I've got a AR 5.7 upper and a SWR Spectre can for it. The gun has functioned flawlessly (800+ rds) w/out 1 jam. I have major feeding problems w/ the can on? I have also tried my M4-1000 on it w/ no luck. I know that it's blowback and not a DI gas system, and I used the supplied buffer w/ the...