A side question about the sound.

Discussion in 'NFA Firearms and Accessories' started by Demi-human, Sep 28, 2020.

  1. Demi-human

    Demi-human Member

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    Another thread had me wondering a question.

    How loud is the supersonic crack of the bullet?

    I can hear it as it goes down range and perceive the location of the crack moves with the bullet, outside.
    But how loud is the crack inside?
    Considering it travels fifteen feet, inside, how loud is that?
    Is it perceptible over the suppressed report?
    Is it too fast for our hearing to perceive?
    Inside, without PPE, one hundred thirty decibels is loud! Does it cover the crack?
     
  2. jmorris

    jmorris Member

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    This is a video that’s not shot very far away. The ammunition exits right around the speed of sound out of that rifle.

    2 of the rounds in this video definitely went super, can you tell which two?



    The back ground noise is a jet some number of thousands of feet above, flying past.
     
  3. ogree

    ogree Member

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    How loud is the supersonic crack of the bullet?

    About 130 db.

     
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  4. Englishmn
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    Englishmn Member

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    Suppressed supersonic 223 sounds like unsuppressed 22lr out of a rifle.
    If you are close enough to the impact point the shockwave won't have time to form but its like within about 5-10 feet.
    I didn't measure just walked up to the berm until the crack stopped but it was pretty close.
     
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  5. 748

    748 member

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    The youtube channel "smarter everyday" did some high speed camera shots of the super sonic shock wave on 300bo both supersonic and subsonic rounds at a very large garage.
    The sonic boom and it's reverberations off the walls and concrete floor were incredibly loud.
     
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  6. 748

    748 member

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    Probably collected enough data to publish a white paper on this subject.
     
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  7. Englishmn
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    Englishmn Member

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    I would like to see a video of that like 20ft down range.
     
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  8. MachIVshooter

    MachIVshooter Member

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    It depends on the bullet profile and velocity. It may seem counter-intuitive, but the sonic crack of slower, larger, more blunt bullets like 9mm & .40 cal tends to propagate closer to the shooter and be much more offensive to the ears than that of a higher velocity, more aerodynamic projectile such as 5.56 or .308.

    I'll shoot suppressed .300 WM outdoors without ears no problem running my 1.6x9" Accipiter .30 model, but 115 gr. 9mm hurts my ears no matter what can or host is used.

    This is a 16" Armalite with one of my older can models firing M193

     
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  9. Demi-human

    Demi-human Member

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    Absolutely cool!


    So, in a room, even with a perfectly silent report, there will still be enough time for the shockwave to form around the bullet and fill the room with sound.
    But it will still be much less than an unsuppressed rifle.
     
  10. Demi-human

    Demi-human Member

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    Very cool video! :)
     
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  11. Demi-human

    Demi-human Member

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    Another interesting thing to know! :)
     
  12. Nature Boy
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    Nature Boy Contributing Member

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    Loud enough to need ear protection when in the pits pulling targets during a High Power match
     
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  13. Demi-human

    Demi-human Member

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    This was what I just thought of!
    Having never seen it done, I wondered.

    Thanks for the knowledge!:thumbup:
     
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  14. sparkyv

    sparkyv Member

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    Exactly.
     
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  15. 748

    748 member

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    The higher the BC for a certain bore diameter the slower the bullet will transfer it's energy to the air.
     
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  16. Elkins45

    Elkins45 Member

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    The difference when you’re shooting subsonic without hearing protection and then a round unexpectedly goes supersonic is painfully noticeable to me, especially when shooting under a roof at the range.
     
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  17. 748

    748 member

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    The way most bullets are shaped (not counting black powder spherical projectiles) and the way supersonic flow works you get the worst crack right around Mach 1.
     
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  18. CapnMac

    CapnMac Member

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    The higher Mach waves will also "crack" as they degenerate down to "merely" Mach 1. Which is why fighter jets have a double boom as they go supersonic.
     
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  19. LocoGringo

    LocoGringo Member

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    Are they claiming that an unburned granule of powder FROM THAT FIRED ROUND exited the muzzle before the bullet? So, to understand what they are claiming, a granule of powder started in the case behind the bullet, passed the bullet in the millisecond before the bullet entered the lands and grooves effectively sealing the bore from the chamber and achieved supersonic velocity ahead of the bullet as it traveled down the bore? Is that what they are thinking happened?

    I'm thinking it may be a granule of unburned powder from the previous shot that was deposited in the bore and it was pushed out by the air ahead of the bullet as the bullet suddenly traveled down the bore.

    Whatever the answer, it's interesting to postulate. I guess the only way to test it would be to fire a round, clean the bore to make sure nothing was left behind and then fire again. If another granule exited the clean bore, that granule of powder escaped past the actual bullet and traveled down the bore ahead of the bullet...maybe?
     
  20. Ranb

    Ranb Member

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    When I was lobbying for passage of the WA silencer use bill, I shot video of various rifles using supersonic ammo to demonstrate how "not quiet" they were. I had the camera set up down range and shot past it. 22lr, 17hmr and 308win all created loud whip cracking sounds as they past the camcorder.

    While a camcorder video played back on computer speakers is a poor way to evaluate gun sounds, I got the point across to the legislators who viewed the video that suppressed firearms can still be rather noisy.
     
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  21. Double Naught Spy

    Double Naught Spy Sus Venator

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    And this is a key point for most of the video as recorders often attenuate sudden loud noises. You can still tell that they are louder, but you really can't tell how much louder that they are.
     
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  22. Ranb

    Ranb Member

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    The noise of the supersonic bullet is louder than the muzzle blast when heard from down range. Here is a brief clip from a video I made years ago when I was trying to convince a MN state Senator to push a silencer bill.

    Two rounds of 22lr (CCI Blazer) followed by two rounds of 17hmr then 2 rounds of 7.62x51.

     
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