Technical Question on Super Sonic Ammo and "Breaking the Sound barrier"

Discussion in 'Silencers' started by BigEd63, Sep 3, 2019.

  1. BigEd63

    BigEd63 G&G Evangelist

    Anyone know how far from the muzzle a bullet, lets say standard velocity 115 gr 9mm Parabellm, gets before making a sonic crack? I'm thinking as soon as it leaves the muzzle to a couple of inches maybe?
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  2. Junction15

    Junction15 G&G Evangelist Forum Contributor

    Just guessing on this, but I think it happens a short distance away from the muzzle. The gases are also supersonic and, very turbulent, exiting with the bullet as can be seen in hi-speed photos. That would be causing its own "crack" but also filling in the bullets wake for some small distance.
    Either way, the noise caused by escaping gases would totally eclipse any sonic boom the bullet makes until the bullet gets far enough ahead of the sound waves to be discernible.

    Come to think of it, maybe that's why we hear ka-boom instead of just boom? Dunno. I got work to pay attention to.

  3. TXplt

    TXplt Gun Toting Boeing Driver Forum Contributor

    None (it's generating a shock wave as soon as it hits supersonic velocity in the barrel). One it accelerates to supersonic speed regardless of where it is it's making a shock wave. The barrel has air in it just like the surroundings. Now there might be some interaction with the sides and the shock wave off the point and the dynamics of the barrel structure, and the sides aren't exposed yet, but once it hits supersonic speed it's making a shock wave.

    FWIW, this depends on the shape and on an aircraft, some of the structure is actually supersonic at high subsonic speeds.

    The bullet's highest velocity is when it leaves the barrel (or perhaps VERY shortly afterward in that there might be some continued pressure from the barrel acting on the bullet immediately on exit but this subsides very quickly).
  4. jerry

    jerry Since 03-15- 2002 Forum Contributor

    Good post. Interesting.

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  5. TXplt

    TXplt Gun Toting Boeing Driver Forum Contributor

    It's reaching a bit way back, but I do seem to remember the odd sound of the A-10 (brapp/brapp) where there were distinctive sounds generated by the rapid firing Gatling gun and the other was the supersonic crack of the bullets. Our 20mm probably did the same thing but wasn't nearly as big (and I was in the jet when firing it so wouldn't have heard the noise from the ground anyway). Didn't work much 20mm strafe as a GFAC but we did work the 30mm and I remember its distinctive (GREEEEEAAAAAATTTTT) sound.
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  6. runfiverun

    runfiverun G&G Evangelist

    actually it's possible for a bullet to be slowing down while it is still in the barrel.
    and it can be slowed down even further in an oiled barrel.
    because you will have a dieseling effect on the front edges of the bullet that will pop and snort from the created cavitation pushing back on those edges.

    the supersonic crack is heard as the bullet passes through the sound barrier.
    the air will build up on the front edge and has to be broken through that is what causes the 'crack' sound.
    you can hear it at whatever distance you happen to be standing at, and quite often hear it from the bullet passing by and then the boom from the muzzle if your at say 300yds.
    if your closer 20 feet you hear crackboom it's just not broken down into two sounds unless you listen for it.
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  7. Nodpete

    Nodpete G&G Evangelist

    It may surprise you to know that even a pellet gun can break the sound barrier. I had some very light weight pellets and with my Winchester 1000 .177 caliber air rifle you could hear the crack of the pellet. You have to get around 1200 fps to get to that point.

    I was basically shooting about 25 yds and could hear the crack as soon as I shot.
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  8. animalspooker

    animalspooker G&G Evangelist

    Really Nod? Is it loud like maybe a .22lr?
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  9. Ten Man

    Ten Man G&G Evangelist

    No, it would not be as loud as the .22, even at the same speed, because the "sonic boom" is created by the collapsing of the cavitation created by the leading and trailing edges of the object's pressure waves. The longer the object, or the larger the object, the more of a cavitation it creates, and the louder the "boom," up to a point.
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  10. Jay

    Jay Old man, No tact... Staff Member

    This is why accuracy suffers from a ding/damage to the barrel's crown..... as soon as the bullet is no longer in contact with the barrel, high pressure gas will exit the bore at the point of damage first, thus skewing the flight characteristics of the bullet. I proved this to myself by firing from a vise a junk .22 rifle with a damaged crown, recording the accuracy, then re-machining the crown, noting an obvious improvement n accuracy.
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  11. Nodpete

