# Physics Question - Bullet in Barrel

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

1. ### 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. ### Mass10mmArmed 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

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Exactly. Well said

4. ### 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 RuleSenior 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.

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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

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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

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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. ### samurairabbiDungeon 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_minnSilver MemberMillennium 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

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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 WarriorAm Yisrael ChaiCLM

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Yes.

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

13. ### countrygun

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Taco Bell sells bullets?

14. ### 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

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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

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The speed of sound isn't absolute.

17. ### arclight610

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

18. ### samurairabbiDungeon 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.

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

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