The MP5, basically, is no more than the scaled-down version of the Heckler-Koch G3 battle rifle. It shares the same basic design with stamped steel receiver and the same roller-delayed blowback action, derived from the post-war CETME rifles. The trigger units are hinged to the receiver and are now available with various fire mode options, including 2 (Safe, Semi-auto), 3 (Safe, Semi, Full Auto) or 4 (Safe, Semi, Limited burst of 2 or 3 rounds, Full auto) position levers, ambidextrous or not, and marked with letters, digits or icons. The MP5 is always fired from closed bolt for improved accuracy, but this limits the amount of sustained fire due to the barrel overheating and resulting cook-off problems. To avoid this, MP5 cocking handle could be locked in the rear position in the special slot, leaving the bolt in the open position, with no cartridge in the chamber. To commence the fire one must simply release the cocking handle from its notch and then pull the trigger. Modern MP5 submachine guns are equipped with three-lug quick detachable silencer mounts on the barrel. Sights are similar to other HK models, and consists of the front hooded post sight and the adjustable for windage and elevation drum-type diopter rear sight. Special quick-detachable clamp mounts allows for installation of night, optical and red-dot sights if required. Standard magazine capacity is 30 rounds, but shorter 15 rounds magazines are available. Special versions were developed and manufactured in limited numbers during 1980s-90s for the US Law Enforcement market, chambered for more powerful 10mm Auto (10x25mm) and .40S&W (10x22mm) ammunition. These guns can be easily distinguished from more common 9mm models by straight box 30 rounds magazines, made from plastic.
While all of MP5 can be fitted with silencers, there also a dedicated silenced version of MP5, called MP5SD2 or SD3 (depending on the stock type). This version is equipped with non detachable integral silencer, and the vented barrel, to reduce the bullet muzzle velocity down below the speed of sound. The MP5SD is intended to fire standard 9mm ammunition, not the special subsonic one.
Semi-automatic only versions of the MP-5 were once made for civilian market under the designation of HK-94, some with longer, 16 inch (406 mm) barrels, to conform with US laws. There also is an US company, called Special Weapons LLC, that is manufacturing semi-automatic, civilian MP5 clones in various pistol calibers, including the .45ACP.