Type Assault rifle
Place of origin West Germany
Designer Heckler & Koch
Variants Assault Rifle, Light Machine Gun (LMG11), Personal Defence Weapon (G11 PDW)
Weight 3.6 kg (8.0 lb) empty, 4.3 kg (9.5 lb) loaded
Length 750 mm (29.5 in)
Barrel length 540 mm (155 mm per twist)
Cartridge 4.73x33 mm caseless ammunition
bullet mass 3.25 g
Rate of fire 550 rounds/min full auto, 2200 rounds/min 3 round burst
Muzzle velocity Approx. 930 m/s (3,050 ft/s)
Effective range 400 m
Feed system 45 or 50-round detachable box magazine
Sights Integrated optical sight
The Heckler & Koch G11 is a non-production prototype assault rifle developed during the 1970s and 1980s by Gesellschaft für Hülsenlose Gewehrsysteme (GSHG) (German for "Corporation for Caseless Rifle Systems"), a conglomeration of companies headed by firearm manufacturer Heckler & Koch (mechanical engineering and weapon design), Dynamit Nobel (propellant composition and projectile design), and Hensoldt Wetzlar (target identification and optic systems). The rifle is noted for its use of caseless ammunition.
It was primarily a project of West Germany, though it was also of significance to the other NATO countries as well. In particular, versions of the G11 were included in the U.S. Advanced Combat Rifle program.
The weapon uses a 4.73x33 mm caseless ammunition, with the propellant shaped into blocks.  The ammunition is also designated as 4.92 mm because in US Military trials, a non-standard groove-groove measure of the rifling was employed, rather than land-land. The barrel chamber is 4.73 mm, and the bullet is compressed to that size when fired. The 4.73 mm round is half the weight and 40% the size by volume of the 5.56x45mm NATO round used in assault rifles. The 4.73 mm round also has similar ballistics to a 5.56 mm round, but the 4.73 mm is much less likely to tumble when hitting or penetrating a target, and thus not as lethal. It is not clear to what extent the round would fragment, which could also make it more lethal. (See terminal ballistics)
The design principle was to fire multi-round bursts with a higher degree of hit probability than is possible with earlier rifles. The weapon itself has three firing modes: semi-auto, full-auto at 400-600 rounds per minute, and three-round burst at 2000 cyclic rounds per minute, which is approximately 36 rounds per second. The loading and feed mechanism is physically very complicated but exceptionally fast and reliable. Rounds are held vertically from above the barrel. The firing cycle process is roughly:
1. As the cocking handle on the side is rotated clockwise by the weapon operator:
2. A round is dropped into the revolving chamber vertically (a loading piston assists this process).
3. The chamber rotates 90° until it is lined up with the barrel. This completes the chambering of the round and cocking of the firing pin.
4. When the trigger is pulled, a firing pin ignites the primer, which then ignites a powder booster charge that pushes the bullet into the barrel. Then the solid lump of propellant ignites, accelerating the bullet out of the barrel.
5. The chamber then rotates back to its original position until it is lined up with the feed mechanism and the process repeats.
A conventional assault rifle has about seven steps in its cycle, but because the G11 uses caseless ammunition there are no extraction and ejection steps. Also, due to the G11 having no loading bolt, there are no locking and unlocking steps either. If a round fails to fire, the rifle can be manually chambered by twisting the cocking handle counterclockwise. This pushes the dud out an emergency ejection port on the bottom of the rifle and loads the next round.
The recoil in the three-round burst is not felt by the weapon's user until after the third round has left the chamber. This is accomplished by having the barrel and feeding mechanism "float" within the rifle casing. When the bullets are fired, the barrel and mechanism recoils back freely several inches and only when it hits the plate at the back of the rifle does the user feel the recoil. During this transit time the rifle loads and fires 3 rounds. When the barrel and mechanism reaches the back, springs push it forward into its normal position. When firing in semi-auto and full auto modes, the rifle only loads and fires one round per transit of the barrel, cutting the rate of fire to a controllable one-third of its maximum rate.
The internal workings of the rifle were rather complex compared to those of some earlier designs, with the guts being compared to the inside of a compact clock. The number of hours of maintenance required for the G11 as compared to other designs is not clear, especially since the impact of the powder used in the caseless ammo remains unknown. Designers claimed that because there was no ejection cycle the internal mechanisms would have little chance to get exposed to external dust, dirt and sand and this would supposedly reduce the need for cleaning.
