Quantcast
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

If high speed bullets carry a destructive shock wave, why no paper target damage?

Discussion in 'General Gun Discussions' started by The Real Hawkeye, Oct 10, 2005.

Thread Status:
Not open for further replies.
  1. The Real Hawkeye

    The Real Hawkeye member

    Joined:
    Jan 31, 2004
    Messages:
    4,238
    Location:
    Florida, CSA
    We often hear of the destructive shock wave that travels with high speed bullets, but if this shock wave is so destructive to living tissue, why doesn't it cause paper targets to blow up?
     
  2. Amish_Bill

    Amish_Bill Member

    Joined:
    Nov 29, 2003
    Messages:
    1,543
    Location:
    atl ga
    Ummm.... maybe 'cuz the paper of the target is only a zillionth of an inch thick?
     
  3. Coltdriver

    Coltdriver Member

    Joined:
    Dec 26, 2002
    Messages:
    2,202
    Location:
    Colorado
    The "shock wave" effect you are referring to comes from the rapid displacement of tissue.
     
  4. RyanM

    RyanM Member

    Joined:
    Jan 4, 2005
    Messages:
    4,412
    Location:
    PA
    The only real "shock wave" caused by a bullet impact doesn't do squat, anyway. A lithoriptor (kidney stone treatment thingie) generates shockwaves in your body upt 5 times as strong as those caused by a bullet, up to 2,000 times in one therapy session, with zero damage (except to the kidney stones).

    There is some displacement of tissue due to the outward transfer of momentum, which can cause some tissue damage if it's displaced far enough. Partial fragmentation of the round helps, too. But it's not a "shock wave" anymore than a splash in water is a "shock wave."

    If you want to see temporary cavitation work on paper (paper is inelastic, so it becomes a permanent cavity and you get a way bigger hole than with people), try shooting a phone book that's been soaked in water.
     
  5. Majic

    Majic Member

    Joined:
    May 3, 2003
    Messages:
    5,370
    Location:
    Virginia
    Paper has very little water content. The shock referral of a bullet is a function of hydraulics.
     
  6. Lone_Gunman

    Lone_Gunman Member

    Joined:
    Dec 24, 2002
    Messages:
    8,056
    Location:
    United Socialist States of Obama
    I don't think I have heard the term "shock referral". To what does that refer?
     
  7. Gifted

    Gifted Member

    Joined:
    Jul 28, 2004
    Messages:
    1,009
    Location:
    Missouri
    So, what affect does a shockwave have on the ear? I've heard all that BS about shooting a .50 between two people, but it's gotta at least thump your eardrums if it's close enough.
     
  8. Kurush

    Kurush Member

    Joined:
    Jul 16, 2005
    Messages:
    1,078
    Supersonic bullets do make a shock wave--a sonic boom that is--but it isn't going to kill anyone just by passing near them. What kills people in explosions is heat and pressure waves, and bullets have very little heat in them, and they only displace the air that's immediately in front of them. So any pressure wave from a .50 BMG isn't going to kill anything bigger than a mosquito.

    EDIT: I read some of the other responses, are we talking about shock waves in air or in the target? There are no shock waves in the target, Fackler said that tissue recoils (as a rule of thumb) at 1/5th the speed of the bullet which for any real world bullet is subsonic.

    Also, water doesn't have shock waves at any speed, it's an incompressible fluid.
     
  9. Medusa

    Medusa Member

    Joined:
    Jul 20, 2005
    Messages:
    942
    Location:
    EE, Europe
    There can be pressure waves in water, it is NEARLY incompressible. When you hit the water right above the fish with a paddle then the fish dies due the increased pressure at it's depth (of course, if it is shallow enough, say couple of yards). The pressure divides in liquid equally in all directions.
     
  10. Kurush

    Kurush Member

    Joined:
    Jul 16, 2005
    Messages:
    1,078
    It's incompressible for all practical purposes. But you seem to have misunderstood me, I said shock waves are impossible in water, not pressure waves. A shock wave is a special kind of pressure wave that forms when an object passes through a compressible fluid at supersonic speeds.

