Physics Question - Bullet in Barrel

Discussion in 'The Okie Corral' started by arclight610, Feb 8, 2013.

  1. arclight610

    arclight610

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    Something I've been thinking about. Is it even possible for a bullet to break the sound barrier while it is still inside the barrel of a gun?
     
  2. Mass10mm

    Mass10mm Armed Yankee

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    Not only possible, but nearly always so. How much would you expect a bullet to accelerate AFTER it leaves the barrel of a gun? Pretty much the fastest velocity a bullet has is at the moment it leaves the end of the barrel. If the bullet is going, for instance, 1,000 mph (Mach 1.3) as a muzzle velocity, it exceeded the speed of sound (Mach 1) while accelerating in the barrel.
     

  3. countrygun

    countrygun

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    Exactly. Well said
     
  4. arclight610

    arclight610

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    In order for the bullet to break the sound barrier, it has to be traveling faster than the wavefront in the medium that it creates. In a gun barrel, the bullet obturates, creating a gas tight seal (or at least nearly so). If air can't escape past the front of the bullet, the bullet can't technically exceed the wave front until it finally gets to the muzzle.
     
    Last edited: Feb 8, 2013
  5. G36's Rule

    G36's Rule Senior Member

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    Jibber jabber!

    As already stated, the highest velocity is at the muzzle. After that nothing is pushing on the bullet.
     
  6. Adjuster

    Adjuster

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    Interesting, way above my head but I see what he is saying about the bullet has to pass thru the wave in front of it to break the barrier. If the bullet can't get past the wave in the barrel how can it break the barrier while still in the barrel?


    /
     
  7. countrygun

    countrygun

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    Wrong. In order to generate a "Sonic Boom" it has to pass through that barrier, which doesn't exist inside the barrel.
     
  8. CAcop

    CAcop

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    How about adding this to the debate. Ever notice in some slo mo vids there is gas escaping before the bullet? The gas is going even faster than the bullet. Is the sound barrier being broken from behind?
     
  9. samurairabbi

    samurairabbi Dungeon Schmuck

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    Maybe the gremlins give the bullet a shove to break the sound barrier before the rifling-induced bullet rotation spins them off.
     
  10. larry_minn

    larry_minn Silver Member Millennium Member

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    The bullet can exceed the speed of sound. Even while still in mag. :0 (If the mag is in jet fighters pilots survival kit while pilot is going mach+)

    Or the plane is on a treadmill....
     
  11. arclight610

    arclight610

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    That is what I'm trying to say.

    That gas is probably the air column in the barrel getting rapidly compressed by the bullet and ejected ahead of it. That is why you can put a piece of tape on the front of your muzzle to keep mud and rain out without it affecting your accuracy. The air column will blow through the tape before the bullet ever reaches it.
     
  12. Peace Warrior

    Peace Warrior Am Yisrael Chai CLM

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    Yes.


    (The plane on a conveyor belt was more interesting thread.)
     
  13. countrygun

    countrygun

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    Taco Bell sells bullets?
     
  14. PhantomF4E

    PhantomF4E

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    The speed of sound is 1129 fps at sea level, at 70 degrees. If you fire a projectile with that same criteria "anywhere" that exceeds that speed, it is by default exceeding the speed of sound . Now do you get an audible sonic crack from within the barrel as the projectile accelerates past 1129 fps ? That may be a different story . But the "speed" of sound , is just that , speed. So I really don't get the point .
     
  15. Batesmotel

    Batesmotel

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    I am amazed at how many shooters believe that the bullet keeps accelerating well after it exits the muzzle. And that if fired from a perfectly level bore it will begin to climb.
     
  16. arclight610

    arclight610

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    The speed of sound isn't absolute.
     
  17. arclight610

    arclight610

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    [​IMG]

    Here is what I'm thinking, but in paint form.
     
  18. samurairabbi

    samurairabbi Dungeon Schmuck

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    The bullet pushes the air in front of it, accelerating the air particles beyond the velocity they would achieve propogating on their own. That "pressure wave" is not an invulnerable barrier.
     
  19. Rabbi

    Rabbi The Bombdiggity Lifetime Member

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    It doesnt work that way. The speed of sound is relative to the medium.
     
  20. Bushflyr

    Bushflyr ʇno uıƃuɐɥ ʇsnɾ Millennium Member

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    Of course the increased density of the air in front of the bullet would correspondingly increase the speed of sound. So even though the bullet is traveling at, say 1000fps, it could very well still be subsonic until it exits the barrel and the pressure drop allows the speed of sound to drop back below 1000fps.