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Black Angus McPherson

Sound Barrier vs. Silencer Question

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A hyper-sonic bullet breaks the sound barrier and makes a boom when it leaves the barrel. I got that. A hyper-sonic bullet breaks the sound barrier and makes a boom when it leaves a silenced barrel. The silencer only reduces the sound of the explosion. (ok, it ain't really an explosion, just follow me here.) I think I got that, too.

 

But, if a hyper-sonic bullet goes thru a silencer with a really large "can" why isn't the sonic boom "silenced" inside the can? Does the sonic boom follow the bullet until it slows to below the speed of sound? If so, why don't we hear the boom throughout the flight of the bullet, kind of like a really loud train instead of the one loud crack we hear upon firing?

 

If I'm 1000 yards away from where the bullet is fired and I have no way to hear the gunshot, will I hear the crack of the sonic boom as a hyper-sonic bullet passes me? If so, why don't I hear it booming on down the range past me like the earlier mentioned really loud train?

I understand I wouldn't hear it coming, it being faster than the speed of the sound, and all.

 

Just wondering.

 

Angus

 

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At 600 yards a bullet snaps like a whip when it passes overhead. Loud enough that you should wear ear protection. Never heard one before it got there.

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Yes, if you are down range and a bullet passes over your head, it creates a distinctive "CRACK!" that is its sonic "boom".

 

Most of the noise you hear from the muzzle is actually caused by expanding gases suddenly being released into the atmosphere. Remember, a sound wave is fundamentally a pressure wave that propagates through air. The gunpowder gases are at very high pressure, and they create a large pressure wave that propagates all the way to your ear.

 

Suppressors are effective because they reduce the pressure at which the gases of gunpowder combustion reach the atmosphere. Lower pressure when reaching the atmosphere leads directly to lower pressure wave and lower audible sound levels.

 

I used to do a lot of NRA and military high power matches where we tended targets at ranges from 200-1000 yards. Scorers stood behind a large berm and targets slid on a frame that came down to us for scoring, but then were pushed back above the berm to be seen and shot at from the firing line. It was very disconcerting the first time I heard the sonic crack come overhead, and then a second or two later hear the low "boom" of the muzzle blast.

 

Charlie describes it well when he says it sounds like a whip snap.

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Think of a sonic boom like the wake a boat makes as it moves across the water. The wake only passes you once. Not continuously.

 

Here's what happens during a sonic boom

 

You can actually see the shock wave using Schlieren imaging. Google it to see some really cool photos.

 

Sonic booms and Mach cones

bullet-mach-cone.jpg

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I've pondered on that too black angus. I decided that the sonic boom followed the bullet the entire length of it's hypersonic travel. From the other responses here, I guess I had that figured right. The main reason I decided on that is that I knew you could hear that sonic boom under the right conditions. When out hunting, if someone takes a long shot with a high powered rifle, or makes a clean miss, I can hear the bullet make quite a distinctive whine. On the long distance shots that hit, it has a whine and then suddenly stops. On misses it just fades away. Of course, you can't really hear this when you're right behind the gun though, I think you have to be off to the side of the bullet's path. At least that's what I tell myself so I can believe my friends aren't shooting at me. Anyway, to answer the question I think you asked, I don't believe a silencer can do anything about that sonic boom. If it does, then it only helps right at the muzzle. The point of a silencer is to reduce the noise by xdB, that's why they are more accurately called suppressors.

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Yes, if you are down range and a bullet passes over your head, it creates a distinctive "CRACK!" that is its sonic "boom".

 

Most of the noise you hear from the muzzle is actually caused by expanding gases suddenly being released into the atmosphere. Remember, a sound wave is fundamentally a pressure wave that propagates through air. The gunpowder gases are at very high pressure, and they create a large pressure wave that propagates all the way to your ear.

 

Suppressors are effective because they reduce the pressure at which the gases of gunpowder combustion reach the atmosphere. Lower pressure when reaching the atmosphere leads directly to lower pressure wave and lower audible sound levels.

 

I used to do a lot of NRA and military high power matches where we tended targets at ranges from 200-1000 yards. Scorers stood behind a large berm and targets slid on a frame that came down to us for scoring, but then were pushed back above the berm to be seen and shot at from the firing line. It was very disconcerting the first time I heard the sonic crack come overhead, and then a second or two later hear the low "boom" of the muzzle blast.

 

Charlie describes it well when he says it sounds like a whip snap.

 

+1 - it really is a sharp crack - you Have to use ear protection or end up like me - deaf as a rock. I used to pull targets for the NRA matches in Illinois. OUCH!

 

STL Suomi

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One plus of suppressors from a tactical standpoint is that even though the bad guys that aren't hit can hear the supersonic sound of the bullet passing by, because the initial sound of the round being fired is suppressed enough it is not possible to determine the origin direction of the shot. The systems used to determine where a shot is fired from use the different times it takes for the bullet to pass the microphone array and the sound of the round being fired to arrive.

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A bullet from an AK47 makes a distinct crack that I likened to a sharp finger snap as it goes past an O1A at about 3000 feet.

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with the sonic crack is that enough to tell you where the point of orgin started from?

NO. Just get some cover and look for muzzle flashes, You m\ight get lucky.

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I use a suppressor on my ar15 in 300 black out. When I use subsonic ammo such as a 220 grain bullet, it is very quiet. Switch to a 120 grain supersonic, it is quieter, butt you get that crack from the sonic boom.

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First round pop.

 

When you fire the first shot, dry, the oxygen in the barrel gives you that nice BANG. The next shot, the barrel is full of powder gas - no oxygen, so pow instead of BANG.

 

Shooting my Ruger, it goes BANG pow pow pow pow pow pow pow pow pow.

 

Slide locks back, and in the time it takes to reload the mag, the barrel airs out, and is now full of oxygen again, and it's BANG pow pow pow etc.

 

With a wet can, it's full of liquid, so no oxygen, so no "first round POP".

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with the sonic crack is that enough to tell you where the point of orgin started from?

As was said, no but it gets even better. Since most people don't understand how sound waves work you'll get them swearing up and down that the shot came from THAT way when in reality, THAT way was just the closest solid object for the sound waves to bounce off of.

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By the way when you are pulling targets in the pits for a black powder cartridge rifle at 600 yards things are different. You will hear the boom of the rifle and then the sound of the lead bullet

slapping the target. You do not need to wear ear protection for that. You can sit and day dream and then when you hear the boom have time to look up at the target and see the bullet hit.

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Think of a sonic boom like the wake a boat makes as it moves across the water. The wake only passes you once. Not continuously.

 

Here's what happens during a sonic boom

 

You can actually see the shock wave using Schlieren imaging. Google it to see some really cool photos.

 

Sonic booms and Mach cones

bullet-mach-cone.jpg

 

GREAT description. I have a basic knowledge of how a "suppressor" works. I thought the sonic boom followed the bullet but I didn't understand why the "boom" didn't just approach and pass like a train. Wouldn't it suck if that were true? The analogy comparing the sonic boom to the wake of a passing boat makes perfect sense to me.

 

Way back in the day when jets were still allowed to break the sound barrier over populated areas I always thought that it was just the area around our house that was subject to the window rattling boom.

 

I feel much smarter now. Youse guyz is jeniuses.

 

Thanks all,

 

Angus

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The 'crack' comes from where the bullet is. A suppressor serves to reduce the muzzle blast of the firearm and at distance, makes it more difficult to tell where the shot came from.If the bullet is traveling at 2,000-3,000fps you'll hear the crack AFTER it hits ya......

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