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.
Bang
- Thread starter Bucksnort1
- Start date
"...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.
Isn't the primer either.
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.
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.
Gunplummer
New member
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.
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.
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.
When I'm cleaning the barrel of a muzzle loader, sometimes I will pull the cleaning rod out really fast and the vacuum in the bore make a high pitched "pook" kind of noise. You'll never confuse it with muzzle blast.
Sometimes that "pook" noise is followed by cursing and swearing because it sucked the patch off the cleaning jag and back into the bore, meaning I have to hunt for a worm (looks like a miniature corkscrew) to attach to the cleaning rod to fish the patch out of the bore.
Sometimes that "pook" noise is followed by cursing and swearing because it sucked the patch off the cleaning jag and back into the bore, meaning I have to hunt for a worm (looks like a miniature corkscrew) to attach to the cleaning rod to fish the patch out of the bore.
That pop sound from air rushing into the barrel when a cleaning rod vacuum is broken is not very loud compared to supersonic gas escapement.
The frequency of the sound from the bore can be calculated.
http://en.wikipedia.org/wiki/Helmholtz_resonance
When I lower the muzzle pressure to below 1 atmosphere above ambient by reducing powder charge, instead of a loud bang, I then get three sounds; the firing pin, the muzzle and the target being hit. Even under these conditions, air rushing in may not be audible, as the cooling of powder gases in the bore has a fall time slower than the resonance [will do a poor job of exciting it].
The frequency of the sound from the bore can be calculated.
http://en.wikipedia.org/wiki/Helmholtz_resonance
When I lower the muzzle pressure to below 1 atmosphere above ambient by reducing powder charge, instead of a loud bang, I then get three sounds; the firing pin, the muzzle and the target being hit. Even under these conditions, air rushing in may not be audible, as the cooling of powder gases in the bore has a fall time slower than the resonance [will do a poor job of exciting it].
The sound of a pressure vessel containing up to 55.000 psi getting uncorked when the bullet leaves the muzzle makes noise.
Has nothing to do with the bullet passing thru the air and it collapsing back into it's trail.
When you are downrange and hear the sonic crack of the bullet passing overhead, consider the report of the barrel coming split seconds later isn't caused by it.
Operating a suppressed weapon should be even more informative - the action clanks as it cycles, same as loading it for the first shot. And the bullet passing makes its own noise, the suppressor just knocks down the huge volume of high pressure gas as it escapes.
That's why we have mufflers on cars - suppresses the report of the cylinder opening and the high pressure gas escaping. It doesn't suppress the sound of the tires on the road, or the power steering pump whining.
A suppressor on a firearm doesn't quiet down the boots of the guy carrying it or the action cycling. Just the report of a small volume of explosive.
Has nothing to do with the bullet passing thru the air and it collapsing back into it's trail.
When you are downrange and hear the sonic crack of the bullet passing overhead, consider the report of the barrel coming split seconds later isn't caused by it.
Operating a suppressed weapon should be even more informative - the action clanks as it cycles, same as loading it for the first shot. And the bullet passing makes its own noise, the suppressor just knocks down the huge volume of high pressure gas as it escapes.
That's why we have mufflers on cars - suppresses the report of the cylinder opening and the high pressure gas escaping. It doesn't suppress the sound of the tires on the road, or the power steering pump whining.
A suppressor on a firearm doesn't quiet down the boots of the guy carrying it or the action cycling. Just the report of a small volume of explosive.
Typically, the pressure is much, much lower than that when the bullet reaches the muzzle, unless you are shooting a .223 caliber derringer with a 1 1/2 inch barrel.
With a 20" barrel, it's down to around 10,000 psi or so in .223.
There's a reason why barrels are thickest around the chamber.
Gunplummer
New member
Nonsense my ass. That is why so many people get hit by trains. You don't hear them coming. What do YOU think makes the snapping noise of a bullet passing? I can delete that noise from a well designed suppressed weapon just by running ammo that is traveling below the speed of sound. People are confusing two different sources of noise here. You can eliminate the the initial explosion of the round going off by slowing down the expanding gasses. The snap of a bullet can only be eliminated the same way, by slowing it down, unless there have been some radical new discoveries in the last 30 years.
If you take the trouble to read my post your question is answered already.
Trains don't depend on principals of flight, nor do they travel supersonically. If you ever ride a mach 1+ flying train your example might be valid. Most who get struck by trains are distracted & don't hear, or feel the vibration of them coming.
What you hear is the high pressure pulse from the leading edge(s) of the fuselage & wings, depending on design it may be 1, 2, or 3 pulses very close together.
If there were a vacuum there would be no pressure differential over the upper & lower aerofoil surfaces, no lift & the plane would drop like a brick instantly.
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Trains do not travel faster than the sound they make.
People get hit by trains for many reasons: some intentionally, some because because they are not paying attention/are intoxicated ..... they may not hear it over their blaring streo because much of the noise of a train emanates from under the train/behind the locomotives and is shielded from a listener ahead of it, and because the trains are moving faster than the person in front of the trains think they are, and they think they can "beat the train" across the crossing ...... in no case does the train outrun the sound it makes.