I’m using an aero precision upper with a BCM bcg. I initially had issues with FTE , turned out the BCM bolt only came with an ejector spring. I used an o-ring with the spring and haven’t had any issues after that. Have about 1k rounds through it so far and has cycled great. Using a standard gas block, with a H2 buffer I believe. I think it’s 4.6 oz . Also using a sprinco buffer spring (blue?) . Pretty consistent 3-4oclock ejection pattern. Barrel is ballistic advantage 1:7 twist. 7.5” with a Midwest industries blast can and a 9” Aero handguardNice - any specifics on the upper you would like to share? Also what weight buffer did you use.