Thanks, Mike, but this is why I was hoping for more definitive info. The USP 9 was built on a .40 frame. In others words, HK designed a .40 cal pistol then changed parts to accomodate the 9mm. I'm thinking that at most I would need to change would be the barrel, slide and magazines but was hoping someone had some first-hand knowledge.
I'm actually hoping because HK built this as a .40 the slide would not need be changed. Not sure on how the breech face and extractor would work.
Even if the slide was nearly/exactly the same weight you still have
the breechface problem. A 9mm slide does not have a wide enough
breechface to accommodate the .40 S+W casehead. I know for a
fact that the USP9 breechface is indeed only cut for 9mm casehead.
I don't know of any 9mm handgun that has breechface that's too wide, in general. )
I agree that the -bare frames- are probably -EXACTLY- the same, but
then things get funny from there on out. If the ejectors are different,
you're essentially screwed because on a USP the ejector is pretty much
molded into the frame. (At least the last time I detail stripped one of
my USPs, I was unable to remove that part, as it seems like its part of
the frame. )
Remember that, -anything- is possible, it's just a matter of the lengths
you would go through to do it.
-Mike