    Nodpete G&G Evangelist

    No, as Ten Man said it's not as loud as a .22, it starts out as a shrill whistle and then a soft 'crack'.
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  12. Jim Bridger

    Jim Bridger G&G Evangelist Forum Contributor

    The noise from the firearm is created by oxygen. The super heated gas is produced by smokeless powder. When the hot gas meets the ambient oxygen at the muzzle it explodes. This causes muzzle erosion in high velocity rifles.
  13. runfiverun

    runfiverun G&G Evangelist

    the hot gas causes the throat erosion at the other end.
    I'd bet money carpet has ruined more muzzles than gas erosion in the last 50 years.
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  14. FortyXDM

    FortyXDM G&G Evangelist Staff Member

    Lets find carpet and beat the ever loving tar out of him.
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  15. ChaZam

    ChaZam G&G Evangelist Forum Contributor

    All I have to offer to this thread is that my 3 supersonic foster kitties sound like horses when running on carpet down the hallway.
    (please excuse the mini-hijack). :)
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  16. My understanding has always been that the supersonic "Crack" starts at the leading edge of the object going supersonic and that it is the build up of sound pressure waves in front of the object that then break free similar to waves crashing over the bow of a ship with the shock wave trailing conically from that point again similar to the wave off of a bow.

    Not sure in the case of Bullets but in Aviation that is why Supersonic Aircraft have swept wings.. The swept wings allow the sound pressure waves to slide down the wings to the tips where they break free (again in a Conical pattern) to where they don't impact the tail of the aircraft and damage it (so long as the tip of the wing is out far enough for the length of the fuselage so that the waves stay in free air).

    If I remember correctly towards the end of WW II Fighter Aircraft had evolved enough that in a dive they had aircraft starting to experience damage from almost breaking the sound barrier to where Pilots were reporting that in dives the buffeting would sound like someone with a Jackhammer on the tail of the aircraft, with the buffeting getting worse the closer you got to the speed of sound until the aircraft "Broke Through" the Sound barrier (hence the term "Breaking the Speed of Sound") which didn't happen but they got close.

    Chuck Yeager in the Bell X-1 was the first person to actually break the sound barrier if I recall, and the X-1 was still a straight winged craft. If you read his account of it that's exactly what happened .... Rough as Hell until they broke through then smooth as Glass (the X-1 was built like a Tank to handle it because at the time they didn't fully understand how to mitigate it).

    We hadn't yet figured this out at the end of the War, which is why our first Jet Fighters had pretty much unswept wings (like the P-80 Shooting Star), and it wasn't until we got the Treasure Trove of research information from Nazi Germany at the end of the War that we figured it out (though I think we would have, it's just that the German's pretty much already had). Also if I remember correctly our F-86 Sabre was almost a Straight wing design with the wing sweep added very late in the development after evaluation of German data from the ME-262 (the Sabre was not considered a Supersonic fighter, but it was not a stranger to going Supersonic on occasion).
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  17. TXplt

    TXplt Gun Toting Boeing Driver Forum Contributor

    The T-38 (very similar to the F-5) is a supersonic trainer and has an 'area rule' (aka Coke bottle) fuselage. This assists in mitigating drag from the shock wave. The F-111 was extremely fast because it's variable geometry (aka swing wing) design allowed the wings to be swept anywhere from 16 to 72 degrees -- hiding a great deal of the drag at very high speeds where the fuselage (which would actually ride the shock wave) generated substantial lift (our fastest 'high and fast' profiles were to get to 600 indicated with the wings all the way back in max grunt in the climb and ride the wave up).

    Jet engine intakes on fighters have a relatively elaborate scheme of spikes or ramps/diverters to keep the shock wave out of the compressor section (on the F-111 it was a spike that moved aft and down to divert the shock wave occupying a substantial portion of the already small intakes when going way fast; it was powered by utility hydraulics and you could blow it forward subsonic if hydraulics failed to keep the engine from compressor stalling).
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  18. jerry

    jerry Since 03-15- 2002 Forum Contributor

    Your making me drool.
    38 was my first training bird at Chanute AFB. 629d88ed2af99297-photo.jpg

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  19. The F-14 was similar with it's swing wings, can't remember the full range though, but I do remember that they had an additional sweep position farther aft for more compact storage on an aircraft carrier to where they were actually in the movement plane of the Horizontal stabilizers. The Tomcats had Ramps that dropped down from the upper intake with the F-4 Phantoms having plates anchored at the Fuselage side that moved outwards, But I'm not sure on the original F/A-18 Hornets though as I was definitely not a Hornet Fanboy!
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