AR-10 .308 gas system lengths ?

DutchV · Feb 12, 2019

I'm looking at 18" .308 AR-10 barrels. Some come with mid-length gas, others have rifle length.

Is there a reason to prefer one gas system length over the other, assuming both barrels are decent otherwise?

DutchV · Feb 12, 2019

And would occasional use of a suppressor make a difference?

DavidA · Feb 13, 2019

Usually the further the gas port the less amount of gas provided the ports are the same. However they make ports different diameters to address the fact that you will get more gas pressure at shorter length. However at the same time length of barrel past port also comes into play. Suppressors also affect this as well. So as with all my AR10’s. Get an adjustable gas block, Odin Works makes some nice ones.

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alucard0822 · Feb 13, 2019

7.62 / 308 ammo has a huge range of burn rates and pressure, more dwell time from mid-length gas can help get the big bolt moving with fast powders and anemic surplus. Running good modern commercial and new production mil-spec ammo though, you shouldn't have a problem with rifle gas, and can turn the gas down quite a bit with an adjustable block while retaining reliability, and reducing recoil and gas blowback, especially with a suppressor. Port size, ammo and bolt/barrel specs will probably matter more than gas length though.

SWO Daddy · Feb 13, 2019

I did a bunch of research on this and everyone seemed to be saying to go rifle length on an 18".

I used mid length (on sale) with an adjustable gas block and it shoots soft as can be with no malfunctions. All AR10s should use adjustable gas blocks in my opinion. Gas length won't really matter then.

KIBarrister · Feb 14, 2019

SWO Daddy said:
I did a bunch of research on this and everyone seemed to be saying to go rifle length on an 18".

I used mid length (on sale) with an adjustable gas block and it shoots soft as can be with no malfunctions. All AR10s should use adjustable gas blocks in my opinion. Gas length won't really matter then.

Agree 100% - adjustable gas block is a must on large pattern ARs (and a good idea on all others)

KYtoMD · Feb 17, 2019

DutchV said:
I'm looking at 18" .308 AR-10 barrels. Some come with mid-length gas, others have rifle length.

Is there a reason to prefer one gas system length over the other, assuming both barrels are decent otherwise?

Either one should be fine, as long as you get an adjustable gas block (and all AR10s should have one).

AR-10 .308 gas system lengths ?

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