Can't get my suppressed 300 AAC AR quiet

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Haymaker
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Can't get my suppressed 300 AAC AR quiet

Post by Haymaker » Sun Dec 02, 2018 11:45 am

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?

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dellet
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Re: Can't get my suppressed 300 AAC AR quiet

Post by dellet » Sun Dec 02, 2018 12:14 pm

Haymaker wrote: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?
For the 16” AR you need less powder.

For the 8.5” AR you need more barrel.

You need to make sure that your adjustable block shuts off the gas completely, some do not. This also may be part of the noise.

If you do not hand load, you will need to find ammo that will stay sub-sonic in the 16” barrel, again trial and error.

In general, factory ammo, in a factory AR, will be disappointing if you are looking for quiet.
300 Blackout, not just for sub-sonics.

cdl
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Re: Can't get my suppressed 300 AAC AR quiet

Post by cdl » Sun Dec 02, 2018 8:12 pm

Some of this obvious stuff isn't always immediately apparent so I apologize ahead of time if it's too obvious.

It's not the speed of the bullet that matters. It's the speed of the air getting out of the bullets way. Many figure around 1000 fps for the bullet to keep that air subsonic.

On average, half the bullets are faster than the average velocity.

An 8" barrel might have twice the muzzle pressure of a 16" barrel.

Less powder is quieter than more powder and some powders are quieter than others.

You probably need to take up handloading to do better.

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John A.
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Re: Can't get my suppressed 300 AAC AR quiet

Post by John A. » Mon Dec 03, 2018 12:20 pm

All of the answers above are correct, even if they're probably not the answers that you wanted to hear.

You can ask several here, I struggled getting my blk AR as quiet as I thought it should be when I started participating on the forum more regularly.

But out of the box, and with commercial ammo, from a lack of better description, it sucked. Sounded more like banging garbage can lids together.

I have no beef with the mystic, but it's also not one of the better blk suppressors out there either. The port is larger than better performing suppressors. matter of fact, the Liberty Leonidas is probably the best commercial can made for the blk that I have heard. I like Dave and he's done well and is doing basically what I did 10 years ago making a can that you can use on so many things, but the tradeoff to using the can on more items, is a less efficient can than one dedicated in that caliber. I say that with respect because I get why so many people buy it is because it's compatible with so many calibers. But blk is a 308-.310'ish caliber bullet. And the mystic is probably bored out to around .400'ish if I were guessing. That allows a lot more blow-through than a can with a tighter bore.

In the end, I had to tune my gun to the load that was worked up, I had to experiment with powders I had never used or imagined that I would use, and I had to build a dedicated can. I could show you a video of the difference in sound from the same gun using a long 9mm can I had made and been using for years, versus a long 308 can that I purpose made for it. The difference is very obvious.

Now that all is done with that gun, it sounds more like I think it should, and works well.

But I realize that's more than the average owner is willing or able to do.
When those totally ignorant of firearms make laws, you end up with totally ignorant firearm laws.

Haymaker
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Re: Can't get my suppressed 300 AAC AR quiet

Post by Haymaker » Mon Dec 03, 2018 5:25 pm

Thanks everyone for the response. I really appreciate the help and detailed responses. It sounds like reloading is the way to go. This will be fun and interesting to see if I can work up a load that will solve my needs.

cdl, you can never assume something is "immediately apparent", so thanks for the response.

John A., yes, you are correct. I purchased the Mystic-X because of all the compatible calibers. With that said I have been considering filling out a Form 1 and building a can just for the 300 blackout. That sounds like an interesting project as well, but will take a while to get my Form 1 approval.

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John A.
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Re: Can't get my suppressed 300 AAC AR quiet

Post by John A. » Mon Dec 03, 2018 5:36 pm

Paper form 1's are still taking 6 months or so.

Efile Form 1's are taking about 2 weeks.
When those totally ignorant of firearms make laws, you end up with totally ignorant firearm laws.

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dellet
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Re: Can't get my suppressed 300 AAC AR quiet

Post by dellet » Mon Dec 03, 2018 5:55 pm

This might be of interest.

viewtopic.php?t=98869
300 Blackout, not just for sub-sonics.

Haymaker
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Re: Can't get my suppressed 300 AAC AR quiet

Post by Haymaker » Mon Dec 03, 2018 7:40 pm

John A., thank you again for your response. I filled out a profile on Silencer Shop for their Form 1 service last week but have not submitted my application yet. Are you saying this only takes 2-weeks? That would be amazing. It took me 7 months to get my Form 4 back!

dellet, great thread and thanks for posting it.

Again, thank you everyone for your input. It's truly appreciated!

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John A.
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Re: Can't get my suppressed 300 AAC AR quiet

Post by John A. » Mon Dec 03, 2018 7:49 pm

It's taking about 2 weeks (typically less) for efile form 1's.

If you are using silencershop, you'll be at the mercy of silencershop as to when they submit your stuff.

They have a bad habit of holding onto paperwork and sending it when they feel like it.

When the changes to trusts took place about 2 years ago, they caused a huge bottleneck by waiting to the last minute to submit some papers to make a political statement. I'm not particularly a fan of theirs to be honest.

https://www.thefirearmblog.com/blog/201 ... lications/

I was serious about efiling only taking a few weeks right now. You're welcome to do an internet search.
When those totally ignorant of firearms make laws, you end up with totally ignorant firearm laws.

Haymaker
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Re: Can't get my suppressed 300 AAC AR quiet

Post by Haymaker » Mon Dec 03, 2018 9:02 pm

John A., thanks for the tip on Silencer Shop Form 1's. I found the eForm link on the ATF website and plan to go that route now. When I did my Form 4 I had the police print a few extra fingerprint cards. I'm hoping I can send ATF one copy to keep on file if I decide to build another Form 1 suppressor. Again, thanks for the help!

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