Don't own a USP, everytime I've looked at one I've bought something else. I do own a Mark23 and a P99. The bad thing about the P99 in .40 is that it was designed to be a 9mm, an excellant gun. You always loose something when you turn a 9mm into a .40. No USP(full or compact) fits my hand as well as the P99. I didn't have to search for preban mags, lots of 16 round mags out there. I can't imagine getting parts for a Walther could be any harder than getting parts for an HK. If your friend does get a Walther in .40 it MUST have 3 German proof marks, R. front of frame, R. rear of slide, and barrel. If the proof mark is not on the slide it was one of 3000 made by s&w and there WILL be problems.