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Explosion force inside gun barrel

  1. Jul 18, 2014 #1
    When I fire a gun there is an explosion inside a barrel that causes bullet to fly and gun to recoil but when a barrel is blocked a whole gun can explode, does it mean explosion inside barrel is stronger in second case?(The reason why I am wondering about it is because forces of explosion press against barrel in both cases but in the first case the barrel is not destroyed)
     
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  3. Jul 18, 2014 #2

    phinds

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    Because when the bullet leaves the gun barrel, so does the pressure. If you blocked up the end and the barrel exploded, there would be no recoil either, for the same reason. It is the expanding gasses leaving the end of the barrel that causes the recoil.
     
  4. Jul 18, 2014 #3
    So does it mean the pressure inside barrel is higher if the barrel is blocked ( pressing with more force at the barrel causing it to explode)?
     
  5. Jul 18, 2014 #4

    A.T.

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    Will the blocked barrel explode, if there is no projectile just the explosion?
     
  6. Jul 18, 2014 #5

    phinds

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    No, it means exactly what I said it means ... that the pressure is ejecting the projectile and if there is no projectile but the barrel is blocked then the barrel will explode.

    What would you expect to happen if the gunpowder goes off but if, as A.T. asked, there is no bullet in the barrel.
     
  7. Jul 18, 2014 #6
    But if the expanding gasses can go off when the barrel is open and can't go off if the the barrel is blocked shouldn't it mean the pressure is bigger or at least works for a longer time when the barrel is blocked (cause gasses have nowhere to go) ?
     
  8. Jul 18, 2014 #7

    Drakkith

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    I don't know about the pressure being larger, but it is definitely applied to the gun for a longer period of time since it can't get out unless the gun ruptures.
     
  9. Jul 18, 2014 #8

    SteamKing

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    I think what happens in the case of the blocked barrel, is that the powder doesn't combust all at once.

    When the trigger lands on the primer cap, the powder starts to burn, increasing the pressure in the barrel. While the bullet moves down the barrel, the powder is still burning, and normally, if one plotted the pressure in the barrel versus the distance traveled by the bullet in the bore, there would be a rapid rise in pressure until the bullet starts to move, the pressure peaks, and then decreases smoothly the further the bullet travels in the barrel before leaving the muzzle.

    If the bullet is stopped before it can exit the muzzle, the powder is still burning behind it, but because the gun is now jammed, the pressure continues to rise, rather than fall. Once the pressure exceeds a certain value, some part of the gun will fail due to the high pressure which can't escape.

    The study of what happens inside the gun when it is fired is called 'interior ballistics', as opposed to 'exterior ballistics', which is the study of the projectile once it has left the muzzle.

    http://www.frfrogspad.com/intballi.htm

    The section entitled 'Bang!' has a sample graph like the one described above showing how the pressure inside the barrel varies.
     
  10. Jul 18, 2014 #9

    A.T.

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    So the barrel would also explode if there was no projectile, just a blank fired in a blocked barrel?
     
    Last edited: Jul 18, 2014
  11. Jul 18, 2014 #10

    SteamKing

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    A blocked barrel is not the normal state of affairs for firing a gun. If something doesn't come out the end of the barrel when the gun is fired, it's liable to come out on the other end facing the holder of the weapon.
     
  12. Jul 18, 2014 #11

    Chronos

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    An explosive charge detonated within a closed cylinder is also known as a pipe bomb.
     
  13. Jul 18, 2014 #12
    The bullet with its momentum and kinetic energy, will destroy whats blocking the barrel and possibly part or whole of the barrel with it. If there is no bullet then the explosion gases will still have a total energy equal or slightly greater than the kinetic energy of the bullet , but because this energy will be randomly distributed among the molecules of the gases the barrel may hold against the explosion.
     
  14. Jul 19, 2014 #13

    CWatters

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    Aside: I believe there would be a recoil on a blocked gun. I'm pretty sure the bullet will move (if not very far).
     
  15. Jul 19, 2014 #14

    A.T.

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    A pipe bomb is designed to burst. I asked about a normal barrel, designed to withstand the explosion while a projectile still blocks the exit during its acceleration. If you take this normal barrel and seal the exit, will a blank cartridge (same amount of explosives as a normal cartridge ) burst the barrel?

    That is what I was getting at. Is it the pressure of the gases that bursts a barrel blocked at the exit. Or is it the energy stored in the projectile, released in a concentrated manner when it hits the obstacle.
     
  16. Jul 19, 2014 #15

    Chronos

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    A blocked gun barrel is entirely capable of rupturing due to the force of expanding gasses with no escape path.
     
  17. Jul 19, 2014 #16

    A.T.

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    Sure, you can make anything burst in general. But my question is more specific:
    - The barrel is blocked at the very end, so the gases can take up the whole barrel volume.
    - The amout of gun powder is the same as in a normal shot, just no projectile.
     
  18. Jul 19, 2014 #17

    SteamKing

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    IDK if anyone can answer this question except in specific cases; there are too many variables to consider otherwise. The design of firearms is too varied to make a blanket pronouncement on the matter. All that one can say is that firing a weapon with a blocked barrel is a highly dangerous situation.
     
  19. Jul 21, 2014 #18
    Actually there is indeed a difference between the manner in which the burning/explosion propagates in the two proposed scenarios, because burning/explosions change as a function of pressure, among other things.

    In the case of a normal, commercial cartridge, there is a pre-defined pressure requirement to begin moving the bullet from the resistance of the friction hold of the cartridge. As the bullet begins to move into the barrel the volume into which the explosion is expanding is increasing and temperatures begin to drop depending on complex interaction of explosive material impulse, bullet mass, friction within the barrel, etc.

    Consider that a cartridge held in a vise (extremely dangerous!) where there is no barrel and where the explosion propagates into atmospheric pressure and there is no resistance aside from aerodynamic to the movement of the bullet, behaves very differently from that of being enclosed in a barrel, or underwater. etc.

    The final scenario in which the end of the barrel is blocked and a blank cartridge employed, will have very different (non-linear) effects from any other environmental scenario in which temperature and pressure are major players.
     
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