H3 in Dawn Marie's build, with a Rainier Match 14.5" pinned barrel, carbine gas system. That thing has some gas port magic going on, cycles factory supers fine, and run my 150gr handloads great. ((Hornady 150gr HPBT, cut down and resized 5.56 NATO cases, CCI 400 primers, 16.1 grains H110))
Had to work my 16" carbine gas NEMO Arms barrel over, in the buffer department. I went MagPul MOE Rifle stock and rifle buffer system on it. Wouldn't cycle some ammo, and wouldn't reliably cycle my 150gr handloads. The Rifle buffer is what is was. I had to lighten that thing up to about H weight to get it to cycle everything and lock back on a single round/last round. I'm going to convert that one over to the Spike's rifle receiver extension spacer, and just run a standard carbine buffer in it, with the trusty Armalite carbine spring.