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Old February 27, 2015, 05:43 PM   #1
Pogybait
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Bang

Many years ago, someone told me the noise you hear after a lightning bolt goes off, is not the actual lightning but rather, the air rushing into the vacuum created by the lightning. I believe this is called, thunder.

Keeping this in mind, how much of the report, bang, boom, loud noise we hear when we pull the trigger is created by the air rushing back into the barrel. There must be some sort of vacuum created when bullets exit a barrel at high speeds. It's kinda like making a popping sound by placing your thumb in your mouth and, well, you get the idea.
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Old February 27, 2015, 05:51 PM   #2
StripesDude
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Take a primed piece of brass, turn it upside down, and hit the primer with a hammer and punch. It's as loud as a gun shot. So I assume most of the "bang" is the primer going off.
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Old February 27, 2015, 05:59 PM   #3
Pogybait
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I'm sure some of the bang is attributable to the primer and powder.
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Old February 27, 2015, 06:02 PM   #4
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Apples and oranges
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Old February 27, 2015, 06:16 PM   #5
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Not to mention the difference between a .22 short and a .22 Long Rifle's report due to the speed of sound.
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Old February 27, 2015, 06:24 PM   #6
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Read post #33
http://thefiringline.com/forums/show...=559475&page=2
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Old February 27, 2015, 06:30 PM   #7
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Not to be a safety nazi but I would avoid the hammer and punch trick. Tried it as a kid and picked a lot of small bits and pieces of primer cup and anvil out of my bleeding finger.

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Old February 27, 2015, 06:34 PM   #8
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Quote:
Take a primed piece of brass, turn it upside down, and hit the primer with a hammer and punch.
Bad idea.

Quote:
Not to be a safety nazi but I would avoid the hammer and punch trick. Tried it as a kid and picked a lot of small bits and pieces of primer cup and anvil out of my bleeding finger.
Sounds like you were lucky nothing hit you in the eye.
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Old February 27, 2015, 06:34 PM   #9
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Take a primed piece of brass, turn it upside down, and hit the primer with a hammer and punch. It's as loud as a gun shot. So I assume most of the "bang" is the primer going off.
Nope, not even close. The primer alone is pretty darn quite compared to a loaded round.
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Old February 27, 2015, 06:40 PM   #10
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Quote:
Many years ago, someone told me the noise you hear after a lightning bolt goes off, is not the actual lightning but rather, the air rushing into the vacuum created by the lightning. I believe this is called, thunder.
The noise is the shockwave created by the super heated air expanding outward

It has nothing to do with any vacuums.

Gunshots are the same
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Old February 27, 2015, 06:42 PM   #11
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Very lucky, a lesson I have remembered my whole life.

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Old February 27, 2015, 08:14 PM   #12
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I had about thirty cases that were primed and ended up getting water in them. Rather than load them or deprime live primers, I popped them all. Open side down on a piece of cardboard. Only damage was the black round spots on the cardboard. Glad I had my ears and eyes on. Maybe not the best idea (as some have said), but nothing happened. And certainly none of the anvil came flying up (not sure how it even could).

If it ever happens again, I'll measure db level. Sounded exactly like live rounds.
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Old February 27, 2015, 08:38 PM   #13
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The noise is the shockwave created by the super heated air expanding outward
Exactly.
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Old February 27, 2015, 08:41 PM   #14
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When I was a kid, my cousin and I took 22 LR bullets and pulled the bullets with plyers. We then whacked the cartridge with a hammer on the concrete carport and received a sizable bang for our efforts. Seemed great sport until a brass fragment launched into my cousins calf. Left a nice circular little hole as a momento of our endeavours. That (like a firecracker) is sound made by a pressure wave. Lightening, on the other hand, isn't percussive in itself. The electrons flow several times from ground to cloud (or cloud to cloud) and back following an ionized trail. The trail collapses after the event is over and denser air rushes back into the former ion trail and this creates the "boom". Sorry, for the ramble. Hazard of being ex science teacher I guess.
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Old February 27, 2015, 09:44 PM   #15
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I know too much about lighting, sound, and the sound of primers.

