I had MAJOR problems with PMC .223 in my AR, but never in my Mini-14.
I have a relatively new Bushmaster, ~300 rounds through it. M193, Winchester, and American Eagle cheapy stuff all shot great, but when I loaded a mag up with the PMC you mention, it would fire, but then subsequent rounds would have a very tough time loading, causing the rifle to jerk as the round didn't quite make it in the chamber, caught on the feed ramp, then made it in. Around 1 out of 4 rounds wouldn't make it in, crunching up inside the receiver and requiring removal.
I posted here, and another guy said he had the same problem with his Bushmaster, saying the copper is of a softer consistency than other manufacturers, and smears itself onto the feed ramp, causing later rounds to "stick" to the feed ramp and cause mis-feeds. If you clean the smeared copper off the feed ramps ~every 20 or so rounds, the problem won't happen.
I just moved my PMC to my Mini-14 only pile of ammo, and feed my "snooty" AR top quality stuff from now on...