    If you've ever seen film of a bomb hitting the ground, that white film that spreads away from the blast for ~50 feet or so then disappears is a shock wave. Also when soldiers hear a "snap" (rather than a "whiz") from a bullet passing nearby their ears were inside its (relatively weak) shock wave.
     
  11. Medusa

    Medusa Member

    Joined:
    Jul 20, 2005
    Messages:
    942
    Location:
    EE, Europe
    I know the difference between the 2, sorry about it, as am active in material sciences ;) But sometimes the difference between the 2 is quite vague.
     
  12. EddieCoyle

    EddieCoyle Member

    Joined:
    Sep 17, 2005
    Messages:
    1,231
    Location:
    Massachusetts
    Because it's the wrong target to demonstrate it

    Instead of a paper target, shoot a gallon jug full of water and you'll get an imperfect demonstration of what happens to living tissue (which is mostly water).
     
  13. Medusa

    Medusa Member

    Joined:
    Jul 20, 2005
    Messages:
    942
    Location:
    EE, Europe
  14. The Real Hawkeye

    The Real Hawkeye member

    Joined:
    Jan 31, 2004
    Messages:
    4,238
    Location:
    Florida, CSA
    I've shot lots of potatos with .22 caliber pellet rifles and have seen them splatter pretty good from a solid hit. Since these pellets do not exceed the speed of sound, I assume it is something other than a shock wave that causes this effect. Comments?
     
  15. Justin

    Justin Moderator Emeritus

    Joined:
    Dec 29, 2002
    Messages:
    19,285
    Location:
    THE CHAIR IS AGAINST THE WALL
    Supersonic bullets create enough sound to cause hearing loss. If you ever pull pits in a High Power match, they make you wear hearing protection.

    A .223 zinging overhead sounds roughly about as loud as a .22 pistol being fired.
     
  16. Kurush

    Kurush Member

    Joined:
    Jul 16, 2005
    Messages:
    1,078
    The flesh of the potato resists the passage of the bullet much more than air does, which slows the bullet down. Since momentum is conserved (Newton's laws...), the potato recoils in the opposite direction of the force it was exerting. The momentum of the potato flesh is greater than the strength of the bonds holding the potato in its normal shape, so the potato flies apart.

    Cool. I'm a math student and I've worked on several research grants doing nonlinear materials simulation. There is definitely a lot of confusion out there about shock waves vs. pressure waves.

    I think there would be a lot less confusion about this sort of thing if more people understood pressure waves vs. shock waves. So here's my humble attempt:

    Shock waves, in ballistics, are only going to occur in the air, so there is really no point in talking about them except in relation to ear protection.

    A shock wave is what happens when a fluid is being pushed faster than it can get out of the way (it can normally only move at the mach 1 by definition). Since the fluid can't get out of the way, it compresses into a very thin, very hot super compressed membrane. This is the film around the bombs I mentioned before.

    As I mentioned, water is incompressible so it can't have shock waves; if you try to pass through water at > mach 1, it will just become very stiff and the object will either bounce off or be smashed. Also, mach 1 in water is ~4500 fps so we normally don't have to worry about it.

    Gel/meat is compressible, and it's sort-of fluid like but (1) its speed of sound is even higher than water and (2) any shock wave is going to exhaust itself almost instantly by heating and stretching the nearby gel/meat and dissipate. Also, as I mentioned before in real tests gel/meat recoils away from a bullet at 1/5th of the speed of the bullet, so unless this is 2050 and we're shooting portable railguns or something at 20000 fps it doesn't enter into it.
     
  17. thorn726

    thorn726 Member

    Joined:
    Dec 15, 2004
    Messages:
    1,388
    Location:
    berkeley, CA
    i'll venture it's about the same as conduction- the wave needs something to travel thru
     
  18. brickeyee

    brickeyee Member

    Joined:
    Feb 25, 2005
    Messages:
    3,135
    If you ever gat a chance to 'play' with real explosives you can generate shock waves in water, even in steel and concrete. They are typically accompanied by fracturing of the material. Sometimes in predictable ways, sometimes not.
    In terms of terminal ballistic behavior both momentum and energy come into play in any materials reaction to impact. The material properties determine what will happen, and due to the forces involved many things do not respond in an obvious manner. Notice in the picture of the apple being struck that material is ejected backwards relative to the impact.
     
