There are umpteen threads about the quality of the Norinco 5.56. Do a search. In a nutshell, the majority have shot thousands of rounds with no problem and also reload the brass if you're into that. At 25 cents/rd, who needs to waste time and effort reloading?
Non-corrosive. And there's a thread somewhere with pics from CanAm to prove it.
PMC is better quality with a (MUCH) higher price tag to match. For the money, Norinco 5.56 can't be beat.