Quiet bullets

Discussion in 'Rifle Country' started by taliv, Mar 8, 2019.

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  1. taliv

    taliv Moderator Staff Member

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    https://www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html

    Although the attached link isn’t about shooting per se, it’s curious that they’re researching ways to eliminate the waves that compress to form the supersonic boom. If successful, I wonder if the same could be done for Bullets, resulting in mitigation or even elimination of the crack. I’m sure the shape of such a bullet would have lots of downsides wrt terminal ballistics and probably accuracy. But it would certainly be worth it to some of us who use suppressors a lot and value our hearing.
     
  2. RecoilRob

    RecoilRob Member

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    I don't think we shooters have much to gain in this area....being that triple supersonic projectiles in dense atmosphere are going to produce a strong shockwave with little available to us to mitigate it. NASA is trying to 'spread out' the bow wave with the long and skinny pointed nose so instead of a sharp 'BOOM' they're hoping for more of a muffled 'thump' as it passes by someone on the ground. The longer and skinnier you can make the point, the farther back the shockwave will form as the point penetrates the air without as much resistance.

    Picture a projectile with a needle the size of a sewing needle projecting from the main body....would it initiate a shockwave at the same velocity as one that begins on the body? Likely this would pierce the air more cleanly and the shockwave would begin back on the fatter portion of the projectile...but you'd still have a shockwave. Even subsonic projectiles can create shockwaves due to the flow being uneven over cannelures and such which will make a 'crack' though of less intensity than a conventional supersonic projectile. We need to stay well below the Mach to keep things quiet....and I'm pretty sure there's little we can do about it besides reducing the caliber and shooting very long and skinny needle like projectiles which 'should' be quieter at the same velocity as a normal fat bullet....but sooner or later it's going to compress enough air to create the shockwave and make some noise.
     
  3. Dr T

    Dr T Member

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    However, it does bring an interesting experiment to mind. Recall the old saw about how you never hear the report of the rifle (or crack of the bullet) that kills you.

    Given the relatively recent development of the very low drag profile bullets, I wonder what the sound pressure of one of those bullet cracks would be compared to a bullet of more conventional profile all other things being equal (caliber, weight, velocity)?
     
  4. Varminterror

    Varminterror Member

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    What jumps to mind for me: I have a burning suspicion (having thought a lot about this over the years) that these design features which would abate the intensity of the sonic boom would also yield a bullet which more happily passed through the transonic boundary. I expect if we analyze bullets known for transonic and post-transition stability, we’d see they have characteristics which also reduced the intensity of their sonic boom signature.
     
  5. taliv

    taliv Moderator Staff Member

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    the trans-sonic stability was my first thought too, but i didn't mention it because i don't really know enough to other than speculate
     
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  6. jmorris

    jmorris Member

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    Even subsonic bullets are not that quiet.

     
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  7. RecoilRob

    RecoilRob Member

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    If we could perform an experiment with two vastly different bullets, say a 58 caliber Minnie ball against a 77 grain .224, ...each gradually brought up to supersonic speeds I believe that the blunt and much less aerodynamic projectile would be much louder going by at the same speed. Many reports from the Civil War said that bullets 'whizzed' overhead...and this I've heard myself with black powder rifles. Sooner or later in the experiment one is going to start making the sonic 'CRACK' as it goes by...and my money is on the 58 to do it first. How much faster it will take to get the .224 to the same level of 'CRACK' I don't know...but would wager it's going to be going faster being that it punches a much cleaner hole in the air and lacks the multiple ribs down the sides each of which will create an additional shock wave at transonic velocity.
     
  8. taliv

    taliv Moderator Staff Member

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    even just measuring secant vs tangent ogives with very sensitive equipment would be interesting
     
  9. Newtosavage

    Newtosavage Member

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    Technology eventually looks more like nature as it evolves. Looks like a shark or sturgeon's nose.
     
  10. Riomouse911

    Riomouse911 Member

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    I’m confused...Are you discussing the sound a bullet makes in flight making a sonic boom that’s audible, or the report we hear from the muzzle when a projectile is fired? :uhoh:
     
  11. Dr T

    Dr T Member

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    The "sonic boom" ...
     
  12. jmorris

    jmorris Member

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    I drifted it with my post, sorry.
     
  13. Riomouse911

    Riomouse911 Member

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    No worries, I am still not sure what the technology the guys above were talking about will affect; the sound of bullet in flight or the report upon firing. I've seen the still and video images of the bullets flying through the air, just was wondering if making a bullet quieter would do anything for trajectory.
     
  14. Varminterror

    Varminterror Member

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    Largely we're passing time observing something cool NASA's working on for aerodynamic aircraft which has implications for all supersonic items in flight, like, perhaps, bullets.

    The article is reviewing a new nose cone design which is expected to reduce the sonic boom of aircraft. The transonic zone is a challenge for all things in flight, crossing into supersonic flight, and then falling out. So while the article seems to focus on a rather silly aspect of this issue - the sound signature - the implications of a smoother interface between the supersonic bullet or aircraft and the air around it are a lot more important than just reducing sonic booms. Reducing the destabilizing effect which happens to aircraft as they over and back across the transonic boundary would be a big win - I've seen videos of craft coming out of the air as they're in the transition, and we've all heard so much lore about bullets basically falling out of the sky as they fall transonic and subsonic and the flow fields shift the center of pressure relative to the center of mass.

