Functionality concern:  On the 3rd spherical I get a lightweight hammer strike.  I've tried using both H2 and H3 buffer weights.  H2 I was only getting one shot, H3 I now get two photographs off.  I've tried out this on two uppers, just one carbine and one particular pistol, but utilizing the exact BCG.  I ordered an aimsurplus NiB BCG, I'm go