How loud is the supersonic crack?


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Owen
September 3, 2008, 01:20 PM
If a supersonic bullet passes, say, 6 feet away, how many dBa is it?

is it velocity, projectile diameter, projectile length, or number of shockwaves dependent?

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ny32182
September 3, 2008, 01:26 PM
Exact dB levels I don't know; nor have I ever stood 6 feet away while a bullet passed me down range, but I can tell you this: Based on watching full velocity rifles .223/.30cal being fired with a good suppressor on, I will say that the supersonic crack is indeed distinctly audible when isolated, but doesn't even hold a candle to the sound of the muzzle blast. When shooting an unsuppressed rifle, you can't hear it. It is completely drowned out by the muzzle blast.

Jim K
September 3, 2008, 01:28 PM
It is a shock wave, the same thing as a "sonic boom" caused by a jet aircraft. It is not so much dependent on bullet shape as on velocity.

How loud? I don't know but I have "worked the pits" and it is certainly noticeable as a loud "crack", like a .22 rifle being fired a few feet away.

Jim

rcmodel
September 3, 2008, 01:34 PM
I have been that close both in basic training, where .30 cal MG's were fired over you while low-crawling through an obstacle course.
Also, military rifle ranges while working in the target pits.

A .30 cal bullet crack is plenty loud enough to know for sure it just went buy! Not really that loud though. Kind of more a "Snap' sound.

rcmodel

ctdonath
September 3, 2008, 01:35 PM
Can't tell you dB, but can tell you that an AR15 with silencer (i.e.: muzzle blast suppressed) sounds like an unsuppressed .22LR, as does roughly a .30-06 bullet passing nearby fired from 300m away.

jnyork
September 3, 2008, 01:39 PM
I shot highpower rifle for years, and from being in the pits I can tell you it is pretty loud, you want your ear protection for sure.

Owen
September 3, 2008, 01:51 PM
In a specific case, I know a an unsuppressed rifle ~163 dBA, and with a suppressor, it is ~142 dBa.

What I really want to know is, with a perfect supressor, that eliminated 100% of the muzzle blast, so there is only the crack, how loud would the gun be?

Artiz
September 3, 2008, 01:56 PM
Watch this video, we can hear clearly the crack: http://ca.youtube.com/watch?v=WNwecxMlvog

hso
September 3, 2008, 02:02 PM
Owen,

I think the closest you're going to get is the difference between a suppressed rifle and an unsuppressed rifle.

I don't even recall seeing a calculation for what you're asking for.

Owen
September 3, 2008, 02:04 PM
guess I'll have to figure out how to measure it.

Vibe
September 3, 2008, 02:11 PM
about 140db


http://guns.connect.fi/rs/bulnoise.GIF

http://guns.connect.fi/rs/measure.html

hso
September 3, 2008, 02:34 PM
I think it would be the difference between the peak total and the max subsonic component since that subsonic component would be what was left from the muzzle blast of the rifle used in the graph.

You'd need to have an octave band analysis done and subtract the subsonic from the supersonic, but you may get roughly the same results as subtracting the max subsonic from the total peak on the graph shown above (regardless of whether it was fired from a suppressed rifle) if you assume the subsonic is from the unsuppressed muzzle blast. i.e. 140 - 115 ~ 25 dB

Jim Watson
September 3, 2008, 02:37 PM
Looks like Vibe has it. If you want field test information, all I can say is to go to a real rifle range and put a sound meter on the edge of the target pits. Time of flight will separate the muzzle blast from the bullet shockwave.

It is also interesting to hear overhead fire from a subsonic bullet. A .45-70 at 550 yards just kind of "whizzes" by.

Travis McGee
September 3, 2008, 03:27 PM
Having worked the pits and otherwise heard supersonic riflle and MG bullets passing overhead a few feet, I'd say it was more of a "snap" or "crack" than the BOOM or BANG of the muzzle blast.

From a sniper's POV, the good thing about suppressing a rifle is that muzzle blast gives away position, but sonic crack does not. In fact, sonic crack alone often confuses the "recipients" about the location of the shooter, and sends them looking in the wrong places.

Langenator
September 3, 2008, 03:34 PM
When I've worked the pits, I was never sure if the cracks I heard were from the passage of the bullets through the air, or the sound of them striking the targets.