  19. ZenMasterJG

    ZenMasterJG Member

    Joined:
    May 20, 2005
    Messages:
    237
    Location:
    Hiding between server racks, quietly sobbing.
    This is just an energy thing.
    The kinetic energy of a projectile is equal to half the mass of the projectile times the square of its velocity. (KE=1/2m*v^2)
    When the pellet hits the potato, most of this energy is lost. (The pellet may go straight through and keep going, in which case it retains some of its kinetic energy.) Energy is conserved, that is, it doesnt just disappear. When the pellet puts its energy into the potato, its is dispersed as a little bit of heat, and a bunch of potato explode-y.

    And yes, "Potato explode-y" is a scientific term.

    Edit: sorry Kurush! Didn't see your explaination, which is better and more accurate then mine. The only problem with yours is you failed to use the phrase "Potato explode-y"
     
  20. Kurush

    Kurush Member

    Joined:
    Jul 16, 2005
    Messages:
    1,078
    You can generate very strong pressure waves, you can't generate any shock waves.

    Here's a table I got off the web:
    Code:
    temp F(C) 0 atm  500 a   1000 a  2000 a    3000 a
    68 (20)     1.0016 0.9804 0.9619  0.9312    0.9065 
    So at 500 atm, (7,348 psi) water compresses about 2%
    At 3000 atm, (44,088 psi) water compresses only 10%

    In a shock wave, density inside the wave is typically triple the normal density. How much pressure would have to be applied to cause water to compress by 66%? (we'll be generous and ignore the change in temperature, which makes water even harder to compress)

    Using least squares, we get a function approximating the pressure data above:
    Code:
    0.99713 - 0.0000314*x
    Solving that for .33 we get about 21000 atm (a whopping 308,614 pounds per square inch)

    A direct hit from a nuclear bomb only creates about 5000 psi of pressure.

    So I think it's safe to say that high explosives do not cause shock waves in water, they cause pressure waves.
     
  21. silverlance

    silverlance Member

    Joined:
    Jul 11, 2005
    Messages:
    2,142
    Location:
    In my Foxhole
    hm my .02

    i've heard of horrible stories of idiots firing their glocks underwater and the pressure waves really f**** up their internal organs as a result.

    this last one i heard of was some guy jumping into the deep end of his swimming pool and firing it at 10ft like a chlorinated navy seal...
     
  22. RyanM

    RyanM Member

    Joined:
    Jan 4, 2005
    Messages:
    4,412
    Location:
    PA
    Those "firing a gun underwater overpressure" stories are complete, utter, 100% bunk. Ask any diver who's used a "bangstick" what it's like. Muffled thump, dead fish. Even in a small cave, just a muffled thump.

    They can stun or kill a small fish if fired against a cave wall about a foot away from the fish, though. Mostly because the wall then projects the pressure wave straight backwards, towards the shooter, so it hits the fish at slightly reduced strength. And it still just sounds like a thump.

    It's like trying to claim that the cylinder gap blast from a revolver will split someone's head in half if they stand too close to you at the firing line. The blast is definitely capable of taking a finger off if it's right up against the cylinder, but the danger level drops off pretty quickly with distance...
     
  23. chris in va

    chris in va Member

    Joined:
    Mar 4, 2005
    Messages:
    6,097
    Location:
    Louisville KY
    All the scientists came out for this one. :rolleyes:
     
  24. Medusa

    Medusa Member

    Joined:
    Jul 20, 2005
    Messages:
    942
    Location:
    EE, Europe
    Whaddaya expect from such a headline? :neener:
     
  25. c_yeager

    c_yeager Member

    Joined:
    Mar 14, 2003
    Messages:
    5,479
    Location:
    Seattle
    "Destructive Shockwave" :scrutiny:
     
Thread Status:
Not open for further replies.

Share This Page