Can guns that shoot supersonic bullets be silenced?

[Wichaka]

For centerfire rifle, this is about as quiet as it gets. 308 Hog Hunter, shooting 180gr Sierra roundnose at about 950 fps. When listening to the shot, compare the shot noise, to the sound of the brass hitting the table top.

There is an impact shot on a water jug at 50 yards. Not the massive destruction you would see with full throttle loads. When shooting paper, I use 1/2 inch shoot 'n see repair pasters as targets. Very accurate. As you can see, not exactly "cat sneeze" quiet. Not a gallery load to shoot in your back yard.

That's good for 308, I'd be happy with that.

 

[hq]

Most any round can be suppressed to a level that the only noises you hear is the striker click, whizzing sound of the bullet in flight and, finally, the bullet striking the target, the last of which being by far the loudest. Semi autos can be very, very quiet too, providing that the action opening is delayed enough for the chamber pressure to drop so that the expanding gases from the breech are at an inaudible level, leaving just the sound of action working.

The key is to have sufficient suppressor chamber volume and gas flow characteristics to contain the high-pressure gases and release them through the muzzle opening in a controller manner. This is highly round-dependent, some produce higher pressure and more gas volume than others. Handloads with drastically reduced amounts of fast powder are the way to go.

As far as supersonic rounds are concerned, the flight noise, supersonic crack, is inevitable, but reducing the muzzle report makes it much harder to determine the direction where the shot came from by listening alone. Soundwaves travel perpendicularly from the flight path and direction of the bullet so the shot may well sound like it's fired from a completely different direction than it actually is.

That's just about it in a nutshell. The majority of my guns are suppressed, one way or another, and more often shot suppressed than not, regardless of the velocity of the ammo.

 

[MachIVshooter]

Most any round can be suppressed to a level that the only noises you hear is the striker click, whizzing sound of the bullet in flight and, finally, the bullet striking the target, the last of which being by far the loudest.

Not hardly.

.22 LR subsonics can be made that quiet with integral cans; I built one with a ported 9" barrel and 10" worth of suppressor that qualifies. .22 LR subs with a good screw on can will get down into the 115 dB range, which is pretty quiet for an impulse noise. 9mm and .300 blk subsonic get close, around 125 dB. .45 ACP will run in the 130 dB range from a good can, hearing safe but very much audible. Supersonic rifle rounds will run in the high 130s to 140s plus the sonic crack; much more pleasant than unsuppressed, but still unmistakably a gunshot that can be heard from considerable distance.

Modern suppressors are very effective, but Hollywood is Hollywood, and they recycle the same fake baby sneeze suppressor sound along with giving every gun the SAA cocking sound.

 

[Arizona_Mike]

The muzzle blast and the sonic boom are similar in sound intensity from the perspective of a distant observer. For the shooter, the proximity of the sonic boom makes it much louder.

An observer is going to hear the sonic boom coming from the point of nearest approach of the bullet's trajectory which does not reveal the location of the shooter (and can mislead an inexperienced observer) but it will still be clear that it was a gunshot.

Mike

 

[toivo]

Can guns that shoot supersonic bullets be silenced?

Yes, but the bullets can't.

 

[labnoti]

With a gun that fires a bullet using gas pressure from the burning of smokeless propellant, there are indeed two sources of loud sound: the combustion and pressure wave erupting from the barrel, and the atmospheric wave off the supersonic bullet. Diffusing the pressure wave out of the barrel is effective at reducing the muzzle blast noise, but the question is can the sound wave erupting off the supersonic bullet also be suppressed? That's the $247.5 million question. NASA has awarded a contract worth that to Lockheed to develop a supersonic jet that's quiet: the X-59 QueSST. The objective of the program is to achieve this with the shape of the aircraft. The "sonic boom" heard on the ground associated with supersonic planes is a result of how shock waves and expansion waves interact with one another to create the compressions we hear. It is totally conceivable to tailor the shape of a bullet or artillery shell to change the sound signature so that it's heard differently. The shock and expansion waves would still be produced, but a shape could be developed that caused them to diffuse and those waves would be heard as compressions with a much lower pressure level. In the jet version, they're anticipating a reduction from 106db to as little as 65db. That's not engine noise, but the sound pressure level of the shock waves heard on the ground level.

 

[hq]

Modern suppressors are very effective, but Hollywood is Hollywood

I'm not talking about SFX rather than load development. My personal subsonic round selection includes, among many others, .308 Win and .375 H&H loads that are firmly in "cat sneeze" category with run of the mill 300-550cm² internal volume, chambered cans. And I'm by no means an expert in this field, just applying principles developed in 1960's and 70's by minimizing pressure and gas volume at the muzzle with tiny loads of fast powder in R1/N310/Titewad category and making sure the V0 stays well below 1000fps.
The difference in muzzle report between the usual "recommended" slow powders for the calibers and much faster burning ones is nothing short of staggering. You can even load SWOS rounds using the same principle, which seem to be an all but forgotten art form nowadays.

Ironically, Hollywood is kind of right about this, just not the equipment they portray it's being done with.

 

[hq]

Some links...
How to handload subsonic rifle cartridges (and survive) (Part I of article series)
The use of sound suppressors on high-powered rifles

 

[JeffG]

Some links...
How to handload subsonic rifle cartridges (and survive) (Part I of article series)
The use of sound suppressors on high-powered rifles

Very good references.

 

[jmorris]

With a gun that fires a bullet using gas pressure from the burning of smokeless propellant, there are indeed two sources of loud sound: the combustion and pressure wave erupting from the barrel, and the atmospheric wave off the supersonic bullet.

Even if you are “firing” a projectile subsonic from a “moderated” air rifle, it will still make noise as it goes down range.

 

[Catshooter]

hq,

What does "SWOS rounds" mean? It's probably obvious but I can't figure it out.


Cat

 

[hq]

SWOS = Silent without suppressor. Extremely low muzzle pressure subsonic loads, usually 800-ish fps or less.

 

[SamT1]

Shooting suppressed 308 win at coyotes they don’t know where it’s coming from past 300 yards. They know to run, but don’t know what direction. The confusion makes them slow trot instead of B line to the nearest cover. I’d say that’s a valuable hunting tool. It takes some load development to find a load that minimizes the sounds from the muzzle blast. With some testing you can get it hearing safe. Not silent but quiet enough not to disturb people .

 

[CDR_Glock]

I have one on a 300 blackout, and the sound is knocked down enough not to require hearing protection.

I tried my pistol Suppressor, and the supersonic ammo is decreased enough to not require hearing protection. Subsonic is much quieter, though.

When we shot my friend’s Ruger Precision 308, it was pretty darn loud. But the recoil was markedly reduced.

22 LR from a pistol is quite with standard ammo, but supersonic CCI Stinger is noticeably loud.

I have yet to try 5.56 mm subsonic to determine noise.

I acquired four suppressors total, but one is an integral Suppressor in a Ruger Mark IV Target.

 

[Ryanxia]

The supersonic round does indeed create its own break in the sound barrier, that being said, on the right setup a suppressed supersonic round can be surprisingly quieter than you would think. I've shot suppressed .223 supersonic rounds where I didn't mind it as much, probably was not hearing safe but depending on your application, its a lot more hearing safe than un-suppressed.