quietest suppressed centerfire pistol carteridge

[rifleman 1981]

I have been playing with a few sub sonic pistol callibers lately, and it seems the larger the caliber the more noise you get, sub sonic or not. Has anyone else noticed this??? I put my aac suppressor on a 9mm and it almost sounds like a co2 air pistol, my 10mm subsonic is louder, and my 45acp is louder yet!!! anyone else ever play around or experimint with different powders and bullet combos and have any luck???

 

[Glocktogo]

I have been playing with a few sub sonic pistol callibers lately, and it seems the larger the caliber the more noise you get, sub sonic or not. Has anyone else noticed this??? I put my aac suppressor on a 9mm and it almost sounds like a co2 air pistol, my 10mm subsonic is louder, and my 45acp is louder yet!!! anyone else ever play around or experimint with different powders and bullet combos and have any luck???

The difference you're noticing is a direct result of the bore diameter of the gun and suppressor. A 9mm bore is only 88% of a .40 bore and only 78% of a .45 bore. Those are significant percentage increases that allow more of the expanding propellant gasses (which are supersonic even though the bullet is not) to exit the suppressor. This is one of the reasons a suppressed turnbolt .308 sounds so mellow. The exit bore on that is only 68% of a .45.

So long as the efficiency and volume of a suppressor can effectively handle most of the propellant gasses, what you're left with is what is directly behind the bullet upon exit, and the bullet itself if supersonic. A bullet with a high Ballistic Coefficient (BC) will be quieter than one with a low BC, because they generally displace less air. What air they do displace is less turbulent. So a short fat 230gr .45 bullet is naturally going to be louder than a long skinny 147gr 9mm bullet.

Just remember, the bullet and powder aren't actually making noise. The noise comes from how they move the atmosphere they're moving through, and how that atmosphere closes the void left in their wake.

The only way to make a suppressed .45 quieter is to use faster burning powders that expand as completely as possible withing the barrel and suppressor, or use less powder overall. Keep in mind that faster burning powders will also burn more completely before the action unlocks than a slower powder. Some of the noise you're hearing is coming out the back end and not the end of the can. If you watch a pistol firing in low light on a high speed camera, you'll usually see propellant gasses burning as they come out of the ejection port, particularly if it's a hot load. One caveat would be to use enough powder to get the case mouth to expand, sealing up the back end better. The more propellant gasses that leak out around the case, the more soot you'll have in the gun and a corresponding increase in noise (though slight).

 

[rifleman 1981]

so, everything is relative to bore size and not bullet weight??? reason I asked is cause my 9mm seems quieter than the 300 whispers I have shot but I am not an expert by any means, whisper was on an ar platform, 9mm was a sig 229 srp pistol

 

[338Shooter]

There are a lot of factors. Baffle efficiency has an effect on how big the bore can be. The more efficient the design, the quieter the can even with a bigger bore. Look at what AAC did with the Ti-Rant. Simple K baffle design, but they made it work better and the .45 can is beating most if not all the 9mm cans DRY. The baffles cause the gas to take the volume of the can instead of just jetting right though. The better they do this the quieter it is going to be and the effect of the larger aperture is going to be reduced.

Volume, Baffle Efficiency, Bore Diameter are all things that contribute to the effectiveness of a suppressor. You can have a huge suppressor with a poor baffle design that won't work for squat no matter what the aperture is.

 

[Farmall]

Not to hijack the thread, but the science behind suppressors is fascinating. I've read more about how they work more than I've used them.