Options for undergassed rifle.

[Heavy Metal]

I have heard Nickel-Boron finished BCGs need less gas to cycle too.

[uffdaphil]

AR-15 Buffer Construction Picture photo pic Chart Carbine Rifle Buffer Weights

Adding these terms to the thread should help finding the helpful comparison photo again. I too forgot that as a photo the words would not (I think) show in a thread search.

[Clint]

Is that martentrapper's 2nd 6.8 rifle?

I think the gas port needs to be opened up to the same size as the other rifle.

Don't make a light Franken-buffer or cut springs. The stock rifle buffer is actually good.

Other research shows:
20" 6.8 with rifle length gas uses a 0.1067" diameter gas port.

Try working up to that size.

[AKDoug]

Yeah, Clint that's the one. I sold him a lower earlier this year and I hate to see him have so much trouble. Constructer says he uses .093 gas ports on rifles. I advised MT to check and make sure his is as least that large.

I agree on cutting springs, but I figured changing buffer weight might be a reasonable avenue.

[Clint]

.093" is the standard gas port size for 20" rifle gas 5.56 barrels.

6.8 (and 300BLK) have shorter, faster pressure curves and will require bigger sizes with the same barrel and gas system length.

This faster pressure curve is also the reason an 8.5" 6.8 or BLK barrel with pistol length gas works fine, while pistol gas 5.56 barrels can be more troublesome.

[Clint]

No prob. The spacer takes up the space of roughly two steel weights. It weighs almost nothing.

EDIT: a mil spec rifle buffer just has 5 steel weights and the rubber spacer disks + 1 of the above mentioned aluminum spacers.

I have a buddy who shoots heavy 80gr handloads and he had me remove the spacer and insert two additional steel weights from a carbine buffer (I think it ended up between an A5H3 and A5H4 in weight....just above 6oz). He prefers to use the std power rifle spring and he has been quite happy with the results.

7 weights in a rifle buffer. That's a cool trick.

For reference, the slightly shorter AR10 rifle buffer contains 6 steel weights.