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Old January 30, 2007, 08:12 PM   #1
1911austin
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Sonic Cracks and distance

Does anyone know about how far a supersonic bullet travels before creating the “supersonic crack”? I was shooting a suppressed 5.56 last weekend. We shot in into a sand trap from only a few feet away and there was no crack. Shooting at about 100 yards there was a crack. I realize the bullet design and velocity will determine how long it will take to get a pressure wave setup and to break the sound barrier. I’m just looking for some sort of “rule of thumb” for what I should expect. Basically, at CQB distances within a house, what are the odds of getting the sonic boom?
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Old January 31, 2007, 05:18 PM   #2
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If you are shooting with a can you should be using subsonic ammo, WAY quieter! And a bolt will always be quieter than a semi or full, unless its a intergal.
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Old January 31, 2007, 05:39 PM   #3
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a majority of 5.56x45mm NATO fired from a suppressor equipped rifle is not with subsonic ammunition....all those SF guys you see in Afganistan with a M4/2000 hung on their M4 is using standard ammo.
While I cant tell you what the rule of thumb will be on producing a sonic crack inside a building with 5.56..I know that a 9mm will.
On a battlefield the sonic crack has a different sound out on the wrong end
...its a moving noise that makes the firer's direction hard to pinpoint....they may run straight at you firing back over their shoulder thinking they are running away from the danger during a night ambush (using night vision gear.) also if fired closely down a line of telephone poles the bullet will make the crack noise as it passes each one. its an odd phenomena.
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Old January 31, 2007, 08:00 PM   #4
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If I'm not mistaken you wouldn't ever hear the sonic crack from a bullet you shot because of the way in which the high pressure wave (due to the supersonic flight) propagates. In this picture you can see the pressure waves due to a moving jet and how the build up on each other as speed increases until supersonic speeds are reached and you get the high pressure reagion which extends outwards from the jet. Since you would hear the boom when that region swept over you, and it never sweeps over the area directly behind the jet (or bullet in this case) you the shooter (and those standing withing a few feet of you) shouldn't hear the sonic crack at all.
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Old January 31, 2007, 10:42 PM   #5
Dave Haven
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I've shot my MAC-10 9mm with a can numerous times. I can hear the sonic crack from the bullets.
As p99guy stated, "On a battlefield the sonic crack has a different sound out on the wrong end
...its a moving noise that makes the firer's direction hard to pinpoint...".
Muzzle blast makes the firer's direction easier to pinpoint.... BUT.. A muzzle brake re-directing the muzzle blast can make that more difficult. I've heard accounts of animals looking around trying to figure out where a shot came from and which direction to run when the shooter was using a muzzle brake.
For ultimate quiet, subsonic bullets are needed.
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Old February 2, 2007, 01:18 AM   #6
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Not a personal observation, but

I have read that at suppressed rifle fired along a line of telephone poles will make the crack as the bullet passes each pole. Supposedly you hearing the crack has to do with the proximity of the bullet to a solid object.

I have heard the crack of rounds fired in my direction. We were trained to count between the crack of the bullet going by and the boom of the muzzle report, as a method of determining how far away the rifle was when fired.
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Old February 4, 2007, 01:07 PM   #7
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I've shot a MP5SD (full auto) with standard veloicty ammo and it was damn quiet. Also the USP .45, Beretta M9, and HK UMP.45 all with standard ammo and they were loader than I expected (the last one full auto). Each can is different, as to the design the maker uses. I have fired a Bowers CAC on a Ruger 10/22 and on a 77/22, same can, two different animals using Sniper Sub Sonic ammo. On the 77/22 the loudest sound was the bullet hitting the tree. On the 10/22 there was a little hiss as some gases escaped from the action opening, but nothing the intended target would be able to hear.
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Old February 4, 2007, 06:29 PM   #8
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The factory integrally suppressed MP-5SD has holes drilled into the barrel to bleed off gas...all full power 9mm bullets comes out of its muzzle at subsonic velocity because of that. Operators have had failures to stop with the SD model because unlike the other MP-5 models it has basically the power of a
.380acp(all the time) also the decible reduction of the integral suppressor is no longer close to state of the art. That is why you dont see the SD all that much anymore...everyone uses a regular MP-5 with a QD muzzle can and 147gr hollow points instead.
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Old February 5, 2007, 02:32 PM   #9
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But it is a kick in the pants to shoot full auto!
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Old February 5, 2007, 03:00 PM   #10
Zak Smith
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Quote:
I have read that at suppressed rifle fired along a line of telephone poles will make the crack as the bullet passes each pole. Supposedly you hearing the crack has to do with the proximity of the bullet to a solid object.
You're probably hearing the echo off the posts.
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Old February 5, 2007, 04:46 PM   #11
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During 'Desert Phase' of ranger school, we were fired at/over by a SAW at distance.
As we were not expecting it, most of us crapped out pants and ducked. The RIs laughed, and a second or so later, the report arrived. Kinda sounded like shots in the distance.

The sonic crack was much louder than the actual muzzle report at that distance.
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Old February 6, 2007, 02:55 AM   #12
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Only experience with suppressed guns I have is with a 10/22 and a 1911. The 1911 didn't make a sonic crack obviously. The 10/22 on the other hand loaded with super sonic ammo was a different story. I really didn't notice any change in the sonic crack at different distances. Of course I don't shoot things up close because I am too scared of debris bouncing back and hitting me. What I noticed was just how loud it is when the bullet hits a hard object. We were shooting some old thick PVC pipes and I could hear the impact from 50 yards (or however far away I was) away.
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Old February 7, 2007, 12:02 AM   #13
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The noise of the sonic crack is kinda overrated IMHO. Yes it is there, but it is not that noisy compared to the muzzle blast and any target is going to have a much harder time trying to locating you.
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