The one time I could distinctly ID the sound of bullets passing was on a Bradley platoon live fire gunnery range, where the 25mm sabot (training) rounds were passing a couple hundred yards away (the targets for the Brads were located a good distance from the bunkers the infantry squads were assaulting, for safety reasons), and the crack was quite distinctive, and came from a very different direction from the sound of the 25mm guns firing.

Deanimator
September 3, 2008, 03:40 PM
Standing in the target pits, I find the supersonic crack of a 6.5-.284, .308, or .30-06 fired from 600 yards to be fully the equivalent of a .22lr handgun fired next to me. I find it intolerable without hearing protection.

hso
September 3, 2008, 03:41 PM
put a sound meter on the edge of the target pits.

That won't give an accurate measurement because the standard instruments won't capture the ~.35 millisecond "crack" because they're too short. You'll need a laboratory grade instrument capable of measuring impulse noise with durations as short as a tenth of a millisecond.

Owen
September 3, 2008, 03:49 PM
thanks Vibe, that's exactly what I needed.

brickeyee
September 3, 2008, 09:08 PM
That won't give an accurate measurement because the standard instruments won't capture the ~.35 millisecond "crack" because they're too short. You'll need a laboratory grade instrument capable of measuring impulse noise with durations as short as a tenth of a millisecond.

Even the measurement of muzzle blast amplitude is off with normal dB meters.
The bandwidth of the circuits in these devices is simply not adequate to capture the actual peak noise intensity.

The noise exposure time- intensity tradeoffs also fail for gunfire.

James T Thomas
September 3, 2008, 09:21 PM
For you AK-47 fans; the "crack" is not what I would call loud, that is intensity, but it is distinctly attention getting! And from the AK, unique, I might add. I have heard up to 12.7mm from the wrong end, and I knew immediately the enemy's gun. It has a shock wave with it, and you can sense the damage it will inflict.

I suppose you know, but the boom, boom, boom comes a moment later, unless you are unfortunate to be close up to one, and the time delay between the crack and the gun report can be used to estimate what the range is to the shooter.

Some of the replies are referring to muzzle blast. The near passing of a bullet intended for you is a deadly "crick, crick, crick," as it sounded to me.
Not much acoustical energy; decibels, but it get's your attention.

I know there is a lot to admire about the AK, but I hate them.
It may be irrational, but I can't dismiss it.

No one ever needs to shout "hit the dirt."

Loomis
September 3, 2008, 09:30 PM
Sonic booms are different depending on the size and speed of the object.

When you crack a whip, you are actually creating a mini sonic boom as the tip of the whip breaks the sound barrier.

17HMR have very small "sonic booms".

Aircraft sonic booms can make your house shake and break your windows if they fly low enough and fast enough.

MachIVshooter
September 3, 2008, 09:35 PM
Watch this video, we can hear clearly the crack

All I hear is the muzzle blast that escapes the supressor behind a supersonic bullet, and the echo from the woods.

Artiz
September 3, 2008, 09:42 PM
Aircraft sonic booms can make your house shake and break your windows if they fly low enough and fast enough.
I can assure that, a couple of months ago there was the Quebec Air Show, this was the greatest air show ever, Blue Angels, Thunder Birds, Red Arrows, Snow Birds, and the Canadian Demo CF-18 who was supposed to fly just under the sound barrier, unfortunately, this nice pilot broke it just a little and released the gas at time, because we saw the "white cone" sourrounding the aircraft, mannn... add to the sound of a flying F-18 a broken sound barrier, you get hands on ears, omg that was loud, really loud.
So a bullet creating a shockwave is NOTHING.

misANTHrope
September 3, 2008, 09:49 PM
^

FYI, the "white cone" appearing around the aircraft is not indicative that the speed of sound has been broken. That cone of condensation appears at about .95 Mach or so. I wasn't there, so I can't say for sure, but I doubt you actually heard a sonic boom. The sudden onrush of sound after those high-speed passes they do at shows is pretty intense, but nothing like an actual sonic boom. And if a pilot at a show inadvertantly broke the speed of sound, he'd almost certainly end up in some deep doo-doo.

