Have a 300 Blackout AR with 8" barrel suppressed with Silencerco Omega. Direct gas. My 220 grain subs are avging 925 fps with A1680. I know it won't be Hollywood quiet, but I'm getting loud pop like slapping dirty sneakers on a sidewalk. Does not hurt my ears. Is there anyway to make it a little quieter? I have a heavy JP silent captured spring on the way.

The Omega is a great suppressor, you can get it quieter but my advice if you want it under 120db an integral suppressor is the way to go. The quietest 300blk we have ever built was a ported 8" barrel that ended up at 14.5" with the suppressor, it metered 118db with Remington 220gr ammo. With the ported barrel the Remington 220gr averaged 890fps.
Joe

I feel like mine was quieter with AA5744 than with A1680, its also a significantly cleaner.

Propellant choice is the next step in finding quiet. You're looking for the propellant that yields the lowest bore exit pressure ... it will be the quietest. One approach is to find the fastest powder that will yield the desired velocity thus giving the least pressure at the muzzle.

The challenge is to find that fastest powder that will also not be prone to detonation (SEE) when small volumes of it burned in a relatively large case volume.

The fastest powder I've tried is 2400. Is faster than AA5744. (I have 2400 for handguns and AA5744 for cast projectiles in very large cases.) 2400 burns much cleaner than AA5744 and seems pretty quiet.

Changing the buffer spring arrangement will make a significant reduction in the noise you hear next to your right ear. Am not sure that noise can be heard very far away though.

eastern_hunter wrote:Propellant choice is the next step in finding quiet. You're looking for the propellant that yields the lowest bore exit pressure ... it will be the quietest. One approach is to find the fastest powder that will yield the desired velocity thus giving the least pressure at the muzzle.

The challenge is to find that fastest powder that will also not be prone to detonation (SEE) when small volumes of it burned in a relatively large case volume.

The fastest powder I've tried is 2400. Is faster than AA5744. (I have 2400 for handguns and AA5744 for cast projectiles in very large cases.) 2400 burns much cleaner than AA5744 and seems pretty quiet.

Changing the buffer spring arrangement will make a significant reduction in the noise you hear next to your right ear. Am not sure that noise can be heard very far away though.

This.

Suggested loads can be found here: http://quarterbore.com/300whisper/subsonic.html

Notice the ability to use 168/165 gn projectiles in a subsonic load. 2400 cycles my 10.5" suppressed.

Is it appropriate to treat sub-sonic 300 BLK as a pistol cartridge? Mind you, I'm not arguing for or against this, it just always struck me as, in essence, a pistol cartridge given the size and weight of the projectile, as well as the desired lower velocity, and all in conjunction with the shorter barrel. Well... short for a rifle.

Coltm4 wrote:

eastern_hunter wrote:Propellant choice is the next step in finding quiet. You're looking for the propellant that yields the lowest bore exit pressure ... it will be the quietest. One approach is to find the fastest powder that will yield the desired velocity thus giving the least pressure at the muzzle.

The challenge is to find that fastest powder that will also not be prone to detonation (SEE) when small volumes of it burned in a relatively large case volume.

The fastest powder I've tried is 2400. Is faster than AA5744. (I have 2400 for handguns and AA5744 for cast projectiles in very large cases.) 2400 burns much cleaner than AA5744 and seems pretty quiet.

Changing the buffer spring arrangement will make a significant reduction in the noise you hear next to your right ear. Am not sure that noise can be heard very far away though.

This.

Suggested loads can be found here: http://quarterbore.com/300whisper/subsonic.html

Notice the ability to use 168/165 gn projectiles in a subsonic load. 2400 cycles my 10.5" suppressed.

+1 on powder choices (also +1 on Curtis Tactical Cans!) I have hand loaded a wide range of powder/projectile combinations and found the correct balance of burn rates/gas/cycling ability plays a a big role in perceived sound & cycling AR. I have tested 4198, 4227, Reloader 7, 1680 & AA#9 and found AA#9 to be the cleanest & quietest powder (magnum pistol powder). The other powders don't fully burn, are dirty or very gasey. There is a ton of people on the handloading section of http://www.300blktalk.com/forum/viewforum.php?f=141 with a lot of great research/load combinations. I run a 10.5", Suppressed (Curtis Tactical Rebaffled Kestrel .308), SLR Adjustable Gas Block, JP Silent Capture. One of my quietest 190gr-220gr loads is 7.1gr-7.3gr AA#9 anywhere from 950-1050 depending on projectile.

TROOPER wrote:Is it appropriate to treat sub-sonic 300 BLK as a pistol cartridge? Mind you, I'm not arguing for or against this, it just always struck me as, in essence, a pistol cartridge given the size and weight of the projectile, as well as the desired lower velocity, and all in conjunction with the shorter barrel. Well... short for a rifle.

I always consider subsonic 300blk rounds as a 45acp with more streamlined bullet. Bullet weight and velocity very similar, ballistic coefficient much better.

Changing the weight of the projectile may allow more complete combustion and eliminate the pop.A faster powder should do the same.Can you regulate or turn off the gas to "hear" if that makes a difference.That could tell you if the spring upgrade or a heavy buffer will help.

I have found AA#9 to be noticeably quieter than any of the other magnum pistol powders I have tried, and I also catch a lot less blowback in my face. As a lefty this really matters to me, since I'm staring right into the ejection port with half my face every time I pull the trigger.

TROOPER wrote:Is it appropriate to treat sub-sonic 300 BLK as a pistol cartridge? Mind you, I'm not arguing for or against this, it just always struck me as, in essence, a pistol cartridge given the size and weight of the projectile, as well as the desired lower velocity, and all in conjunction with the shorter barrel. Well... short for a rifle.

Yes. Same speed/weight combo as my .40SW. 165/180/200gr @ 950-1085fps.

Just less initial frontal area.

Interesting ... AA#9 is slightly faster than 2400. Would probably have tried it too if I had any. Used the last of it some time ago Good powder for medium loads in 41 and 44 Rem Mags. Generally cleaner burning than 2400.

#9 is my preferred powder for heavy bullets in the 10mm so I try not to run low. It is becoming one of my favorite powders.

I'm going to try Power Pistol and Longshot in some heavy 300 blackout subsonic loads as well to see if there is a noticeable difference.

Powder choice can have a HUGE impact on noise levels at a given velocity. You want the fastest burning powder that will cycle the gun at the desired FPS. And for most that is several steps faster than A1680.

I have also metered powders against each other. I cannot measure actual dB but I can compare loads to loads. The quietest for my was IMR 4227. It was also least sensitive than Lil'Gun, H4198 and a off brand version of A1680. It is with MY silencer.

I started testing some other powders and Blue Dot works great in my gun. In a barrel longer than 10.5" the rounds will go supersonic in winter. But in summer they are amazing loads. I believe they are even quieter than my IMR 4227 loads.

Power Pistol is too fast to cycle an AR, I have tried. BTW, I had a friend try black powder and it ran fine.

The fastest powder I have used with 220's is N110, N105 could possibly work, but I don't like to get too close to maximum without measuring pressure. Sadly the round is too short for it to work with pressure trace in most guns. But the difference in charge weight is insignificant, so I haven't bothered with it.

TROOPER wrote:Is it appropriate to treat sub-sonic 300 BLK as a pistol cartridge?

Sure, why not? It's a sliding scale, not some fixed division.