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Thread: penetration

  1. #1

    Question penetration

    We discuss quite a lot on this subject and it's overwhelmingly believed that the faster a bullet travels, the faster it expands and limits penetration. My question is this...take the same bullet, cal and sd, say fired at 2500fps and it penetrates to x amount of inches, ok? Then, same scenario, but fired at 2900 fps.Would that extra 300 fps equate to x plus inches in penetration or would that extra speed be moot? I would buy that that extra velocity would get a little more penetration...kinda like being jabbed with a blunt object like the end of a baseball bat...eventually, if one got jabbed with enough velocity, it could penetrate right through you, theoretically. So where am I going wrong?

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    Quote Originally Posted by Maydog View Post
    We discuss quite a lot on this subject and it's overwhelmingly believed that the faster a bullet travels, the faster it expands and limits penetration. My question is this...take the same bullet, cal and sd, say fired at 2500fps and it penetrates to x amount of inches, ok? Then, same scenario, but fired at 2900 fps.Would that extra 300 fps equate to x plus inches in penetration or would that extra speed be moot? I would buy that that extra velocity would get a little more penetration...kinda like being jabbed with a blunt object like the end of a baseball bat...eventually, if one got jabbed with enough velocity, it could penetrate right through you, theoretically. So where am I going wrong?
    OK, Iíll bite:
    The bullet that was (400) fps faster would penetrate less if it didnít fail to expand.

    If you jabbed the baseball bat with enough velocity it would splinter, before penetrating right through you.

    Smitty of the North

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    Quote Originally Posted by Maydog View Post
    We discuss quite a lot on this subject and it's overwhelmingly believed that the faster a bullet travels, the faster it expands and limits penetration. My question is this...take the same bullet, cal and sd, say fired at 2500fps and it penetrates to x amount of inches, ok? Then, same scenario, but fired at 2900 fps.Would that extra 300 fps equate to x plus inches in penetration or would that extra speed be moot? I would buy that that extra velocity would get a little more penetration...kinda like being jabbed with a blunt object like the end of a baseball bat...eventually, if one got jabbed with enough velocity, it could penetrate right through you, theoretically. So where am I going wrong?
    All depends on bullet construction. For example, a solid bullet won't expand. So, take two solid bullets of the same caliber, but one with greater SD than the other. In this case, the one with greater SD has the potential for more penetration than the other one. However, you can improve the penetration potential of the one with lesser SD by increasing its velocity. With expanding bullets it's possible to accomplish the same, but again, all depends on bullet construction, since some bullets are designed to expand fast, while others are designed to expand gradually (controlled-expansion bullets).

    You can take two similarly constructed bullets, lest say...two 30-caliber Partition bullets, one of 180 grains and the other of 200 grains. In this case, the one with greater SD has the potential for greater penetration than the other. You can push the one with lesser SD for greater penetration, or by getting closer to the target (higher speed), but only to a point. This point is reached at a velocity increase where an expanding bullet can blow apart when it hits the target.

    Lets say that you take a 30-caliber 190-grain Partition, and a 180-grain X bullet of the same caliber. In this case, the Partition with its greater SD has the potential for deeper penetration, but the X bullet is designed tougher, therefore offsetting the SD concept. The problem is finding out exactly at what point the X will out-penetrate the heavier one, but I imagine that it can be done at a lab.

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    Quote Originally Posted by Maydog View Post
    We discuss quite a lot on this subject and it's overwhelmingly believed that the faster a bullet travels, the faster it expands and limits penetration. My question is this...take the same bullet, cal and sd, say fired at 2500fps and it penetrates to x amount of inches, ok? Then, same scenario, but fired at 2900 fps.Would that extra 300 fps equate to x plus inches in penetration or would that extra speed be moot? I would buy that that extra velocity would get a little more penetration...kinda like being jabbed with a blunt object like the end of a baseball bat...eventually, if one got jabbed with enough velocity, it could penetrate right through you, theoretically. So where am I going wrong?
    Your question and your analagy are good ones and I'm glad to see something here besides armed teachers.

