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Thread: Dumping energy

  1. #1

    Dumping energy

    As some may recall I don't buy into the idea of a bullet "dumping energy" into a deer and thus causing shock or some other effect which makes the deer fall over. I believe, and I'm far from qualified in this area so this is merely a belief, that deer are made dead by the bullet doing significant damage to internal organs such that blood pressure drops quickly and that puts and end to them. I don't believe that doing this damage takes a lot of energy though I accept that there is a temporary wound cavity that is bigger than the permanent one.

    Some time back, in a most interesting discussion we had on this subject, I expressed the view (with no science to support it) that a significant proportion of the energy "used" by the bullet in passing through a deer was in fact used to deform the bullet. Recently I've been viewing the slow motion video of bullets hitting a metal plate with some interest.

    I've noticed that where the plate is thick enough such that the bullet can not penetrate it then the bullet suffers considerable deformation and, basically, stops dead. I have also seen this in events such as cowboy action shooting where metal plates are often used as targets. As the metal plate is not deformed in any significant way it looks to me as if almost all the energy involved is used in the deformation of the bullet and this gives me cause to consider that this might offer some support for my position that bullets which "dump energy" in deer are actually just using the energy to deform and are doing little or no extra work to the deer than a bullet which is not considered to "dump energy" in the deer. I'm suggesting that bullets which are said to "dump energy" are actually not doing any more damage to the deer than bullets which are considered not to "dump energy" in the target animal, they merely have a construction which causes them to deform such that this deformation uses a lot of energy.

    Does anyone have any thoughts on this? I guess there must be a flaw in my logic somewhere but usually the only way to find it is to put it out there for public discussion.

  2. #2
    This is probably a debate best answered by students of Isaac Newton. I am more inclined to describe myself as student of Isaac Walton and so regret I can offer little in the way of answer beyond informed speculation, which is rather less than your question deserves.

    I can, however, offer this link which may go some way to explaining the transfer of energy consequent upon the impact of a projectile.

    http://www.fbi.gov/hq/lab/fsc/backis...research03.htm

  3. #3
    There are two principles of physics here... one is the conservation of energy (total energy in a discrete 'system' remains constant), and the other is Newton's 3rd law (when a force is exerted on body A by body B there is a force equal in magnitude and opposite in direction exerted on body B by body A).

    When you fire a cartridge you are converting chemical energy into heat, sound (bang!) and kinetic energy (the bullet moves). As the bullet moves through the air it loses energy to air resistance in the form of heat. When it gets to the target (i.e. a deer) the hair, skin, flesh, bone begins to exert a force upon that bullet which is equal and opposite to the force the bullet is exerting on the tissues of the deer. As the bullet continues to move against the tissues it is 'doing work', i.e. it is moving against a force. Similarly the tissues of the deer are 'doing work' on the bullet. If the sum total of this work exceeds the kinetic energy of the bullet then the bullet will not exit. If the sum total is less than the kinetic energy of the bullet then the bullet will exit with whatever kinetic energy it has left.

    As the total energy must remain constant then where has this missing kinetic energy gone? As work was done on the deer and on the bullet the kinetic energy was largely converted to heat within the deer and a bit of sound (the bullet strike).

    When we talk about 'shock' or 'hydrostatic shock' we are really talking about the way the bullet does work on the tissues of the deer. As it moves through the tissues, which are largely water and therefore almost incompressible, it displaces at very high velocity a volume of tissue all round the path of the bullet resulting in contusions, bleeding and general damage.

    So you are right so far as that some of the energy is used to deform the bullet, but some of the energy is also used to damage the tissues of the deer resulting in loss of blood pressure, nervous shock and all the other physical attributes that together constitute a quick and fatal injury. So the bullet has in fact 'dumped' it's energy within the deer (and the bullet) in the form of heat and any left over energy is what is propelling the bullet should it exit the other side.

    If you take a bullet that is said not to 'dump' it's energy, say a full metal jacket, the the principles are exactly the same, though this time the work done on both bullet and deer is less and therefore the bullet is likely to exit with a lot more leftover kinetic energy.

    Hope this makes sense!

    Alex

  4. #4
    Hi caorach
    Inertesting one this, should be good to watch the replys on this subject
    I think your point of view is very plausible and like you I’m not qualified to say anything for sure, just what I see
    However deer that drop on the spot why?,
    You hear the strike, then reaction, deer drop or run.
    For the deer that drops on the spot I suspect it must be a form of shock.
    I do think that he bullet type will have some impact with reference to the ones that give excessive meat damage, these being more likely to drop a deer with excessive shock due to the amount of damage done.
    So I can go with your point of view caorach and Im looking forward to other points of view we never stop learning.
    I was writing this post at the same time csl post a very comprensive explanation, you sometimes know when you should leave it to experts

    welldone csl its what I was trying to say i think



    Smithy
    Last edited by smithp18; 27-02-2010 at 14:32.

  5. #5
    Spectacular, Alex! Well done and much appreciated.

    Obviously Newton is your man. Walton would have gone on more about tench and chub.

  6. #6
    Thank you to everyone for their replies, the Indian paper was most interesting reading and worth a look.

    I agree with what you are saying Alex but perhaps I should highlight that my position is that almost all the energy "used" when shooting a deer goes into deforming the bullet. I believe I've presented evidence of bullet strikes where this can be seen to be the case and which demonstrate that under certain circumstances virtually all of the kinetic energy can be used to deform the bullet. I suspect that the amount of energy needed to kill a deer in terms of the work needing to be done to cut flesh, bone and vital organs is trivial compared to the amount of energy in the system and my assertion is that this energy is expended on the bullet itself. A bullet that "blows up" on a shoulder might be another good example - the energy in the system has been "used" not to kill the deer but rather to destroy the bullet.