    I'm not necessarily sure what we can do with that "razor edge" flat nose design relative to a rotating bullet, however, and it does appear they're working towards really long ogive nose designs and higher drag tails. But what may come out of this which could prove to be highly valuable in sporting ballistics, rather than specific transferable design features, are the computer modeling systems or aerodynamic measurement systems used in the testing and development process. 30 years ago, nobody was talking about doppler radar use in designing and measuring performance of bullets, today, even a sportsman hobbiest has access to this tool...
     
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  15. jmorris

    jmorris Member

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    I had a friend bring a telescope out to our range about 20 years ago and it was a real eye opener watching them make their way to the target with such magnification.
     
  16. Demi-human

    Demi-human Member

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    I wonder what twist it would take to fire such a javelin? Gain twist would make a comeback!

    The lead debate would be a non-starter, under those rotational forces only the mono metals could survive.
    Oh, but think of the excellent sectional density! A twenty two would end to end a bison! With subsonics...

    I know some have set bullets backward to make a caveman hollowpoint and "it works", but is there a limit at which the tail is "too pointy" to work correctly? Or pehaps at much too low an efficiency?

    (Thank God for THR. School is canceled again! :confused:
    But I'm secretly happy I got "free days off" with my kiddos. Twenty one of them... Seriously...)
     
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  17. taliv

    taliv Moderator Staff Member

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    i've always wanted to try bullets that were hollow cylinders. like a hole saw bit with the back end cut off. i wonder now what sort of shock wave that would produce
     
  18. jmorris

    jmorris Member

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    You just need to find some PMC ultramag ammo.

    They quit making it a long time ago though. I think it got banned back in the 80’s.

    B96CA8F2-7788-4FDC-8412-C550D59EFF7C.jpeg

    5EA22FAB-2B28-42E6-A38C-7AB9491C9D43.jpeg

    Supersonic for sure, the 38’s were 66 grain bullets.
     
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  19. taliv

    taliv Moderator Staff Member

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    why was it banned?
     
  20. taliv

    taliv Moderator Staff Member

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    and thanks for the pics btw!
     
  21. jmorris

    jmorris Member

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    It was deemed AP handgun ammunition.

    Looks like they did make a version that was OK though, I didn’t remember that.

    https://forum.cartridgecollectors.org/t/u-s-atf-ap-ammunition/15836

    I guess they looked at the entire projectile as a “jacket” so, 100% of it’s weight, was over the allowable 25%.

    That was at the end of 1986.

    https://atf-eregs.18f.gov/478-99/E9-527#478-99-c-8
     
    Last edited: Mar 11, 2019
  22. jmorris

    jmorris Member

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    They were not the first to come up with the idea though. The “Krnka-Hebler Tubular Bullet” for cal. .30 Ball cartridge (Krag) tested by Frankford Arsenal in early 1894

    E8B7291F-5857-4230-B44F-7010F33AE603.jpeg

    Or the last to play with them.

    3381352C-00C9-4CEE-99E1-3656C9B90840.jpeg

    CAA72246-83C0-43D1-9E4D-8D8640E7AE22.jpeg

    2B6889C9-39C2-4F35-904F-935AB68F63ED.jpeg

    2A4732A8-3620-4F15-B54E-20715A62568C.jpeg
    C05BBA98-AF3B-47A4-BA1B-EC112D5FB120.jpeg

    Key words for a search would be “ring airfoil bullet”, “cyclon bullet” and “tubular” bullet not to be confused with “totally tubular” from the 80’s as well, maybe that was the ‘70’s I think by the ‘80’s cool things were “radical”... ;)

    If you wanted to play with the idea yourself you might come up with some appropriate size fishing net weights you could drop in a sabot.?

    55CDEECE-1731-4F73-A907-7F065AD867F2.jpeg
     
    Last edited: Mar 11, 2019
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  23. RecoilRob

    RecoilRob Member

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    The problem with hollow bullets is that supersonic air will not go through them well and the Krnka-Hebler Tubular Bullet was found to be terribly inaccurate as well as offering a disadvantage with respect to range. Shockwaves are some weird things and supersonic air behaves about the opposite of subsonic...which is why aircraft need variable geometry intake ducts to run much above M1.6 or so. About the best we can do is a long needle point, smooth sided boat tail I'm afraid.

    What might offer some improvement would be a barrel that doesn't cut rifling into the jacket but like a polygonal type where the bullet should leave the barrel with smoother sides which might create less additional shockwaves.

    And...while I'm here, let me make a prediction: You'll not see supersonic aircraft regularly used for travel even if the NASA testing is successful in making the sharp 'BOOM' into a softer 'Thump'. Reason is fuel economy and even aircraft that can 'supercruise' don't do it very often just because it really eats the gas....not as bad as when using the burner, but still WAY more fuel than high subsonic cruise and this economy problem will doom any commercial use of the 'low boom' aircraft IMHO.
     
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  24. jmorris

    jmorris Member

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    Sabot rounds leave a bullet smooth but I haven’t found any that were very impressive accuracy wise.
     
  25. RecoilRob

    RecoilRob Member

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    Agreed. But...I think this is a case of bad implementation making a good idea seem to be a bad one. The SLAP rounds weren't known for stellar accuracy as well as the old 'Accelerators' proved to be dismal in just about any rifle they were tried. Some of this is an incompatible twist rate for the projectile and I wonder if the sabot wasn't actually twisting around the bullet as it went down the barrel and failing to initiate all the spin it had? If the sabot barrel had a proper twist rate and somehow the sabot could hold the projo tight enough to spin it up properly (and then release cleanly....a whole 'nother problem) there's no reason they couldn't have been accurate. But making a barrel specifically for the sabot round kind of defeats the whole purpose of the sabot round.:(
     
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