I had a partial case head separation using a 1.8oz buffer

[stonehog]

So the Hornady factory load’s brass that's sectioned, after being fired through the 12” upper with a standard carbine buffer, RET, and spring, still shows signs inside of the case down above the web of a failure node?

What’s the gas port diameter on the 12” barrel?

If your feed cone is within spec and is supporting the cartridge, you need to get a Bootleg Adjustable Gas carrier probably, or another type of carrier with adjustable gas.

I like the Bootleg the best because I just dial the gas adjustment through the ejection port without having to disassemble anything.

I run the 12” Grendels on the fully-choked gas setting since I shoot suppressed. I have enjoyed literally 4 years of reliability with it suppressed, maybe one quick cleaning of the BCG and chamber.

I’m using an extra power carbine-length recoil spring from Franklin Armory. You could also use a Geissele 42 coil woven spring.

I’m using a standard carbine buffer, 2.9oz/82grams.

The other 12” I built is using a Maxim PDW short RET with shorter, stiff action spring, Bootleg carrier, same barrel.

These barrels are 12” Faxon pipes spec’d by BluntForceTrauma for the group buy we did, with correct gas ports and feed cones.

I just checked a bunch of brass I have shot through it and do not see any unusual signs.

The other 12” has had 4 years of hand loads run through it using Lapua and Hornady brass shooting 107gr SMK mostly.

Both have been run suppressed the whole time with high efficiency TBAC Ultra suppressors, which tend to be harder on the cyclic rate if the action isn’t tamed.

The Maxim PDW RET, spring, and tiny buffer (also 2.9oz) actually runs smoother than the standard carbine RET with extra power spring and 2.9oz buffer, from my shooting perspective.

That little Maxim PDW set-up was one of the smoothest-shooting ARs I have felt, which was counter-intuitive due to 12” suppressed CLGS.

I don't quite want to give up on this barrel yet as it's light and a great shooter - easily the most accurate grendel I've had yet. Hoping I can tune this with the block and heavier buffer. The block is a bit coarse. Full cycle and lock back at 2 turns open - when I backed it off a quarter turn, no lock back. I may try 1/8th but it might be time for a superlative block or something nice. If/when I go that route, I'll measure the port.