This simple, robust +3 fits BOTH the polymer HK USP 15-round mag, and the polymer HK USP Expert 18-round magazine. When attached to the “Expert” mag, the system fits HK’s “Jet Funnel” magwell, and extends the magazine to the maximum length allowed in USPSA’s “Limited” division. Raises the HK to 21+1 in 9mm – one round more than the HK VP9 or P30L! For the everyday USP driver, our +3 adds valuable capacity without making the mag too big to conceal. It’s particularly good as a second magazine, where the extra height conceals more easily, and the extra basepad depth makes the mag easier to reload and seat firmly. Like so many products these days, most HK mags ship with a “hook front” basepad. The protrusion on the front of these magazines has a bad habit of hooking things – especially other magazines in the mag pouch. Our design does away with that, creating a mag that’s easier to manipulate, easier to seat, and less likely to cause trouble on your belt. (Kit does not include the pistol or magwell shown.) Due to US State Department restrictions, we cannot ship this part internationally.
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Well made and well priced. These are the best USP mag extensions on the market.
Picked up one of these to try. Installation was easy and it does fit the rounds as claimed. However, with the factory magazine spring, it will not lock the slide open on empty, even manually cycling the action. Not a big deal. I picked up a replacement 18rd factory spring for the extended factory magazines and then it worked as expected. I think there should either be an extended spring included with the base pad or make it clear in the product description that you need to replace the spring when installing.
I suggest buying the springs for the 18 round mags from hk parts if you are upgrading the 15 round stock mags. If you are upgrading the 18rnd mag to 21 rnds, I recommend buying the 30 round spring (hk parts again) and trimming it 1.5 inches longer then the stock 18 round spring (trim the baseplate side of the spring). Using the spring settups I mentioned above, the slide will lock back, and the mags will run just as well. Without it, it won't lock back on the last round. 100% recommend