Carry on. :)

Artiz
September 3, 2008, 10:03 PM
He wasn't low, he was really high, I mean, really (ok sky's the limit), so we lost a bit of sound, but I think it was supposed to happend (in these shows they like to tell you something and doing the opposite) because he climbed to the point that we could'nt see him, and then we saw (I saw, other people were looking dead center, lol) him coming from the left, really high too and I'm pretty sure he (maybe not) broke it a little to freak us (can we say broke the sound barrier a little? lol), because we clearly heard a really nig noise after we saw the cone (I said "hands on your ears!" to my friend, he said what? I said Do IT!) and then BANG! We heared it, we feeled it.

230RN
September 4, 2008, 01:44 AM
Standing in the target pits, I find the supersonic crack of a 6.5-.284, .308, or .30-06 fired from 600 yards to be fully the equivalent of a .22lr handgun fired next to me. I find it intolerable without hearing protection.

I concur. I likened it to a 45 going off about fifteen feet away,though. The very first time I worked the pits, I wondered why everyone had hearing protection.

First shots, I knew why.

Thing I remember most, visually, was the little flakes of paper, black on one side, white on the other, floating down in the morning sun, kinda blinking on-off as they fluttered down in the light.



Vibe, thank you for digging up that excellent information.

General Geoff
September 4, 2008, 06:11 AM
A good example (http://www.youtube.com/watch?v=annkM6z1-FE&feature=related) of just how loud sonic booms can be, even from afar.

Owen
September 4, 2008, 07:45 AM
I'm not using a normal sound meter. :-)

Deanimator
September 4, 2008, 10:19 AM
Thing I remember most, visually, was the little flakes of paper, black on one side, white on the other, floating down in the morning sun, kinda blinking on-off as they fluttered down in the light.
I recall taking my turn in the pits during the 1,000 yard events at Camp Perry on the points where people didn't know how much to come up on their sights to get to 1,000 yards. Instead of a "crack, thump", you'd hear "thud, thump" when instead of breaking the sound barrier overhead, followed by the sound of the shot, the bullet would hit the sandbag or the berm, followed by the sound of the shot. In those isntances you'd often have sand in your hair and close where the bullet cut the sandbags.

A friend was there for an Ohio Rifle and Pistol Association 1,000 yard "fun shoot" that a bunch of .45-70 shooters attended. He said that instead of "crack, thump", you'd hear "whizz, slap, clunk, boom" as the 300-500gr. bullet would go overhead at subsonic speed, followed instantly by the bullet hitting the target at an acute angle, followed by the bullet penetrating the tin roof of the target shed (which at the time was immediately in front of the pits), followed by the sound of the shot.

230RN
September 4, 2008, 07:18 PM
I recall taking my turn in the pits during the 1,000 yard events at Camp Perry on the points where people didn't know how much to come up on their sights to get to 1,000 yards.

IIRC, I had to go up about 34 clicks on the sight of a Garand. Looked like an antenna, sticking up there. As someone else reported recently as to how he did it, a buddy of mine and I also went up to the Grasslands and tediously measured out 1000 yards with a 100 foot tape, and he hid behind a hillock near the target with binocs and reported strikes by walkie-talkie.

Dialed it right in.

PTK
September 4, 2008, 07:21 PM
Check out my video of an AR-15 with and without a silencer. Most of the sound with the silencer is the supersonic crack. It's not hugely loud, but quite annoying nonetheless.

http://www.youtube.com/watch?v=vvQUhzMHk98

brickeyee
September 4, 2008, 08:24 PM
Jets at air shows routinely have on jet at some point go supersonic and create a sonic boom.

It is pretty rare to fly near Mach 0.95 without going above the speed of sound since aircraft operating at Mach 1.0 is very difficult and dangerous.

From about Mach 0.95 to around 1.05 buffeting is severe and the controls are less than smooth (as Chuck Yeager found out many years ago).

As the air flow over portions of the plane exceeds the speed of sound the shock waves form and then attach.
The Bernoulli equation stops to work since it does not allow for the standing pressure waves generated by faster than sound media speeds.

Aircraft usually accelerate through Mach 1.0 as quickly as possible. Shallow dives can even be used to minimize the time spent in the transonic region.

Big Boomer
September 4, 2008, 11:35 PM
didnt read the other posts but an easy way to think of it is that a bull whip that "cracks" is actually a miniature sonic boom. So Something quite small can be pretty loud. Sounds like a small firecracker.

The tip of the whip can easily exceed the speed of sound.

popoyskie
September 4, 2008, 11:42 PM
ok guys thanks for the post that info is what I need.thanks!!!

