Buffer weight and the 300 AAC Blackout

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meanmrmustard

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So, I have a quick question gents: What weight buffer should I use for a 16" Blackout upper with a pistol-length gas tube. Barrel is an ER Shaw, unsuppressed. Most of my shooting will be done with supersonics in the 110 to 125 weight range. My goal is to decelerate wear on my innards.

Any help is appreciated.
 
You'll want a standard carbine buffer, and I would recommend an adjustable gas block if you're looking to slow wear on internals and reduce recoil.

I have a 16'' Pistol Gassed 300blk. Very versatile configuration, but can be over-gassed while suppressed with supers sonic ammo. I installed an adjustable gas block and noticed a significant reduction in both recoil and overall violence with the brass.

If you adjust the gas block to gently cycle hot super sonic ammo, it will not cycle subs on that same gas setting - fyi.
 
Awesome. Thank you for the info.

Currently, its unsuppressed, and I may not add one in the future, and I'm using a standard carbine buffer.
 
Ive fired around 15,000 rounds of subsonic and supersonic 300 BLK through SBR's and 16" rifles. Ive never adjusted a gas block. Not once.
 
Wow 15k. Adjustable blocks must be pointless if you've successfully fired that many rounds without one.

I'll agree that they're not necessary if the intention is to make a gun fail proof in any configuration, with any ammo -but with a 16'' pistol gassed gun- the difference in recoil between -wide open- and -just enough to cycle the bolt reliably- is significant and most certainly addresses the OP's desire to "decelerate wear on his innards" :D
 
No need for the adjustable gas block with .300blk. Even with a suppressor. Carbine H buffer is fine.

The .300blk isn't hard on the BCG. Don't worry about that.

Every .300blk 7.5"-10.5" Ar I've shot was a pistol gas system.
 
Depending on the size of the gas port - and it's location in relation to the overall barrel length - the 300blk can be extremely over gassed! Specifically pistol gassed 16'' barrels... which is what our OP is building. Stubby barrels of 7.5-10'' with pistol length gas ports and how well they function aren't part of the concern here.

It is true that an adjustable gas block isn't ''necessary'' to make a gun simply cycle... but when the BCG is bottoming out in the back of the buffer tube with 5x more force than what's needed to cycle the gun, and the trigger is slapping your finger hard enough to bruise, restricting gas is a far better fix than switching out every different combination of buffer & spring.

All I'm saying is they exist for a reason... and if you get the chance to fire hot supersonic ammo through a suppressed 16'' barreled 300blk w/ a pistol port of .120 -wide open- you might find yourself looking into one of these 'silly adjustable gas blocks'.
 
Adjustable gas blocks serve a purpose. But not on an borderline undergassed 300blk with a stock wight bolt and buffer.

I have to have one but I'm running an aluminum BCG and pretty much no buffer at all
 
R.W.Dale said:
Adjustable gas blocks serve a purpose. But not on an borderline undergassed 300blk with a stock wight bolt and buffer.

I have to have one but I'm running an aluminum BCG and pretty much no buffer at all
Click to expand...
How is my system undergassed with a pistol gas tube on a 16" barrel?

Am I missing something?

Range was snowed out, and I refuse to pay for indoor ranges. So, it'll be a few days till I actually get to shoot it.
 
meanmrmustard said:
How is my system undergassed with a pistol gas tube on a 16" barrel?



Am I missing something?



Range was snowed out, and I refuse to pay for indoor ranges. So, it'll be a few days till I actually get to shoot it.
Click to expand...


Compare the port pressures for 5.56 vs 300blk. I don't think it's possible to overgas a 300blk

A pistol gas supersonic 300blk is only at about 2/3 rds of the port pressure of a CARBINE 5.56
 
horsemen61 said:
Why a 16 inch upper with a pistol length gas system?
Click to expand...
That's what ER Shaw had, and I've been sitting on the barrel awhile before building the upper around it.

As I read, its seemingly a popular choice, but I'm not getting specifically what weight buffer folks are using.

I'll assume its a viable option, otherwise I wouldn't see other makers offering pistol length on 16" barrels in 300 blk. I suppose at this point its trial and error as to the best buffer weight.
 
I'd sell the barrel or cut it down. An adjustable gas block does not make up for the port being in the wrong spot. Should be a carbine gas system for 16".

Most of us have been drilling the ports, not choking them off with an adj gas block. .300blk just doesn't seem to have as much gas to offer. (larger barrel diameter effect?)
 
Last edited:
Zerodefect said:
I'd sell the barrel or cut it down. An adjustable gas block does not make up for the port being in the wrong spot. Should be a carbine gas system for 16".
Click to expand...


NO!!!!!

A carbine 300 blk will only run supers with any semblance of reliability. A pistol gas is the standard and will run both. A rifle length gas system will not run at all

A 300blk only has a fraction of the port pressure of 5.56 Gas system "rules of thumb" for this round go out the window.

OP compared to any length 5.56 you are undergassed an adjustable gas block is not going to do anything for you, they're primarily for overgassed guns like mine
 
R.W.Dale said:
NO!!!!!

A carbine 300 blk will only run supers with any semblance of reliability. A pistol gas is the standard and will run both. A rifle length gas system will not run at all

A 300blk only has a fraction of the port pressure of 5.56 Gas system "rules of thumb" for this round go out the window.

OP compared to any length 5.56 you are undergassed an adjustable gas block is not going to do anything for you, they're primarily for overgassed guns like mine
Click to expand...
Wow. I honestly did not know that.

I'll not be cutting my barrel. I figure ER Shaw knows there stuff, and AAC offers a comparable barrel. I assume it'll be reliable.

Thanks for the info Dale. I'm keeping tabs on your build.
 
R.W.Dale said:
NO!!!!!

A carbine 300 blk will only run supers with any semblance of reliability. A pistol gas is the standard and will run both. A rifle length gas system will not run at all
Click to expand...


My SIG M400 with the carbine gas system has had several thousand subsonics and several thousand suspersonics though it without a hitch.

In any case an adjustable gas system is has a place on a .223 . Not on a 300 BLK. It wont help. It wont hurt either.
 
I dont have an adjustable block, that's why I'm asking about buffer weight to counteract possible overzealous bolt thrust.

Edit to add:
I went to 300blktalk.com with this question, and they said dont sweat it and to bump up buffer weight according to recoil impulse, and that the 16"/pistol gas is AOK. Only way to test is to shoot, and the range is closed. Wah.
 
Last edited:
Zerodefect said:
I'd sell the barrel or cut it down. An adjustable gas block does not make up for the port being in the wrong spot. Should be a carbine gas system for 16".

Most of us have been drilling the ports, not choking them off with an adj gas block. .300blk just doesn't seem to have as much gas to offer. (larger barrel diameter effect?)
Click to expand...
The folks at Arf Com disagree.

Most of them seem to prefer the versatility of the pistol length gas system as opposed to the carbine length.

Not cutting the barrel.
 
I have built two 300 BO rifles with carbine gas and non adjustable block which to date have collectively fired 2000+ rounds of supersonic ( bullet weights from 110 to 168 gr.) ammo without one failure of the gas system. A third AR is a pistol with a 12.5" barrel and pistol gas, it too has not had any failures contributable to over/under gas. All three run a standard carbine buffer, gas port holes have not been measured and two barrels are CMMG and one Rainier. I have no intention of running any of my AR's in subsonic category so the standard buffer will work just fine.
Another SBR assembled for my buddy uses pistol gas on a 8.5" barrel with a suppressor and once a proper load was developed it too runs flawlessly with a carbine buffer.
 
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