 Ammunition cook-off and shape
The 4.73x33mm caseless ammunition used in the G11 rifle.
Premature ignition of ammunition by heat in the firing chamber, known as cook-off, was a major problem with early prototypes of the G11. Normally, when a bullet is fed into a chamber its casing prevents its powder from igniting until its shock-sensitive primer is struck by a firing pin. When the gunpowder is ignited, the casing absorbs much of the heat resulting from the ignition, thereby reducing the heat that the chamber would otherwise be exposed to. Semi-automatic and fully automatic weapons usually eject the casing quickly enough to keep it from overheating the chamber at a normal rate of fire. As a result of doing away with casings, the G11 became a safety hazard and had to be withdrawn from the 1979 NATO trials. The high rate of fire and lack of casings made cook-off a big problem.
To solve this, Dynamit Nobel redesigned the cartridge to use a new High Ignition Temperature Propellant (HITP). The cook-off problem was supposedly fixed, or at least reduced, by using a denatured hexogen propellant with a special binder and coating for the ammunition that increased the spontaneous ignition temperature to 100 °C (212 °F) above that of standard, nitrocellulose propellant.
An interesting feature of the new round was its unconventional shape. Most round casings are cylindrical to allow for easy ejection. However, the redesigned cartridge was molded into a squared, box-like shape. This allowed the 50-round magazine to carry the maximum amount of propellant in a minimum of space, since the wasted spaces between rounds that accompanies the use of round cartridges was eliminated.
The issue of heat removal from caseless firing weapons as well as methods of igniting them continues to be researched by other companies. An alternative route was taken by the Austrian company, Voere, which developed a caseless round for the Voere VEC-91 that was electrically fired. This technique makes it possible to greatly increase the ignition temperature of the ammunition, while maintaining the ability to fire it. This would increase the maximum rate and duration a gun could fire at before cooking off rounds, but the VEC-91 never took advantage of this, since it was a bolt-action rifle. As yet, the only weapon that electrically fires caseless ammunition automatically is Metal Storm.
According to various web sites, there was the LMG11 squad-level automatic weapon and the G11 PDW personal defense weapon planned on the same ammunition family as that used by the G11. Some hints of the former caseless PDW design can be seen in the current Heckler & Koch MP7 personal defense weapon. One of the most important reasons as for the creation of the new weapon and the new munition was the issue of weight: the M16A2 with a total of 270 cartridges weighs about 16 lb (7 kg), while a shooter with the G11K2 rifle would be able to carry 600 rounds of ammunition at the same weight. Another design feature of the rifle was the ability to mount three 45-round magazines on rails on the front of the rifle, making reloading much faster. Additionally, a factory-zeroed scope would give the shooter an advantage over an adversary using a rifle with iron sights, though the modern trend is towards integrated scope rails for greater versatility.
 HK ACR
From top to bottom, ACR test rifles from AAI, HK, Steyr, and Colt
HK participated in the U.S. Advanced Combat Rifle Program during the 1980s and 1990s. None of the final four test entrants scored high enough to replace the M16. Some sources report that the low scores resulted from the Army's requirement that the new rifles improve on the M16's score by 100%, and question whether that was a realistic goal.
Reportedly, around 1,000 rifles were delivered to units of the army of West Germany shortly before German reunification in 1990, though the weapon never entered into full production. Reunification imposed new strains on the German army and forced a major reassessment of defense needs. Additionally, the Federal German army inherited the entire East German stockpile of AK-74 assault rifles following the merger. Given the wider political implications of reunification, it was hard to justify the additional cost of the G11.
By 2004, the technology developed for the G11 was licensed for the Lightweight Small Arms Technologies project, the current project of which is a light machine gun prototype for the US Army. The design is intended to be able to proceed with either a cased cartridge using a composite case or a caseless ammunition design developed from the G11. Both ammunition designs are telescoped ammunition like that used by the G11, however the current ammunition design has a plastic case in contrast to the fully caseless G11 ammunition. The design, like the G11, uses a rotating bolt, but rotating along the longitudinal axis of the weapon.