Depending on what year and face you're dealing with, PMC can stand for Pan Metal Corporation, Precision Made Cartridges, and maybe one or two other nomes de guerre of the Pusan-based manufacturing concern.
I'm not sure, but I believe that they actually make some of their components here in the US, possibly in CA.
Their Nevada operation definitely assembles components into loaded cartridges. They may even make cases & bullets there as well, but I have no hard recent reports.
Wasn't that helpful? I feel silly with so little info...