Loose barrel would explain why I ran out of elevation adjustment with the rear sight. It's shooting over a foot low at 25 yards. If I keep it I could shave a bit off the front...or just buy an Eotech and be done with it.
Also, all you "UMP" owners out there, be careful if you perform that magazine feed lip mod. I think I got a bit too rambunctious on one of the mags. I removed a wee bit too much material and fear I may have ruined the mag.