    As you have discribed here the exact same bullet, weight and construction, considering it is a bullet designed to expand, the faster bullet will likely penetrate less, but will leave a larger impact crater. (larger wound channel)

    I think what a lot of folks don't realyze is that an expanding bullet expands all it is going to at impact or very shortly after. Basically, a bullet of a certain design, when it impacts a certain media (animal tissue) at a given velocity, it will expand to it's maximum in a certain period of time. This time is very short and would equate to about 2-3" of bullet travel. Then after this expansion, it will penetrate based on it's momentum and of course the tissue it travels through and its frontal resistance (size of the front end). Momentum is bullet weight * remaining velocity. If it has expanded to a large size, with a given momentum, etc., it will slow more rapidly. If a smaller size it will have less frontal resistance and give up it's remaining velocity more slowly, thus penetrate deeper. This is why heavier bullets penetrate deeper. They have more momentum and if in the same caliber, will generally have lower impact velocities.

    A key point here is; Expansion is a product of energy at impact (m/2*v*v) and penetration is a function of momentum. (m*v) With your analagy above, the higher velocity bullet will have greater energy.

    Some hunters want the bullet to remain in the animal as evidence that the animal has absorbed all the energy of the projectile. This is fine as long as it does penetrate deep enough to reach the vitals from any angle that a shot may be taken. There is however no indication at all that an animal expires sooner if it "catches" the bullet. Actually quite the opposite, an animal with holes in both lungs and open wounds on each side will definately expire sooner regardless of which bullet/caliber it is hit with. Two sucking chest wounds and two holes leaking blood will always bring about a quick demise.

    There is no way to totally predict how a bullet will behave at impact on an animal, there are only general expectations. Some bullets are obviously more strongly constructed than others, all else equal (same caliber/weight/sd/shape), they will penetrate better than a more lightly constructed bullet.

    One of the problems with expanding bullets is we really don't know the answer to the question; How much will it expand when it hits mr. moose at a velocity of x fps. Also even if the manufacturer does give the best expansion velocity, we don't know the velocity because it is range (distance) dependent. So when we choose a bullet we want one that has a broad range of expansion velocity and is matched to the rifle we are using. Certainly a 300 RUM firing a 150 grain standard cup and core bullet at 3400 fps will expand way too fast (disintegrate at impact) where the same bullet fired from a 300 Savage at 2600 fps will do quite well. It will expand and penetrate in a very good compromise between the two. On the opposite end of the spectrum, the 300 Savage with a 165 grain Barnes TSX, will probably make that bullet perform like a solid but the RUM will expand it and push it through.

    These are generalities and offer a basis for bullet selection. What's important here is that we go in the right direction to achieve the desired results. That direction for penetration is ...Heavier, slower, stronger built bullets.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  5. #5

    Talking bat

    Quote Originally Posted by Smitty of the North View Post
    OK, Iíll bite:
    The bullet that was (400) fps faster would penetrate less if it didnít fail to expand.

    If you jabbed the baseball bat with enough velocity it would splinter, before penetrating right through you.

    Smitty of the North
    Thanks, but I just used the bat as an example, and you could be right, but not to get too sidetracked, I know that tornados have driven posts, staubs, straw. boards, limbs, etc right thru people, animals. telephone poles,etc. But back to my original question. I guess what I can assume is that two blunt objects of the same diameter, weight, etc (say a solid) hitting the same medium, the faster of the two would not penetrate any appreciable amount deeper? Velocity increases, beyond a certain point, yields very little in terms of penetration...like the faster it goes, the faster it slows down...kinda like a shotgun pellet?

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    Quote Originally Posted by Maydog View Post
    But back to my original question. I guess what I can assume is that two blunt objects of the same diameter, weight, etc (say a solid) hitting the same medium, the faster of the two would not penetrate any appreciable amount deeper? Velocity increases, beyond a certain point, yields very little in terms of penetration...like the faster it goes, the faster it slows down...kinda like a shotgun pellet?


