MP7 German submachine gun

The MP7 is a German submachine gun manufactured by Heckler & Koch (H&K) and chambered for the 4.6x30mm cartridge. It was designed in conjunction with the new cartridge to meet NATO requirements published in 1989 calling for a personal defense weapon (PDW) class firearm with a greater ability to defeat body armor than current weapons, which are limited due to the use of conventional pistol cartridges. The MP7 went into production in 2001. It is a direct rival to the FN P90, also developed in response to NATO's requirement. The weapon has been revised since its introduction and the current production version is the MP7A1 (see Variants).
The proliferation of high-quality body armor has begun to make guns that fire pistol ammunition (such as HK's earlier MP5 or USP) ineffective. In response to this trend, HK designed the MP7 (along with the brand new UCP, which uses the same ammunition) to penetrate body armor, but small enough to be used in place of either a pistol or a submachine gun.

The primary version of the MP5 submachine gun family is the MP5A2, which is a lightweight, air-cooled, selective fire delayed blowback operated weapon with a roller-locked bolt. The weapon fires from a closed bolt (bolt forward) position and the bolt rigidly engages the barrel extension – a cylindrical component welded to the receiver that the barrel is pinned into. The locking mechanism is of the same design as that used in the G3 rifle. The two-part bolt consists of a bolt head with rollers and a bolt carrier. The heavier bolt carrier lies up against the bolt head when the weapon is ready to fire and inclined planes on the front locking piece lie between the rollers and force them out into recesses in the barrel extension. When fired, expanding propellant gases produced from the burning powder in the cartridge exert rearward pressure on the bolt head transferred through the base of the cartridge case. A portion of these forces is transmitted through the locking rollers projecting from the bolt head, which are cammed inward against the inclined flanks of the locking recesses in the barrel extension and to the angled shoulders of the locking piece. The selected angles of the recesses and the incline on the locking piece produce a velocity ratio of about 4:1 between the bolt carrier and the bolt head. This results in a calculated delay, allowing the projectile to exit the barrel and gas pressure to drop to a safe level before the bolt is unlocked and the chamber opened. The delay results from the amount of time it takes for enough recoil energy to be transferred through to the bolt carrier in a sufficient quantity for it to be driven to the rear against the force of inertia of the bolt carrier and the forward pressure exerted against the bolt by the recoil spring. As the rollers are forced inward they displace the locking piece and propel the bolt carrier to the rear. The bolt carrier's rearward velocity is four times that of the bolt head since the bolt remains locked for a short period of time after the initial recoil impulse. After the bolt carrier has traveled rearward 4 mm, the locking piece is withdrawn fully from the bolt head and the locking rollers are compressed into the bolt head (which moves only 1 mm). Only once the locking rollers are fully cammed into the bolt head can the entire bolt group begin its rearward movement in the receiver, breaking the seal in the chamber and repeating the feeding cycle.