I studied acoustics at the U of WA in 1976 with Kinsler's book 2nd edition. This is the 4th edition for free pdf
http://www.scribd.com/doc/165089542/...rey-pdf#scribd

The manager of the Boeing lightning lab, Omar, is 2008 said that the company I worked for could have free hour of lab time if they sent ME again.
Not only am I more fun than most engineers that design things to be lightning proof, but I told them the price per hour of all the other lightning labs.

In 1994 I saw a medical electronics researcher throw a stick over a high Voltage power line with a #36 wire [like a human hair] trailing to the ground. The column of ionized Copper looked and sounded like a lightning bolt. It blew a 5 foot deep post hole like hole in the ground, nearly broke the guy's ear drums, and sunburned one side of his face. I kept that secret 21 years. That's long enough.

In 2002 I was experimenting with how small a powder charge has to be to sound like a BB gun instead of a firearm. This is the threshold of supersonic gas escapement and is approximately one atmosphere above ambient at the muzzle at the time of bullet escapement. I found that with a Colt Commander 45acp with soft lead ball, no amount of powder was small enough. Just the primer made enough gas to fill the chamber and bore with 2A of pressure.

If you want gun noise theory. That section in that book about "spherical radiation from a simple source" is very much like the 2A peak wave that propagates from a ball of supersonic muzzle gas when it slows down to the speed of sound and propagates a wave. All guns have the same loudness at high frequencies. The ones with bigger gas balls have more low frequency content. 22s are like tweeters. Cannons are like woofers. The low frequency roll off is below 1/2 wave length = diameter of the gas ball at propagation.
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Old February 27, 2015, 11:21 PM   #16
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Cannons are like woofers.
Q: What caliber = "Brown Note"?

A: Dunno about caliber, but if you are obviously the target ....... THAT one.
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Old February 28, 2015, 09:26 AM   #17
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The military classification for these noises...

Precursor,
The nose the mechanical parts make,
Trigger unlatch, Hammer Noise, Firing pin noise,
Primer/Ignition noise,
Bullet traveling down the barrel (Harmonic Noise)
The air in the barrel escaping as the bullet pushes it out,

Muzzle Blast/Overpressure,
The sound of the bullet exiting a hollow tube,
The super heated gasses slamming into the outside air,
The sound the outside air makes when muzzle blast cools, and outside cold air rushes into the void cooling gasses create.

Post Exit Noise,
The cycling of the bolt in semi-auto weapons.
The harmonic vibration of the barrel settling down after firing.
Cycling of the bolt in manual bolt firearms...

Ballistic 'Crack',
The bullet exceeding the sound barrier,
And dropping back through the sound barrier as it slows.

(Disregarded: Is the sound of the rifling grooves on the bullet hitting the air column since there isn't anything you can do about it.
Anything with rifling is going to make that 'Whizzing' noise)

I don't know the specifics of all this, just read a study of noise and how the military tries to suppress some of this noise.
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Old February 28, 2015, 11:24 AM   #18
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I have shot .22 air rifle pellets out of a .22Hornet rifle using only the primer for propellant. The sound was mostly the click of the firing mechanism followed by the sound of the pellet hitting the target. It's actually quieter than most air rifles, although to be fair, most air rifles are more powerful.
I measured 350-450 fps depending on the brand of primer used.
I imagine if I shot these loads out of a pistol length barrel, the report would be louder and possibly the velocities would be higher.

I'm pretty sure the thunder of a lightning bolt is due to the expansion of air as it gets heated from room temperature to 10,000+ degrees in an instant. If the air simply disappeared and the atmosphere filled the vacuum, I doubt it would be nearly as loud. Unlike pressure, which has no upper limit, the most vacuum you can have is zero pressure absolute.
Thunder often sounds like a rifle bullet crack because it's a line source explosion and not a point source. Take a lighting bolt one mile long with one end of it one mile away the other end two miles away. You hear one end of the bolt about 5 seconds after the explosion and the other end about 10 seconds after the explosion. A mile long length of det-cord would sound similar.