    Now wait a minute here. When we speak of a solid or any non expanding bullet, things change. That's why I specified soft point, expanding bullets in my lengthy dissertation above. Solids of equal weight/caliber/shape/construction/sd and changing only impact velocity then the bullets with the highest momentum will sink deeper. Just like above except the bullet will remain unaltered in shape after impact. And, of course the higher velocity has greater momentum. Now the limiting factor becomes terminal stability. (Will the projectile become unstable after impact?) A bullet that turns sideways cannot be expected to penetrate like a spear.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



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    Default penetration

    years ago Finn Aagard had an article that I thought rather interesting.
    Using DRY phone books he tested various bullets and loads, deeper the penetration the better, specifically testing for bullet performance for tough game, dangerous game.
    I never would have thought of dry phone books, I have always used wet and I mean wet phone books. Expansion channels were really neat, 50 and 100 yards.
    So, all ballistic discussion aside; and I love ballistics, heck try the bullets out in dry phone books! see what happens.
    Since financial constraints prohibit testing for me, I would love to see someone with time and MONEY try it out.
    Penetration for big bear , would love to see the results.

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    Default penetration

    For those who don't know me, I am the .264 Swede nut, have tried the 159 and 160 and other bullet weight and was shocked with the results, even after reviewing the S.D. for the bullets it was still quite impressive.
    The 160 Hornady just passed thru 3 dry phone books, did not have any more books to line up, would probably need 4or 5.

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    Default penetration

    Predicting bullet penetration is VERY complex as I remember. There are at least three general formulas involved depending upon impact velocity and any number of permutations of each for any predictive analysis. I imagine that is why so much experimental testing is done for this type of thing. Generally, the drag or friction force which limits penetration of any projectile if that projectile is going very fast at all (like a bullet) is geometrically proportional to the velocity. A VERY general rule is that friction or drag force (resistance to penetration) is quantitatively proportional to the square of the velocity. So.... as the velocity increases the "resistance to penetration" increases by a squared factor. So.... a monolithic, hard, strong, non-deforming bullet with a momentum (vel x mass) based on an impact velocity of say 2000 fps will penetrate "X" number of inches into a certain material. And... an identical bullet with a momentum based on a velocity of 4000 fps (twice the momentum of the first bullet) will penetrate "Y" number of inches into the same material. BUT..... it will not penetrate twice the number of inches ("Y" will be substantially less than twice "X" inches). Because... the resistance to penetration is proportional to the square of the velocity. Add to this very complex subject the bullet's rotational component and basic stability, as Murphy pointed out, and it gets even more complex.... this based on memory from at least thirty years ago so it may be all wrong but I think that's the way this physics works?

  10. #10

    Talking complex?

    Man, you guys explaining this (quantum physics?) made me so dizzy, I fell off my chair, but because of my mass and low momentum, thankfully, I never penetrated the floor very far. I'm understanding what you're saying...just using the wrong examples to explain myself. Thanks.

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    Default penetration

    Dear May Dog, aw heck, just shoot some darn phone books! I am fascinated by the question, I may actually try this with the 140 pspclkt, 2400 fps then my favorite handload at 2891 fps, gonna need a bunch of phone books though.
    Not very scientific but may provide some theories

  12. #12

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    GREAT DISCUSSION I LIKE IT. Now that is why I use a 30-06 200gr SBT, It just simplifies all of the calculations and drops game dead in their tracks from deer to bear with a hole in one side and out the other side. It gives me a balance of energy and momentum and I want them both to be significant and balanced. Energy tears up things and momentum takes the energy to the deep places if not all the way through. I know this is a simple conclusion and it saves me the mental effort of going into internal ballistic, external ballistics and terminal ballistics, bullet construction and cartridge but it works.
    A GUN WRITER NEEDS:
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  13. #13

    Question simple

    Quote Originally Posted by beartooth View Post
    GREAT DISCUSSION I LIKE IT. Now that is why I use a 30-06 200gr SBT, It just simplifies all of the calculations and drops game dead in their tracks from deer to bear with a hole in one side and out the other side. It gives me a balance of energy and momentum and I want them both to be significant and balanced. Energy tears up things and momentum takes the energy to the deep places if not all the way through. I know this is a simple conclusion and it saves me the mental effort of going into internal ballistic, external ballistics and terminal ballistics, bullet construction and cartridge but it works.
    I hear ya bear...plus it keeps one from getting dizzy and passing out. It amazes me the amount of technical intelligence there is on this forum, don't it you? I would also like to know(I can't leave well enough alone) if the penetration would always be the same for different caliber bullets, but of the same construction and sectional density and velocity?

