The Heckler & Koch Ultimate Combat Pistol (HK UCP), also known as the HK P46, was a double action, semi-automatic handgun developed under commission for the German Bundeswehr.
The UCP is the companion side arm to the HK MP7 submachine gun, using the same 4.6x30mm bottlenecked cartridge (see internal ballistics). The 4.6x30mm round is a direct competitor to the 5.7x28mm by Fabrique Nationale de Herstal (FN). As such, the UCP is a direct competitor to the FN Five-seven pistol. Both have armor-piercing capabilities and a low recoil in comparison to other commonly used military handgun cartridges, such as the 9x19mm Parabellum or .45 ACP.
The UCP operates on the delayed-blowback operating principle. The external design of the UCP appears to be borrowed from the HK P2000 pistol, and includes ambidextrous controls, interchangeable backstraps, and a MIL-STD-1913 Picatinny-type rail system for the attachment of accessories. Like the USP and P2000 series of pistols, the trigger mechanism is reported to be modular and capable of different configurations. The UCP is designed to accept an extended, threaded barrel capable of accepting the attachment of a sound suppressor made by Brügger & Thomet. Initial speculation that the UCP will accept 40-round MP7 magazines appears to be false.
The design remains in the prototype phase as of 2006[update], and has been reported as entering limited trials with the Bundeswehr.
In July 2009, HK USA's president, Wayne Webber, indicated that the UCP project has been cancelled because "HK felt it did not provide adequate ballistics in handgun form."