at 09:29 AM.
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

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