AnthonyC.
September 4, 2008, 11:48 PM
I have a pellet gun the can make pellets go supersonic, they are not loud, i actually enjoy the sound, it sounds like a .22 but Im sure that a bigger caliber rifle will be much louder.

BammaYankee
September 4, 2008, 11:53 PM
What's interesting is the variety of sounds bullets make. As Jim K can attest, when working the pits at a high power match, you begin to be able to tell if the round is coming in super versus sub sonic, stable versus tumbling, and even relative distance all by the sound they make. You also learn to hug the wall real quick when you here the 'pzzzzyt' sound when a round clips the steel target frame! I saw one hit the ground no more than 5 feet away not too long ago! Oh yeah.... Good idea to keep that info from your wife! Otherwise you'll find your 'honey do' list surprisingly long the morning of the next match!

Raccoon
September 5, 2008, 03:52 AM
I found this video to be an excellent example of supersonic crack.

http://ca.youtube.com/watch?v=otKhQMolH48

Skip forward to 3:50 for the specific supersonic crack demonstration, where two different rounds are compared in a suppressed muzzle.

230RN
September 6, 2008, 01:05 AM
AnthonyC mentioned:
I have a pellet gun that can make pellets go supersonic, they are not loud. i actually enjoy the sound, it sounds like a .22 but Im sure that a bigger caliber rifle will be much louder.

If this is a regular old pellet gun, not designed to shoot those new light pellets over the speed of sound, it may be an indication that you are using too much oil in the piston or the wrong kind.

Too much oil can result in "dieseling" in the piston chamber (where the oil spray or vapor ignites) and cause the pressure to go too high, damaging the seals.

I've got an old Feinwerkbau where this dieseling happens if I get too generous with the oil. Smells like a diesel truck when it goes off. Don't know if the lead pellets are going supersonic, but the sound is much louder than normal.

Stevie-Ray
September 8, 2008, 12:30 AM
I can assure that, a couple of months ago there was the Quebec Air Show, this was the greatest air show ever, Blue Angels, Thunder Birds, Red Arrows, Snow Birds, and the Canadian Demo CF-18 who was supposed to fly just under the sound barrier, unfortunately, this nice pilot broke it just a little and released the gas at time, because we saw the "white cone" sourrounding the aircraft, mannn... add to the sound of a flying F-18 a broken sound barrier, you get hands on ears, omg that was loud, really loud.
So a bullet creating a shockwave is NOTHING.Size matters, of course, in bullets as well as planes. The sonic boom from an FA-18 pales in comparison to that of an F-4 or even an F-14. We witnessed several sonic booms over the Detroit River just a few weeks ago during the Gold Cup quals. 2 FA-18s from an eastern demo team put on a rather cool show. But nothing like the old days of air shows. And an SR-71 lays down a horrendous sonic boom even at 80,000 feet. In size, compared to a fighter jet, it is gigantic. If you could completely quiet the muzzle blast of a .460 Weatherby, I'm sure it would be far louder than a suppressed 5.56 Nato.

AnthonyC.
October 25, 2008, 11:42 PM
AnthonyC mentioned:

Quote:
I have a pellet gun that can make pellets go supersonic, they are not loud. i actually enjoy the sound, it sounds like a .22 but Im sure that a bigger caliber rifle will be much louder.

If this is a regular old pellet gun, not designed to shoot those new light pellets over the speed of sound, it may be an indication that you are using too much oil in the piston or the wrong kind.

Too much oil can result in "dieseling" in the piston chamber (where the oil spray or vapor ignites) and cause the pressure to go too high, damaging the seals.

I've got an old Feinwerkbau where this dieseling happens if I get too generous with the oil. Smells like a diesel truck when it goes off. Don't know if the lead pellets are going supersonic, but the sound is much louder than normal.

Its not an old gun, its a new Gamo Big Cat, The pellets came with the gun, and I dont think I am going to be feeding my pellet gun a steady diet of supersonic pellets.

jakemccoy
October 26, 2008, 05:01 AM
Great tech thread, all threads should be like this, straight tech.

moooose102
October 26, 2008, 07:53 AM
i would think that its volume would be in direct relationship to its size. a bullets sonic boom would be much less than a jet airplane, which would be much less than the spce shuttle, which would be much less than a 2 mile diameter asteroid. in many cases, SIZE DOES MATTER!

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