DC as I thought about your problem, it seemed as if the cartridges are not riding up the face of the slide. I would bet you have either some sort of burr or roughness on the front of the slide face or extractor. The second possibiliy is your load is just barely enough for a clean gun. Increasing your load to the middle of the range for 231 powder might be all it takes.
I set my OAL for the 45 by trial and error for each bullet type. I disassemble the gun then drop a loaded round into the chamber. I adjust the seating die so the loaded round is just sightly deeper than flush with the hood of the barrel. I am not sure if this will be true with your USP. Good luck.