Purpose concern:  About the third spherical I get a light-weight hammer strike.  I have experimented with both equally H2 and H3 buffer weights.  H2 I had been only having one shot, H3 I now get two shots off.  I've tried this on two uppers, one particular carbine and one pistol, but using the very same BCG.  I purchased an aimsurplus NiB BCG,