Just to update y'all on the feeding issues, it's still got issues, my feed rail extensions haven't made much of a difference after all. Something that did make a big difference was seating the mag box in place. The trigger guard wasn't holding it in place perfectly, so it would shift down slightly. Fixed that and it fed beautifully for 20 rounds (all dummy rounds) but then gradually went back to its old ways. I've worked on it more and it's better, but still not perfect. It feels like the top of the receiver is digging into the rim as the round is fed forward.

Sam