I had purchased case lots (1000 or more rounds) of Maine Cartridge, PMP commercial, Q3131A, IMI M193 and Federal XM193.  I was curious if mil-spec ammo really was loaded much hotter than commercial .223.  I picked up a box of yellow box UMC to serve as my control .223 round.  All rounds tested were 55gr FMJ.  Gun was a 16" J&T upper, non-chrome.  Chrono was placed about 15' from the muzzle.  Please, no comments about mil-spec distance; I was only interested in the comparison.  The loads were shot one after another, giving the barrel about 10 minutes between ammo brands to cool some.  The posted velocities are averages of 5 shots.

Maine Cartridge  2661 fps
Q3131A  3030fps
PMP  2791fps
UMC  2908fps
XM193  3007fps
IMI  3000fps

I will pass on PMP and MC in the future.  But, if I see some UMC go cheaper than Q3131A, IMI, or XM193, I will be all over it.