Lifesizepotato Shows Off His 10mm HK USP Conversion

Self-proclaimed HK USP fanboy LifeSizePotato takes us on a video tour of his 10mm USP conversion. LifeSizePotato has an epic YouTube channel with some rather rare handguns that make me drool every time he releases a new video. I would sell a kidney to get a chance to go through his collection and fondle all the ultra cool pistols.

This video, he shows us his latest project gun, a Heckler Koch USP .40 S&W that he has converted to fire 10mm. Apparently, this is a conversion that has been floating around the gun world for some time that seems to have eluded me. As a USP fanboy I am nothing short of disappointed in myself for overlooking this mod. Hell, I even had a police trade-in USP .40 a while back that I picked up for a song and sold promptly because I came to my senses and decided adding another caliber to my collection was stupid.

LifeSizePotato says he used a modified STI magazine, an 18 pound recoil spring, and an EFK Fire Dragon barrel reamed out to 10mm by a gunsmith to create the German 10mm powerhouse. Since HK never produced a USP in this caliber it is super cool to see a fan of the platform build something that probably should have been built to begin with.

If you haven’t checked out his YouTube channel, it has some outstanding content. You should probably block off a hour or two to spend drooling over his collection.

Patrick R

Patrick is a Senior Writer for The Firearm Blog and TFBTV Host. He likes guns and has liked shooting guns for as long as he can remember. You can follow Patrick on Instagram @tfbpatrick, Facebook, or contact him by email at

The above post is my opinion and does not reflect the views of any company or organization.


  • A Fascist Corgi

    More companies need to need start making 10mm pistols in order to give the Glock 20 some competition. I’d buy a 10mm USP in a heartbeat.

    • Bigbigpoopi

      I think they’re scared of the gun grenading and getting sued.

      The EAA one would crack from use

      • Roguewriter

        Mine hasn’t.

      • Stan Darsh

        That is only really with the standard Witness 10MM with an overly reduced slide profile and poor heat treatment. The Witness Elite Match and every model above it is good to go.

  • Joe

    I heard about converting Hi Point .40’s, but never thought to apply the concept elsewhere. I wonder what other .40 handguns would work for this conversion?Good stuff TFB!

    • Anonymoose

      It’s been done of .45 P220s before the official factory-made 10mm P220 came around, and a couple people have even done 10mm conversions on Beretta 96s.

      • Gary Kirk

        Really don’t know about using the 96.. That being said, I did mine in 357 sig..

  • MrFN

    The Mateba man himself, he was one of the first youtube channels I really started watching. Fantastic videos, still the only one I know of to do a full run down on the Dardick.

  • Giolli Joker

    As a member of the Mateba Owner’s Club created by lifesizepotato, I definitely appreciate most of his collection.
    I wouldn’t be so confident about shooting a hot-rodded factory handgun, though.

  • Bob

    Or just buy a Glock 20. 29, and 40. I have a 20 and 29 along with a USP 40. The idea of going through all that work… stupid waste of time.

    • Vitsaus

      Some people might want a better gun than a Glock for their 10mm needs.

      • Liberals and Communists trigge

        Should have included a trigger warning in your post.

      • Gus Butts

        With a hammer, a safety/decocker and not being a brick.

        • john huscio

          The USP is the very definition of an ergonomic brick. Glocks are svelte by comparison.

          • Scott Tuttle

            pish! they’re things of beauty!

          • Redfoot

            The plethora of stippling and grip angle conversion shops and the people that use them beg to differ. With that said, good thing there is competition out there-I own both, USP fits me better, Glock 20SF is the most comfortable of all Glocks I have shot out of the box.

    • Patrick R. – Senior Writer

      Heaven forbid we build something as a labor of love. When you have the guns you need, sometimes bringing a pipe dream to life is worth the time.

      • iksnilol

        Same reason I am looking for a 10 year old (or so ) 4×4 Skoda Octavia hatchback (no damned station wagon for me) with gasoline engine… so that I can convert it to rear wheel drive and have basically the realistic car of my dreams.

        • Patrick R. – Senior Writer

          I support this decision because racecar.

          • iksnilol

            Shiny and eternal

            SHINY AND ETERNAL! *crying*

            I found only one for sale in the entirety of Norway, and it was a newer model… and a diesel. Pipe dream indeed.

            But yes, Skodas are great cars. Great trunk space and gas mileage, I’d just like 125-150 hp and rear wheel drive together with the aforementioned trunk space and light weight.

          • Jeff S

            How are you going to convert a Haldex system to RWD? Especially the older Haldex generation – they’re basically 100% FWD until it loses grip.

          • iksnilol

            There’s some mods that can be done.

            Then again it’d be expensive. Might not be necessary though, I mean, I already manage to drift in the turns with FWD without using the handbrake… It’s harder with FWD but I guess more rewarding.

          • A Maze Of Moral Relativism

            Why not just get something from the group B platform that uses the superior Torsen system?

          • iksnilol

            Because I am not a huge fan of Audis and can’t afford a Superb.

            + I like shorter, more nimble.

          • A Mazee Of Moral Relativism

            Quattro and Torsen aren’t mutually exclusive. The B5 Passat uses a Torsen system but keeps the 4motion branding. Conversely the Audi S3 uses a Haldex system despite being an Audi, and an S-series at that.

          • iksnilol

            Oh, you misunderstood. Audis are decent mechanically, but I don’t like them (primarily due to status and weight, they’re heavy suckers and draw attention).

          • Mechanically

            Do I sense some Jalop up in here? If so, I approve.

    • CountryBoy

      Some people do things like this to learn, experience and have something unique. See the term “labor of love”.

      Sure, there are 10mm pistols out there (I have a S&W 1006 I dearly love), but if you like the USP (and I do) and the 10mm caliber, having one in 10mm just makes sense. Eventually the makers may see it being done and consider a factory model.

      Didn’t you ever hotrod your car when you were a teen?

  • iksnilol

    Makes sense considering how big the USP is.

  • Craig Podgurski

    There are dozens of us, DOZENS!

  • Dickie

    I agree and bring back the USP.357Sig & M&P .357Sig

  • LifeSizePotato is one of the best youtube channels out there if you’re into rare pistols.

    • Sam

      It’s cool seeing his channel get some love on here. I’ve been watching his videos for a while. They’re awesome. Definitely opened me up to some pistols I never knew about.

  • Roguewriter

    I would buy a VP10, a USP 10mm, a Steyr L10-A1, a PPQ 10mm, and a IWI Jericho 10mm… If they’d just frickin build them!

    • Jack


  • Cottersay

    Obviously, Mr. Potato knows his stuff, but he really should put a modified magazine sleeve on the bottom of the bare mag…

    • CountryBoy

      Cosmetics… 😉

  • Mike

    Should do a top 10 of guns not already reviewed 2x and in TFB’s collections. …