I have not seen anyone attempt a 10mm USP the way I did this one.

I bought a .40 EFK barrel, I reamed it to 10mm and polished barrel feed ramps etc.- as has been done
I put in the 18lb recoil spring too.
Took the .40 slide assembly and put it on a USP .45 frame.
I used the USP .45 mags which feed 10mm fine after I adjusted the feed lips
So the slide lock functions perfectly.
I opened up the ejection port, so it no ejects live rounds as normal

I had some feeding issues as the EFK barrel had abrupt/sharp edges; but I believe I have worked thru them
The .45 frame is about 2-3mm longer at the barrel end, but isn't noticable; and after I test fire again and validate function; I will sell the .40 frame off;
Buy a .45 USP and sell that slide off....
Pics to be added shortly




[attachment deleted by admin]

Sounds like a cool project you have there Scu!   

With your success it sure makes one wonder why HK has not offered a 10 in the USP?

Looks cool

Just curious, will this set-up eject a loaded round from the chamber.  The other conversion I saw would not.

yes
I opened the ejection port

If this feeds better (I had a few hickups feeding at the 3rd range test) then this is pretty much a 100% functioning all HK (except Barrel and spring) gun

It should be identical to shooting it in .40 or .45;

Not sure how I was the first to come up with this idea and test it; but it seems to work fine

I did have once that the hammer did not stay back (but I am sure that can be rectified with spring swap if needed)

Any pics of where/how you opened up that port would be very appreciated.  This has been the sticking point for me looking hard at this conversion.

I'll be interested in seeing that as well.

I have pics but they are too large to upload. I will workj on it tomorrow