HKMR556 10.4" Conversion cycling issues
My son acquired a new MR556 for xmas 19' while on leave. Shortly after he left it went straight to Marvin Pitts of Nefarious Arms, to be chopped to 10.4" and re-profiled. Just picked it up on the 27th of June and we function tested it before he went back. The rifle fires and extracts at about 3 o'clock but does not pick up the next round. Admittedly it feels stiff when running the action. I did some testing, the factory buffer is 5.01 ounces, so somewhere between an H2 and H3. The factory HK buffer spring is shorter than a mil-spec spring but noticeably stiffer. Ammunition is Federal XM855 62 Grain Green tips and should be hot enough.
As a test I also ran a Larue Spring, that I found out from springco, is their spring, that is stiffer then a mil-spec spring but in my gross estimation weaker then the HK spring. I ran this spring with an H2 Buffer, HK Buffer and a stander mil-spec buffer, all with the same results as above.
Second test was with the standard LMT Mil-spec spring, an H2 buffer, HK buffer and a standard mil-spec buffer. The gun functioned the same as above, except for with the standard mil-spec buffer, in which it function flawlessly and ejected at 4 o'clock as it should.
From my readings thus far, a really real world HK416 is supposed to be over gassed for reliability. I'm not sure what the MR556 gas port spec is but I'd assume the true 416 is larger...? I've tried getting a hold of Marvin to see if he'd opened the gas port up or if he thought it needed it, but I've left two messages. I could order the mil-spec spring and buffer but I'm not a fan of the firearm needing such weak tolerances to run. I'd rather it be over-gassed and deal with the issue accordingly. Additionally, isn't the HK buffer proprietary?
Any insight would be greatly appreciated.