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Discussion Starter · #1 · (Edited)
I’m late with this, but on July 31 I took my 10mm USP conversion to the range for the first time. The USP was a trade-in from a private security firm with an AB date code and in good shape: solid internals, slide and frame show some holster wear but the night sights have some life left in them. The gun was relatively inexpensive (for a USP, at least) so I didn’t feel quite as bad modifying it. I came as a V3 and I changed it to a V1, then I bought a threaded barrel from Michael’s Machines and had been intending to have the ejection port opened up to allow unfired rounds to be ejected. I was been in touch with Mark Housel over at L&M Precision, who is a great guy: he was super helpful, responded very quickly to all of my emails, and was willing to do the work for a fair price. I never got around to sending the pistol to him and just decided to take it to the range anyway after I made some modifications over the course of a few months at home.

In order to reduce stress on the frame, I installed a new tactical guide rod assembly and added a 20 lb. recoil spring from Wolff. I ever-so-lightly sanded the front of the magazine well to allow a HK45 magazine to be inserted and removed more easily – the larger magazines drop free some of the time and would probably do so more consistently if I treated them with dry lube. I also installed an extended magazine release lever from HK Parts, and that required some gentle sanding to avoid catching on the larger HK 45 magazine. I didn’t want to sand so much material away from the magazine well that the 40 S&W magazine would wobble around and I don’t notice any difference with the factory magazine inserted. There is a little bit of play, but not noticeably more than there was when I bought the thing, and the original magazine still functions flawlessly. I didn't remove any material from the back of the magazine well because I didn't want the HK45 magazine to be any closer to the sear actuator latch than it already is.

The HK45 magazines obviously aren’t a perfect mate for the USP without some modification. The foot at the front of the magazine’s floor plate was annoying, so I cut it off and sanded the floor plate smooth so it sits flush with the grip. However, because the HK45 magazine is longer than the USP’s grip it is possible to over-insert the magazine which will drag on the slide. To address this, I added a jet funnel and sanded down a spare floor plate and adhered it to the top of the original floor plate with Loctite. The larger floor plate now contacts the jet funnel as the magazine release lever catches and prevents over-insertion of the magazine. To get the slide to lock back on an empty magazine all I had to do was Dremel the left-side feed lip, removing maybe a millimeter or two of material.

After the recent run on ammo, I bought the last two boxes of PMC Bronze in town and headed to the range. Initially, the rounds tended to “nose up” in the chamber, but with pliers I closed the feed lips a bit and that pretty much solved the issue. After that, the slide locked back a few times when there were still rounds in the magazine and I’m not entirely sure why that was happening (please let me know if you have any ideas). Other than that, the USP ran quite well! The PMC (200 gr.) ammo isn’t the hottest stuff out there, but even with the 20 lb. recoil spring, the slide never returned to battery without chambering a round. It’s really a surprisingly soft shooter, I had run through 500 rounds of 9mm in the morning so I wasn’t fresh but I still didn’t get any of the wrist-shocking sensation I’ve seen people write about.

It was a fun project, and there are still some wrinkles to iron out, but I feel like I accomplished my goal of shooting 10mm through a USP. Since the range trip, I’ve kind of lost interest as my gaze has drifted to other HK items I’d like to add to the collection. Huge thanks to @waz0wski for helping me along with advice through virtually every stage of this project. Thanks to @chune for organizing the group-buy and to @hk21man for making the barrels. I attribute a the success of my efforts to this forum and the helpful, informational posts by folks who have made similar conversions - while I tried some things I hadn't seen written about before (e.g. custom floor plates), I was able to avoid a lot of trial and error from reading these forums. I hope this post will help those who are interested in attempting a similar conversion. If you are patient and looking for a project, I’d recommend this to anybody who is a fan of the USP and the 10mm round.

USP10.JPG USP10_mag.JPG
Edit: removed a superfluous return
 

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Discussion Starter · #3 · (Edited)
Thanks, Tony! It was a fun project and I am eager to move forward with the next steps

Edit: I had no idea what sandbagging was or that it was such an issue on these forums. I've been a long time lurker and am just eager to exchange equipment with other enthusiasts - my apologies that this post (in its original form) did not reflect that.
 
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