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

[LRRPF52]

Some recent testing and pics. I have another pistol lower with a regular carbine tube and buffer (2.9oz). I took the Odin 12" out with the Odin bolt (I re-measured headspace and it passed fine - no idea what was going on earlier) and shot some Hornady Black factory loads (same bullet) and then a couple of my A2520 reloads. One of the 2 A2520 handloads had the ring, but a few of the Hornady cases also had a less pronounced ring starting, so I'm starting to think that I need an even heavier buffer (H3) on this CLGS setup.

I also pulled the remaining 9 that were left in the kaboom box, and segmented a Hornady case, and the 40th pre-kaboom case that had a ring. There is definitely a ridge inside the Lapua case.

The first pic is left to right: Lapua A2520 shot in carbine lower, Hornady black shot in carbine lower, and Lapua A2520 shot in pistol lower (1.8oz buffer)

The second and third pics show the Hornady black case from carbine lower and Lapua case from pistol lower. I didn't segment the Lapua case from the 2.9oz buffer (yet). Interesting that the outside rings are forming in different places (just above where the web ends, I bet). I have an adjustable buffer that I'll set up this week and do some more testing. Next up are heavier buffer, and then a different bolt (monster).

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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.