Design details

The G3A3 (A4) is a selective-fire automatic weapon that employs a roller-delayed blowback operating system. The two-piece bolt assembly consists of a breech (bolt head) and bolt carrier. The bolt is partially locked in battery by two sliding cylindrical rollers that engage locking recesses in the barrel extension. The breech is unlocked when both rollers are compressed inward against camming surfaces driven by the rearward pressure of the expanding exhaust gases upon the bolt head. As the rollers move inward recoil energy is transferred to the locking piece and bolt carrier which begin to withdraw while the bolt head remains locked. As the bolt carrier clears the rollers, pressure in the bore drops to a safe level, the bolt head is unlocked and begins to recoil backwards at a velocity lower than that of the bolt carrier. The bolt also features an anti-bounce mechanism that prevents the bolt from bouncing off the barrel's breech surface. The spring-powered claw extractor is also contained inside the bolt while the lever ejector is located inside the trigger housing (actuated by the recoiling bolt).[5] The rifle is hammer fired and has a trigger mechanism with a 3-position fire selector switch that is also the manual safety toggle that secures the weapon from accidentally discharging (fire selector in the “E” or “1” position – single fire mode, “F” or “20” – automatic fire, “S” or “0” – weapon is safe, trigger disabled mechanically). The weapon can be fitted with an optional 4-position safety/fire selector group illustrated with pictograms with an ambidextrous selector lever. The additional, fourth selector setting enables a 3-round burst mode of fire.[5] A cut-away of the G3 roller-delayed locking mechanism. The G3A3 (A4) uses either steel (260 g) or aluminum (140 g) double-stacked straight box magazines. The firearm was equipped with iron sights that consist of a rotary rear drum and hooded front post. The rear sight, mechanically adjustable for both windage and elevation, has an open notch used to fire up to 100 m and three apertures used for: 200, 300 and 400 m.[5] The receiver housing has recesses that work with HK clamp adapters used to mount day or night optics. The rifled barrel (contains 4 right-hand grooves with a 305 mm twist rate) is ended with a slotted flash suppressor which can also be used to attach a bayonet or serve as an adapter for launching rifle grenades. The barrel chamber is fluted, which assists in the initial extraction of a spent cartridge casing (since the breech is opened under very high barrel pressure).[5] Standard accessories supplied with the rifle include: a detachable bipod (not included with rifles that have a perforated plastic handguard), sling, cleaning kit and a speed-loading device. Several types of bayonet are available for the G3, but with few exceptions they require an adapter to be inserted into the end of the cocking tube. The most common type features a 6 3/4 inch spear-point blade nearly identical with the M7 bayonet, but with a different grip because of its mounting above the barrel. A variant of this exists with an 9 1/4-inch blade that is completely double-edged like a dagger. A rather shoddily made Pakistani bayonet with a British-style bowie blade also exists, and one of the Eickhorn KCB77 variants fits the G3. The weapon can also mount a 40 mm HK79 under-barrel grenade launcher, blank firing adapter a straight blowback bolt (called a “PT” bolt, lacks the locking rollers) used for firing 7.62x51mm ammunition with plastic bullets, a conversion kit used for training with .22 LR ammunition and a sound suppressor (that uses standard ammunition). Apart from the G3A3 and G3A4 HK also built: the G3A3ZF (essentially a G3A3 with a Hensoldt 4x24 optical sight), the accurized G3SG/1 rifle (hand-selected G3A3’s, equipped with an improved trigger, Zeiss telescopic sight with a variable 1.5-6x magnification and a cheek riser) and the G3K carbine which uses an HK33 handguard and a short barrel (reduced in length to the base of the front sight post), that is too short for use with a bayonet or rifle grenades.[5] The G3 served as a basis for many other weapons, among them: the PSG1 and MSG90 precision rifles, the HK11 and HK21 family of light machine guns, a single-fire version known as the HK91, a sporterized model called the SR9 (designed for the civilian market) and the MC51 carbine, produced by the UK firm FR Ordnance International Ltd. for special forces. The MC51 weighs 3.1 kg (6.8 lb), has a folded overall length of 625 mm (24.6 in), a barrel length of only 230 mm (9.1 in), which produces a muzzle velocity of approx. 690 m/s (2,263.8 ft/s) and a muzzle energy of 2215 J. The MC51 was allegedly manufactured for the British SAS and SBS, who required a compact but powerful weapon, for situations in which the stopping power and armor piercing capabilities of 9x19mm Parabellum round were inadequate. Only 50 weapons were produced, and all were reportedly shipped to the UK special forces. Most of them were soon replaced by the Heckler & Koch HK53 carbine. Another UK-based company called Imperial Defence Services Ltd. absorbed FR Ordnance and continues to market the MC51 standard variant. In addition, a weapon similar to the MC51 called the M41 Offizier is produced by Schwaben Arms GmbH of Germany.[6]