mp5

A variant with the last trigger group designated the MP5-N (N – Navy) was developed in 1986 for the United States Navy Special Warfare community. This model has a collapsible stock, a tritium-illuminated front sight post and a 225 mm (8.9 in) threaded barrel for use with a stainless steel sound suppressor made by KAC (when suppressed subsonic ammunition is used). The MP5SFA2 (SF - single-fire) is the same as the MP5A2 but is fitted with an ambidextrous semi-automatic only trigger group. Versions delivered after December 1991 are assembled with select-fire bolt carriers allowing fully automatic operation when used with the appropriate trigger module. Developed in 1986 in response to the American FBI solicitation for "9 mm Single-fire Carbines". The MP5SFA3 features a retractable metal stock. The two-position trigger unit was also used in the single-fire HK94 carbine that was produced specifically for the civilian market with a 420 mm (16.5 in) barrel. In 1974 H&K initiated design work on a sound-suppressed variant of the MP5, designated the MP5SD (SD – Schalldämpfer or "suppressed"), which features an integral but detachable aluminum sound suppressor and a lightweight bolt. The weapon's 146 mm (5.7 in) barrel has 30 2.5 mm (0.1 in) ports drilled forward of the chamber through which escaping gases are diverted to the surrounding sealed tubular casing that is screwed on to threading on the barrel’s external surface just prior to the ported segment. The suppressor itself is divided into two stages; the initial segment surrounding the ported barrel serves as an expansion chamber for the propellant gases, reducing gas pressure to slow down the acceleration of the projectile. The second, decompression stage occupies the remaining length of the suppressor tube and contains a stamped metal helix separator with several compartments which increase the gas volume and decrease its temperature, deflecting the gases as they exit the muzzle, so muffling the exit report. The bullet leaves the muzzle at subsonic velocity, so it does not generate a sonic shock wave in flight. As a result of reducing the barrel’s length and venting propellant gases into the suppressor, the bullet’s muzzle velocity was lowered anywhere from 16% to 26% (depending on the ammunition used) while maintaining the weapon’s automation and reliability. The weapon was designed to be used with standard supersonic ammunition with the suppressor on at all times.