Regarding the gas rings. The other day I took one of our 11.5" SBR uppers and ripped off all but (1) gas ring. Using M193 ammuntion it cycled all the rounds 100%. I did the same test about 2 years ago with a SIONICS midlength and a Surefire 60 round magazine. Weapon functioned just fine.

I suggest you contact BCM as there may be more happening here.