  14. #14

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    Quote Originally Posted by Maydog View Post
    I hear ya bear...plus it keeps one from getting dizzy and passing out. It amazes me the amount of technical intelligence there is on this forum, don't it you? I would also like to know(I can't leave well enough alone) if the penetration would always be the same for different caliber bullets, but of the same construction and sectional density and velocity?
    NO! If the velocity was the same and construction the same and also the sec. density was the same, the frontal area and weight of the bullets of different cal. would be different and their momentum would be different as well as different levels of drag as the bullets would open up differently and many other variables and other factors.
    A GUN WRITER NEEDS:
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    Quote Originally Posted by beartooth View Post
    NO! If the velocity was the same and construction the same and also the sec. density was the same, the frontal area and weight of the bullets of different cal. would be different and their momentum would be different as well as different levels of drag as the bullets would open up differently and many other variables and other factors.
    Yes, Zackly!

    Except for one thing; If your quote is from Quigley, he said "You ain't Bill Hickock and this ain't Dodge City"
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    Quote Originally Posted by beartooth View Post
    Energy tears up things and momentum takes the energy to the deep places if not all the way through.
    That's it, I like that.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  17. #17

    Talking sd

    I don't know why, but I've always had the impression that bullets with the same sd would penetrate the same. I'm sure someone told me that years ago and I just never questioned it, but you folks straightend me out. Gotta be global warming! Thanks.

  18. #18

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    Quote Originally Posted by Murphy View Post
    Yes, Zackly!

    Except for one thing; If your quote is from Quigley, he said "You ain't Bill Hickock and this ain't Dodge City"
    Hey thanks I did get the quote wrong
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    Quote Originally Posted by Maydog View Post
    I don't know why, but I've always had the impression that bullets with the same sd would penetrate the same. I'm sure someone told me that years ago and I just never questioned it, but you folks straightend me out. Gotta be global warming! Thanks.
    Hold on...there's more of this.

    Sectional Density is the weight of the bullet (in pounds) /the square of the diameter. So the larger frontal area of one bullet is compensated by the greater weight (in order to have same SD, if it has larger in diameter, it must have more weight) If impact velocity is the same for any two different sized bullets (with same SD), then the momentum is higher for the heavier one.

    The other factor would include the drag from the larger surface of the nose and sidewall friction. This larger bullet will make a larger wound cavity but an actual penetration comparison can't be made with out controlled tests.

    We cannot prove nor predict bullet behavior with mathmatics, and I'm pretty good with math.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  20. #20

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    Quote Originally Posted by Murphy View Post
    Hold on...there's more of this.

    Sectional Density is the weight of the bullet (in pounds) /the square of the diameter. So the larger frontal area of one bullet is compensated by the greater weight (in order to have same SD, if it has larger in diameter, it must have more weight) If impact velocity is the same for any two different sized bullets (with same SD), then the momentum is higher for the heavier one.

    The other factor would include the drag from the larger surface of the nose and sidewall friction. This larger bullet will make a larger wound cavity but an actual penetration comparison can't be made with out controlled tests.

    We cannot prove nor predict bullet behavior with mathmatics, and I'm pretty good with math.
    How right you are, that is why what we see work in the field is the most important thing. DOES IT WORK? And that really can only been proven in the field. That is why I think that a cartridge that moves at respectable velocities and bullets that work well at those velocities with sufficent weight to have momentum so as to transfer the energy over a great area and depth in or through the target is what a hunter should want. And when that is done on a consistent bases and the desired effect is achived "DON'T FIX WHAT AIN'T BROKE!!! Keep using it!
    A GUN WRITER NEEDS:
    THE MIND OF A SCHOLAR
    THE HEART OF A CHILD
    THE HIDE OF A RHINOCEROS

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