Wolff Gunsprings offers a WIDE range of hammer spring weights (and recoil spring weights). If you can swap the mainspring on a 1911, you can do it on a USP. It's ONE pin.
The only "short" reset drop-in for the USP is the one from Grayguns. I have it in my fullsize USP 40. I won't say it's bad, but it doesn't actually shorten the reset. It instead turns the reset into more of a 2-stage affair, where the heaviest part of the reset catches in the first half, but the full reset doesn't actually happen until you're into the lighter part. I wouldn't call it a waste of money, but I also don't see myself buying it for my 2nd or 3rd USP.
