The MP5 is a 9 mm submachine gun of German design, developed in the 1960s by a team of engineers from the West German arms manufacturer Heckler & Koch GmbH (H&K) of Oberndorf am Neckar. The company, motivated by the success of the G3 automatic rifle, developed a family of small arms consisting of four types of firearms (all based on a common G3 design layout and operating principle), where the first type was chambered in 7.62x51mm NATO, the second – using the 7.62x39mm M43 round, third – the intermediate 5.56x45mm NATO caliber and the fourth type – chambering the 9x19mm Parabellum pistol cartridge. The MP5 (short for Maschinenpistole 5) was created within the fourth group of firearms, initially known as the HK54.
Work on the MP5 began in 1964 and scarcely two years later it was adopted by the German Federal Police, border guard and army special forces. It is currently used by the armed forces and law enforcement units of over 40 different countries. The submachine guns are manufactured under license in several nations including: Greece (Hellenic Arms Industry), Iran (Defense Industries Organization), Mexico (SEDENA), Pakistan (Pakistan Ordnance Factories), Sudan (Military Industry Corporation), Turkey (MKEK), and the United Kingdom (initially at Royal Ordnance, later diverted to Heckler & Koch Great Britain). The MP5 remains one of the most widely deployed of all current submachine guns and has been developed into a family with numerous variants.
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.
Since the 9x19mm Parabellum cartridge is relatively “weak”, the bolt does not have an anti-bounce device like the G3, but instead the bolt carrier contains tungsten granules that prevent the bolt group from bouncing back after impacting the barrel extension. The weapon has a fluted chamber that enhances extraction reliability by bleeding gases backwards into the shallow flutes running along the length of the chamber to prevent the cartridge case from expanding and sticking to the chamber walls (since the bolt is opened under relatively high barrel pressure). The MP5 employs a push-type extraction, instead of the more conventional pull-type extraction. The cartridge case is pushed from the chamber of the weapon by residual gas pressure. A spring extractor is installed inside the bolt head and holds the case securely until it strikes the ejector arm and is thrown out of the ejection port to the right of the receiver. The lever-type ejector is located inside the trigger housing (activated by the movement of the recoiling bolt).
The non-reciprocating cocking handle is located above the handguard and protrudes from the cocking handle tube (often mistaken for a gas cylinder) at approx. a 45° angle. This rigid control is attached to a tubular piece within the cocking lever housing called the cocking lever support, which in turn, makes contact with the forward extension of the bolt group. It is not however connected to the bolt carrier and therefore cannot be used as a forward assist to fully seat the bolt group. The cocking handle is held in a forward position by a spring detent located in the front end of the cocking lever support which engages in the cocking lever housing. The lever is locked back by pulling it fully to the rear and rotating it slightly clockwise where it can be hooked into an indent in the cocking lever tube. The cocking lever is generally operated with the non-firing hand, allowing the shooting hand to remain on the pistol grip.
The MP5 has a hammer firing mechanism. The trigger group is housed inside an interchangeable polymer trigger module (with an integrated pistol grip) and equipped with a 3-position fire mode selector that is also the manual safety toggle (selector lever in the “S” or Sicher position in white – weapon safe, “E” or Einzelfeuer in red – single fire, “F”, Feuerstoß also marked in red – continuous fire). The SEF symbols appear on both sides of the plastic trigger group. The selector lever is actuated with the thumb of the shooting hand and is located only on the left side of the of the original SEF trigger group or on both sides of the ambidextrous trigger groups. The safety/selector is rotated into the various firing settings or safety position by depressing the tail end of the lever. Tactile clicks (stops) are present at each position to provide a positive stop and prevent inadvertent rotation. The "safe" setting disables the trigger by blocking the hammer release with a solid section of the safety axle located inside the trigger housing.
The first MP5 models used a double-column straight box magazine, but since 1977, slightly curved, steel magazines are used with a 15-round capacity (weighing 0.12 kg) or a 30-round capacity (0.17 kg empty).
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.
The MP5A2 and MP5A3 submachine guns are also available with optional 4-position trigger groups; such equipped weapons are known as the MP5A4 and MP5A5 (respectively). The trigger groups are marked with bullet pictograms rather than letters or numbers (each symbol represents the number of bullets that will be fired when the trigger is pulled and held rearward with a full magazine inserted in the weapon) and are fully ambidextrous (the selector lever is present on each side of the trigger housing). The additional, fourth setting of the fire selector enables a two or three-shot burst firing mode. H&K also offers dedicated training variants of these weapons, designated MP5A4PT and MP5A5PT (PT - Plastic Training), modified to fire a plastic 9x19mm PT training cartridge produced by Dynamit Nobel of Germany. These weapons operate like the standard MP5 but have a floating chamber and the bolt lacks both rollers to function properly when firing the lighter plastic projectiles. To help identify these weapons blue dots were painted on their cocking handles and additional lettering provided. The PT variant can be configured with various buttstocks and trigger groups and was developed for the West German Police and Border Guard.
