The USP (Universale Selbstladepistole or “universal self-loading pistol”) is a semi-automatic pistol developed in Germany by Heckler & Koch GmbH (H&K) of Oberndorf am Neckar as a replacement for the P7 series of handguns.
The USP 40 is a semi-automatic pistol with a mechanically locked breech using the short recoil method of operation. This rather conventional lock-up system has a large rectangular lug over the barrel’s chamber that rides into and engages the ejection port cut-out in the slide. When a cartridge is fired, pressures generated by the ignited powder drive the cartridge casing back against the breech face on the slide, driving back both the barrel and slide as they remain locked together in the manner described above. After 3 mm (0.12 in) of unrestricted rearward travel, the projectile has left the barrel and gas pressures have dropped to a safe level. A shaped lug on the underside of the barrel chamber comes into contact with a hooked locking block at the end of the steel recoil spring guide rod, lowering the rear end of the barrel and stopping the barrel’s rearward movement. The recoil spring assembly is held in place by the slide stop lever’s axis pin and a round cut-out at the front of the slide. For enhanced reliability in high-dust environments, the locking surface on the front top of the barrel’s locking lug is tapered with a forward slope. This tapered surface produces a camming action which assists in positive lock-up in the presence of heavy fouling and debris.
One of the most significant features of the USP is the mechanical recoil reduction system. This system is incorporated into the recoil spring assembly, located below the barrel and consists of a heavy, captive coil spring around the guide rod. Designed primarily to buffer the slide and barrel and reduce recoil effects on the pistol components, the system also lowers the recoil forces felt by the shooter up to 30%. The USP recoil reduction system is insensitive to ammunition types and does not require adjustment or maintenance. It functions effectively in all USP models. Using this same recoil reduction system, one of the related H&K Mk 23 .45 ACP pistols fired more than 30,000 high pressure +P cartridges and 6,000 proof loads without damage or excessive wear to any major components. Abuse and function-testing of USPs have seen more than 20,000 rounds of .40 S&W fired without a component failure. Milspec environmental tests were conducted in high and low temperatures, in mud, immersed in water and in salt spray. In one particular test, a bullet was deliberately lodged in the barrel and another bullet was fired to clear the obstruction. The barrel was successfully cleared with only minor structural deformation and continued to produce consistent groups when test fired for accuracy.
Major metal components on both the USP and Special Operations Pistol are corrosion-resistant. Outside metal surfaces,
such as the steel slide are protected by a proprietary “Hostile Environment” nitride finish. Internal metal parts, such as springs, are coated with a Dow Corning anti-corrosion chemical to reduce friction and wear.
The USP is composed of a total of 54 parts and is broken down into 7 major components for maintenance and cleaning: the barrel, slide, recoil spring, recoil spring guide rod, the frame, slide stop and magazine. This is done by retracting the slide back to align the slide stop axis pin with the disassembly notch on the left side of the slide and withdrawing the axis pin.