Purpose challenge:  Over the third round I get a light hammer strike.  I have tried both H2 and H3 buffer weights.  H2 I had been only having a person shot, H3 I now get two photographs off.  I have attempted this on two uppers, 1 carbine and 1 pistol, but utilizing the exact BCG.  I purchased an aimsurplus NiB BCG, I am likely to attempt that