The HK45 is what HK built after learning from the USP. It started as HK's submission for the Joint Combat Pistol program (the military's attempt to replace the Beretta M9 with a .45 ACP), and although that program died, the HK45 survived as a production gun. The grip is the biggest improvement over the USP. Interchangeable backstraps and a slimmer profile make the HK45 fit a wider range of hand sizes, where the USP's thicker grip has always been a complaint among shooters with smaller hands.

At 31.2 oz with a 4.46-inch barrel and 8.03-inch overall length, the HK45 is close in size to the USP 45 (31.3 oz, 4.41-inch barrel, 7.91 inches). Both hold 10+1 rounds with the same DA/SA trigger system and safety/decocker. The HK45 runs a 4.5 lb single-action pull versus the USP's 4.8 lbs. The HK45 uses a standard Picatinny rail instead of the USP's proprietary mount, which opens up the full range of weapon lights.

For anyone choosing between HK .45 ACPs: the HK45 accepts the same barrel locking system and recoil reduction setup as the USP, but the ergonomics are a generation newer. If you plan to mount a light, the Picatinny rail alone makes the HK45 the better choice. Break the gun down before buying if possible, because the grip difference between the HK45 and USP is the kind of thing you feel immediately.