PMC has been good stuff in my opinion. I have went through a case of their .223, and probably another case of 9 mm, 40 SW and 45 ACP combined and have had no problems or complaints, and like everyone else has said always went bang.
I have shot quite a bit of PMC in 9mm, .38, .357, .45 acp, and a little in .44 mag and .223. All good.
UMC, whose only connection, I think, is that it has three letters in its name, is indeed a different story. All I have tried is yellow box stuff, and it is weak. Some of my autos won't cycle it reliably, while others will. I bought a bunch of 9mm at Bass Pro when it was about $80/1000. Still have most of it. I use it on the range with my 9mm pistols that like it. My P-89 eats anything, as do my Star BMs and one or two others. The P-38 hates it, and it digests everything else just fine. The rest of the 9mm herd experiences intermittent failures, including my Glock 17. CB