MP5

The sighting arrangement on the MP5 takes advantage of the natural ability of the eye and brain to easily align concentric circles (circles all having a common center). The mechanically adjustable iron sights (closed type) consist of a rotating rear diopter drum and a front post installed in a hooded ring. The rear sight is adjustable for both windage and elevation with the use of a special tool; the drum provides four different apertures of varying width used for firing at 25, 50, 75 and 100 m. However, adjusting the rear drum does not change the elevation or bullet strike of the rounds since the MP5 uses pistol cartridges, which share a similar point of impact between 25 and 100 m when zeroed at 25 m. The receiver housing has notches that permit the attachment of a standard H&K quick-detachable scope mount (also used with the G3, HK33 and G3SG/1) that can be used to mount daytime optical sights (telescopic 4x24), night sights or a halogen flashlight. It can also be used with reflex sights and laser pointers. The mount features two spring-actuated bolts, positioned along the base of the mount, which exert pressure on the receiver to hold the mount in the same position at all times assuring zero retention. All versions of the quick-detachable scope mount provide a sighting tunnel through the mount so that the shooter can continue to use the fixed iron sights with the scope mount attached to the top of the receiver.
The fixed, free floating, cold hammer-forged barrel has 6 right-hand grooves with a 1 in 250 mm (1:10 in) rifling twist rate and is pressed and pinned into the receiver. Three lugs are provided at the muzzle that are used to work with certain muzzle devices made by Heckler & Koch, including: a slotted flash suppressor, blank firing attachment (marked with a red painted band denoting use with blank ammunition only), an adaptor for launching rifle grenades (for use with rifle-style grenades with an inside diameter of 22 mm using a special grenade launching cartridge) and a cup-type attachment used to launch tear gas grenades.
The MP5A2 has a fixed stock (made of a synthetic polymer), whereas the compact MP5A3 has a retractable metal stock.
Included with the MP5A2 and MP5A3 are: sling, cleaning kit, quick-loading device and a clamp which holds two magazines. As an option, tritium-illuminated sights are also available (used for firing in low-level lighting conditions) as well as sound suppressors from several aftermarket manufacturers.
In the early 1970s HK introduced a conversion kit for the MP5 that enables it to use sporting ammunition (.22 LR). This unit consists of a barrel insert, a bolt group and two 20-round magazines. This modification reduces the cyclic rate to 650 rounds/min.