The noise of a gasoline engine is not the fuel exploding but the sudden release of pressure when the exhaust valve opens. Many of you may have noticed that an unmuffled four stroke engine has a throttle opening where the exhaust is pretty quiet. There is the point where there is no overpressure in the cylinder as the exhaust valve opens. If you close the throttle even more, the engine gets loud again because now there is a partial vacuum in the cylinder as the valve opens.
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Old February 28, 2015, 01:04 PM   #19
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Boy, oh boy.

On a gun site with a lot of expertise, people think that gun noise is caused by air rushing INTO the barrel?

Jim
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Old February 28, 2015, 03:58 PM   #20
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Lightning makes two different sounds. One is the compression wave from expanding air and the other is the collapse of the displaced heated air after the flash. Nothing like gunfire. Don't believe it? Google it and you'll get your answer from a source that is accurate and not a lot of guessers giving answers. I can never get over the fact that anyone thinks they can get a correct answer by asking a question on the internet. You'll get a correct one all right.....mixed in with a dozen or more incorrect ones. The trick is sorting them all out. Well, at least it's entertaining sometimes.
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Old February 28, 2015, 04:18 PM   #21
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If you've ever been fired upon in combat, or worked the pitts at a range you'll hear the supersonic *crack* of the sonic boom from the bullet & muzzle report *boom* separated by a second or two as the *crack* is right overhead, but the *boom* has to travel from the muzzle at mach 1 but the bullet is probably doing 2~3 times that.
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Old February 28, 2015, 04:29 PM   #22
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"...super heated air expanding outward..." Whoever told you air expanding outward makes sound waves is confused. It is the air slamming back after the supersonic projectile has passed. Said CRACK keeps happening until the bullet goes subsonic. Like wogpotter says, ever been in the butts of a military range?
Isn't the primer either.
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Old February 28, 2015, 05:20 PM   #23
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Actually there are several parts to a sonic boom as well.

The whole thing with supersonic travel is the air can't get out of the way fast enough so its compressed into a high pressure wave. That wave travels from immediately in front of, to part way behind the tip of the projectile, depending on how much faster than the speed of sound it is traveling. The "wall" of compressed air is the "sound barrier" & it makes the first pulse.

At the rear there is a second disturbance where air can't flow into the partial vacuum created by the passage of the bullet. When it can a split second later there is a second sound pulse.

Frequently they are so close together the ear can't differentiate & you hear a single 2-tone *cr-RACK* sound.

This is an excellent public domain shadowgraph of a supersonic bullet showing the effect.
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Old February 28, 2015, 06:00 PM   #24
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The noise from a rifle shot comes from a lot of areas. Hitting primers with a punch and hammer is stupid. I know one guy that had a .223 primer dug out of his arm. I have de-capped many hi-power cases by pulling the bullet, dumping the powder, and firing them in a rifle. I can assure you that in a confined space, a fired primer (LR) is quite loud, but there is not enough pressure created to have air rushing back in and creating the noise. I am old enough to remember when "Sonic booms" from jets was not illegal. This was also quite loud. This is the same "vacuum noise" you hear from a bullet going past you. I worked with suppressors years back and what they pretty much do is slow down the expanding gases so the noise level is deleted. If you are using ammo that leaves the suppressor above the speed of sound, there will still be a cracking noise from the vacuum the bullet leaves. Air rushing back in a barrel making the gunshot noise is a little far fetched.
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Old February 28, 2015, 10:03 PM   #25
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It's amazing how the photos of shock waves from supersonic bullets resemble the V shaped waves made by speed boats. It's actually the same phenomenon just in a different wave medium.

When a motorboat reaches the speed of the wave it creates, the bow rises up and the stern sinks down in the water as the boat has to climb a hill in order to go any faster. If the engine is not powerful enough to climb that hill, the boat is effectively stuck at that speed, more power just creates a higher wall of water for the boat to climb. If the motor can climb that hill and get over it, it can accelerate and plane.
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