Any military guys out there, or just people who know about firearms, I could use your expertise for this.

A friend of mine and I were recently talking about what makes the "crack" you hear when a gun is fired; he says it's the gunpowder exploding when the hammer strikes the bullet, I say it's the sonic boom from the bullet tearing through the air at supersonic speeds.

Am I right? Is he right? Are we both right (or, conversely, wrong)? Thanks for your input.

Sonic boom.

No expertise, just is the sonic boom.

Gunners Mate 2nd class in the USCG for 5 yrs. both are right. There is a crack and then a boom. Crack is the primer and the powder the boom is the projectile leaving the muzzle. I think.

The loud boom is the explosion caused by compressed gases being released. A black powder guns ball does not by any stretch break the sound barrier and there is the same loud boom.



Enjoy.


USMC 4 years, Cop 5 years, redneck gun nut 28 years.:D

Depends on the distance at which one is hearing the crack. When you are firing, you will hear the powder burn/gas expansion as it leaves the barrel. At longer ranges, the crack sound is the projectile breaking the sound barrier.


Former USMC and addicted hunting nut. :-)

Punchingdummy is correct.

breaking the sound barrier. So a bullet accelerates after you fire it?

It's the powder, aside from the black powder rifles a standard .45 round is also subsonic. But it's not quiet when you fire it. Tell him to set off a firecracker sometime, then ask if it's breaking the sound barrier or not. It still makes a big noise.

Originally posted by Akurra
breaking the sound barrier. So a bullet accelerates after you fire it?

No.

I've fired an M1 with a silencer. There was no initial pow, but you could still hear the bullet crack as it broke the sound barrier. Punchingdummy is completely correct. Quick Clavenism: silencers work by trapping the gas of the explosion of the gun powder, and reduce muzzle vibration. Because it traps the gas, it doesn't allow for gas operated automatics and semi-automatics to rechamber .. so whenever you see a guy in the movies firing a machine gun with a silencer, it's bullshit. In addition a revolver has an opening between the trigger and chamber, which allows gas to escape. So while yes, a silencer would reduce the sound, it's far from "silent".

^^= WRONG

CaptShady, think about what you are saying. The M1 you fired is gas operated. A silencer should have no effect on a gas operated gun, the gas having already chambered the next rond by the time it enters the silencer. Machine guns can and do work with a silencer quite well, most are blowback action, but being automatic has nothing to do with it. Also, reducing muzzle vibration has nothing to do with making a gun quiter. It may make the gun more accurate, but does not reduce the noise level.
The noise you are hearing depends on the type or gun being fired. If its a muzzle loader or black powder gun, its the primer that "cracks" and the explosion of the powder a split second later is the "bang". A subsonic round, <=1000 feet per second, produces only the "bang" from the exploding powder when the bullit leaves the gun. All other rounds, see Punchingdummy's post.

The M1 I fired was bolt action, noit semi-auto. As for the rest .. I'm definitely no expert, but that's how it was explained to me. I hate it when ya think you know something and find out it's bunk.

Sorry Captain. I thought you were talking about the M1 carbine or M1 Garand, both of which are gas operated. Yeah, there is tons of bad information out on guns, sounds like you got alittle. :) Your other parts were correct though. Here is a cool site if someone wants to read-up on guns.

http://world.guns.ru/shotgun/sh10-e.htm

Use the pull-down menu in the upper, left corner to select the type of gun you want.

Originally posted by Akurra
breaking the sound barrier. So a bullet accelerates after you fire it?

The bullet is only accelerating as it is traveling down the barrel in front of the expanding gas. Once it leaves the barrel it is not accelerating. This is why guns with longer barrels have higher velocities than guns with shorter barrels: By keeping the barrel long you keep the bullet in front of the expanding gas longer and get more acceleration.

Crack of the gun.

Several people already chimed in so I'll give my .02 as well. My understanding is that it is due to the rapidly expanding gases of the gun hitting the relatively still air outside the barrel that causes the noise.

For supersonic rounds you'll hear two cracks depending on how far you are. One is the report of the gun being fired, the other is the sonic boom of the round.

^^ correct.

a good analogy for the muzzle blast is the *pop* a champagne cork makes when it leaves the bottle. Same principle: compressed gas is released rapidly into the atmosphere. A silencer eases the transition, thus muting the muzzle blast.

Both sounds make me dive for cover.