Can't get my suppressed 300 AAC AR quiet

[Haymaker]

This is my fist posting here, but I have been a long-time follower. There is a ton a great information here! My question is about trying to get my 300 AAC AR quiet using a Liberty Mystic-X suppressor quiet.

I don't have a way to measure sound dB's but if I put the Mystic-X on my Ruger American chambered in 300 AAC shooting Sellier & Bellot 200 gr subs the gun is very quiet. It's almost as quiet as shooting .22LR subs with the same can. I measured the muzzle velocity a from the suppressed Ruger American and it's going about 1030 fps @ 36F outside. A website I found said the speed of sound would be 1091 at 36F so my rounds are going subsonic.

The problem is that I can't seem to get my AR quite. I have a 16" 300 AAC upper and a 8.5" 300 AAC upper. I put an adjustable gas block on both uppers and completely closed the gas block. Both uppers will not eject the spent round with the gas block closed. The 16" 300 AAC is going around 1140 fps at 36F, and it's loud with the Mystic-X, but the rounds are going supersonic. However, the 8.5" AAC upper is going around 960 fps @ 36F, and it's still very loud. Again, neither upper will eject the spent round since I have the gas blocks closed, but both are very loud.

I thought if the gas block was closed I would get sound performance close to the Ruger bolt gun, but I'm not. I am not hearing action noise from the AR. It's a "bang" sound.

Any tips on what I can try next to get my AR quite?

[#40Fan]

Different ammo or start reloading. Some powder is just louder than others.

[cdhknives]

Short barrels are generally going to be louder because there is more unburned powder being dumped into your can and it is probably at a higher pressure when the bullet 'uncorks' the bore. The surprising thing is how much faster your AR is over the bolt rifle. Reloading to tune your MV to good sub range is going to help...and if you don't reload try different subsonic ammo. Every rifle is an animal unto itself...

[Haymaker]

Thanks #40Fan & cdhknives for the responses. It sounds like reloading is the solution here. That will be my next step into solving this problem. Again, thanks for the input!