Took my 300 blackout 10.5 inch to the range today and had a couple issues. Trip was to tune the gas block running subs. Process- 1 round per mag until the BCG locked to the rear. Setup - Carbine gas/ Seekins adjustable gas block/ Sig M400 BCG, Barrel is 10.5 purchased from Classic Firearms as "us manufactured" but when asked said Bear Creek Arsenal 1. After chambering a round, the bcg & charging handle became next to impossible to extract the round. I had to use the bench to knock it loose if I wanted to eject/extract the live round. This didn't happen on every round though...Im struggling to figure out what could have caused this. 2. After several different sub loads and gas block almost completely open the BCG would only lock back on an empty mag if I ran super sonics. I figured this was due to the buffer which is an H2. Though im not ruling out issues with the BCG Any suggestions on a different buffer to try and reasons why the BCG lock up would have happened?