Thanks to the modular design of the MP5, particularly the trigger groups, a large number of configurations are available to meet the user’s individual requirements. Currently offered are the following trigger groups: three-position selector/safety (settings: safe, semiautomatic and a 2 or 3-round burst; selector lever is ambidextrous and its settings are marked with symbols); four-position fire safety selector (settings: weapon safe, single fire, 2-round burst, full auto; ambidextrous selector; selector settings marked with pictograms); two-position fire control group (positions: “S” – weapon safe, “E” – single fire only; selector lever located on the left side of the trigger housing) and a three-position fire selector/safety group - the so called “Navy” trigger (settings: weapon safe, semi-automatic, fully automatic fire; ambidextrous selector lever/safety; selector settings marked with bullet symbols).
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 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 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 barrel has 30 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.
The MP5SD is produced exclusively by H&K in several versions: the MP5SD1 and MP5SD4 (both have a receiver end cap instead of a buttstock), MP5SD2 and MP5SD5 (equipped with a fixed synthetic buttstock) and the MP5SD3 and MP5SD6 (fitted with a collapsible metal stock). The MP5SD1, MP5SD2 and MP5SD3 use a standard "SEF" trigger group (from the MP5A2 and MP5A3), while the MP5SD4, MP5SD5 and MP5SD6 – a trigger module with a mechanically limited 3-round burst mode and ambidextrous selector controls (from the MP5A4 and MP5A5). A suppressed version was also produced for the U.S. Navy - designated the MP5SD-N, which is a version of the MP5SD3 with a retractable metal stock, front sight post with tritium-illuminated dot and a stainless steel suppressor. This model has a modified cocking handle support to account for the slightly larger outside diameter of the suppressor. The design of the suppressor allows the weapon to be fired with water inside, should water enter the device during operation in or near water.
In 1976 a shortened version of the MP5A2 was introduced; the MP5K (K – Kurz) was designed with clandestine operations and special services in mind primarily for close quarters battle. This submachine gun does not have a shoulder stock (the receiver end was covered with a flat cover), and the bolt and receiver were shortened at the rear. The resultant lighter bolt led to a higher rate of fire than the standard MP5. The barrel, cocking handle and its cover were shortened and a vertical foregrip was used to replace the standard handguard. The barrel ends at the base of the foresight, which prevents the use of any sort of muzzle device.
MP5K submachine guns are produced (by HK and under license in Iran and Turkey) in four different versions: the MP5K, MP5KA4, MP5KA1, MP5KA5, where the first two variants have adjustable, open-type iron sights (with a notched rotary drum), and the two remaining variants - fixed open sights, however the front sight post was changed and a notch was cut into the receiver top cover. The MP5K retained the capability to use optical sights through the use of an adapter.
A civilian semiautomatic derivative of MP5K known as the SP89 was produced that had a foregrip with a muzzle guard in place of the vertical grip.
In 1991 a further variant of the MP5K was developed, designated the MP5K-PDW (PDW – Personal Defense Weapon) that retained the compact dimensions of the MP5K but restored the fire handling characteristics of the full-size MP5A2. The MP5K-PDW uses a side-folding synthetic shoulder stock (made by the US company Choate), a “Navy” trigger group, a front sight post with a built-in tritium insert and a slightly lengthened threaded, three-lug barrel (analogous to the MP5-N). The stock can be removed and replaced with a receiver endplate; a rotary drum with apertures from the MP5A2 can also be used.
1991 saw the introduction of the nearly identical MP5/10 (chambered in 10mm Auto) and MP5/40 (chambered for the .40 S&W cartridge) submachine guns, which are based on the MP5A4 and MP5A5. These weapons were assembled in fixed and retractable stock configurations (without a separate designation) and are fed from translucent 30-round polymer box magazines. These weapons also include a bolt hold-open device, which captures the bolt group in its rear position after expending the last cartridge from the magazine. The bolt is then released by pressing a lever positioned on the left side of the receiver. Both weapons use a barrel with 6 right-hand grooves and a 380 mm (1:15 in) twist rate, and like the MP5-N, both have a 3-lugged muzzle device and a tritium-illuminated front sight aiming dot.