Originally Posted by Big Bird
I had a similar problem with my LMT SBR upper when I first got it and it gave me fits. When I finally broke down and called LMT the first question out of the tech's mouth was what weight buffer am I running? Well, and H2 of course...everyone knows you should run an H2 in a Carbine length gas system right? Nope. LMT drills their gas ports to cycle with a standard weight carbine buffer. So I replaced the H2 with a carbine weight buffer and the stupid thing has run like a champ ever since. Never skipped a beat.
I've seen various reports on what runs best in the LMT SBR uppers. I run an H2 in mine since I shoot mostly 5.56.
In this case, though, the bad key meant the buffer didn't make a difference. I tried it with a C buffer, and no joy.