AR Pistol issues

[rumlover]

10.6g of 1680 with a 225 BTHP = 1080 at 60 deg/29.9 mmg/450'/67% humidity. Same load in a 9" AAC upper was drastically different. Also tried some other powders, but same results.

I've got a H3 buffer inbound now. Hopefully that fixes the issue. When I chrony the rounds, I'm not getting a drastic spread of velocities and accuracy is holding between 1-2 MOA depending on the load. That tells me the bullet is leaving the bore before the bolt unlocks, but not before the gas pressure completely drops.