I expected to see more than that on the patch from powder not completely burned and case not completely expanded when the bullet left the barrel. As mentioned you normally see soot on the case if you don't get full case expansion. Might try shooting once then extract the second round. Feel for debris on the second round, look up the chamber/try the patch again.
You might try cleaning the upper/lower assemblies and magazine completely with something like Gun Scrubber. Possibly something carried in by the other rounds after being shaken loose by recoil.
If that doesn't work I don't know what to tell you. These guys might have some ideas:
http://www.ar15.com/
You might try cleaning the upper/lower assemblies and magazine completely with something like Gun Scrubber. Possibly something carried in by the other rounds after being shaken loose by recoil.
If that doesn't work I don't know what to tell you. These guys might have some ideas:
http://www.ar15.com/