    As I've stated previously I can see no place for "shock" or "hydrostatic shock" or other mystery forces in the reliable and effective killing of deer. Deer are killed by disrupting major organs and causing a loss of blood pressure, if some mystical shocking force was a reliable event then it would be sufficient to shoot them in the tail with a very high velocity bullet and I don't think anyone would be willing to agree to do this for a year to see how it works out. In saying that I accept, as smithp18 says, that deer do drop to the shot on occasions and this is not readily explained by my position on this matter.

    The Indian paper Iwrch linked to certainly hints at elements of what I'm saying by implying that even a bullet passing through glass can generate high temperatures and so on as a result of the deformation of the glass and the bullet.

  7. #7
    Quote Originally Posted by caorach View Post
    I agree with what you are saying Alex but perhaps I should highlight that my position is that almost all the energy "used" when shooting a deer goes into deforming the bullet. I believe I've presented evidence of bullet strikes where this can be seen to be the case and which demonstrate that under certain circumstances virtually all of the kinetic energy can be used to deform the bullet. I suspect that the amount of energy needed to kill a deer in terms of the work needing to be done to cut flesh, bone and vital organs is trivial compared to the amount of energy in the system and my assertion is that this energy is expended on the bullet itself. A bullet that "blows up" on a shoulder might be another good example - the energy in the system has been "used" not to kill the deer but rather to destroy the bullet.
    The proportion of energy divided between the bullet and the target is purely dependent on the materials involved. Your previous example of a lead bullet impacting a steel plate would be an example of where almost all the work done is by the plate upon the bullet. Conversely, shooting a bullet into a bullet recovery system 'CSI style' is an example of the exact opposite. The bullet is recovered completely intact and the energy has gone into doing work against the fibres in the recovery system.

    A deer would be somewhere in the middle of this. The exact proportion would be widely variable I'd suggest, depending on bullet type, where it hits etc, but I would propose that a good proportion of the energy goes into doing work against the organs and tissues.


    As I've stated previously I can see no place for "shock" or "hydrostatic shock" or other mystery forces in the reliable and effective killing of deer. Deer are killed by disrupting major organs and causing a loss of blood pressure, if some mystical shocking force was a reliable event then it would be sufficient to shoot them in the tail with a very high velocity bullet and I don't think anyone would be willing to agree to do this for a year to see how it works out.
    I don't believe in a mystical 'shock' force either but what I was attempting to explain with regard to hydrostatic shock was that this is the mechanism by which a bullet damages tissues in the volume surrounding it's path. i.e. if you got a flattened bullet and pushed it through by hand on the end of a stick you would not see the same level of contusions and damage to the surrounding tissues you would see with a bullet travelling at it's normal speed. Another example is that a bullet passing in the vicinity of the spine can impart enough energy to the spinal chord to cause temporary or permanent paralysis without actually directly contacting the nerve. It is pushing tissues aside that in turn push upon other tissues at such a high velocity that trauma occurs. This is where the energy is expended and this, to me, is effect we call 'hydrostatic shock'.

    I think you are referring to the old 'a bullet sends a shockwave around the whole vascular system' theory... I too would probably tend towards categorising that more towards anecdotal than factual, personally.


    regards,

    Alex

  8. #8
    Alex, that was an outstanding explanation & Iwrch; very very funny (Walton)......
    Last edited by Sariel; 27-02-2010 at 17:53.

  9. #9
    Not an expert on this, to scientific for me, but this is the reason that bow hunting is not allowed in this country an arrow has little or no shock power only penetration, hence hunting arrows have very sharp bladed tips so that they cut artery's and veins a animal shot with a bow, in reality bleeds to death, now for example a deer grazed across the back and I mean grazed no actual penetration will drop to the ground immediately, often getting up at once sometimes laying down for as long as a minute
    before getting up and running off, now this is from a bullet that has not entered the animal, I would think that a direct hit is like being hit by a truck. Sure someone with more scientific knowledge will be able to explain it better.

  10. #10
    Quote Originally Posted by csl View Post
    I would propose that a good proportion of the energy goes into doing work against the organs and tissues.
    I have no science to support my position but the best I can say is that I have a feeling that more energy than we suspect is actually used up deforming the bullet. I really don't see that it takes you to do much work to put a hole in a deer and its organs. However, as you point out it would be difficult to determine where the bullet is working against the organs and where the organs are working against the bullet

    There is probably no chance of me ever getting a clear answer to this and we also have the situation that Griff and others are discussing on another thread of bullets passing clean through and retaining a lot of energy.However, I find it useful to consider this sort of thing as sometimes stuff that I believe to be true turns out to be utter rubbish and often a bit of thought would have revealed the holes in the logic.

    I am afraid Bogtrotter that I don't agree with your position. I don't dispute that deer occasionally fall over very rapidly, though I might question if they fall over with only a slight graze to the back that didn't hit the "fins" on the spine, but I don't believe that "shock" as you see it is a reliable or useful mechanism by which to kill a deer. As stated previously if this "shock" mechanism was as effective as some might maintain then we would be quite happy to shoot deer in the tail, or ear, with a 22-250. The fact that we take carefully aimed shots at the heart/lungs, spine or brain indicates to me that even people who might claim to believe in the magical shocking effect of fast bullets don't have much faith their belief. However, I must highlight that my position is based on "belief" rather than "science" and so might be totally wrong but to date I've seen no science to indicate it is incorrect.

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