HK53

Heckler & Koch HK33
The HK33A2 with a Trijicon ACOG optical sight.
Type	Assault rifle
Place of origin	West Germany
Service history
In service	1968–present
Used by	See Users
Wars	Vietnam war Communist insurgency in Malaysia Turkey-PKK conflict
Production history
Manufacturer	Heckler & Koch, MAS (licensed), MKEK(licensed)
Produced	1968—2001
Variants	See Variants
Specifications
Weight	HK33A2: 3.65 kg (8.05 lb) HK33A3: 3.98 kg (8.8 lb) HK33KA3: 3.89 kg (8.6 lb) HK53: 3.05 kg (6.7 lb)
Length	HK33A2: 920 mm (36.2 in) HK33A3: 940 mm (37.0 in) stock extended / 735 mm (28.9 in) stock collapsed HK33KA3: 865 mm (34.1 in) stock extended / 675 mm (26.6 in) stock collapsed HK53: 755 mm (29.7 in) stock extended / 563 mm (22.2 in) stock collapsed
Barrel length	HK33A2: 390 mm (15.4 in) HK33KA3: 332 mm (13.1 in) HK53: 211 mm (8.3 in)
Cartridge	5.56×45mm NATO
Caliber	5.56mm
Action	Roller-delayed blowback
Rate of fire	HK33A2: 750 rounds/min HK53: 700 rounds/min
Muzzle velocity	HK33A2: 950 m/s (3,117 ft/s) HK33KA3: 880 m/s (2,887.1 ft/s) HK53: 750 m/s (2,460.6 ft/s)
Effective firing range	100–400 m (328–1,312 ft) sight adjustments
Feed system	25-, 30-, or 40-round detachable box magazine
Sights	Rotary rear aperture drum, hooded foresight

The HK33 is a 5.56mm assault rifle developed in the 1960s by West German armament manufacturer Heckler & Koch GmbH (H&K), primarily for export.

Capitalizing on the success of their G3 design, the company developed a family of small arms (all using the G3 operating principle and basic design concept) consisting of four types of firearms: the first type, chambered in 7.62×51mm NATO, the second—using the Soviet 7.62×39mm M43 round, third—the intermediate 5.56×45mm caliber and the fourth type—chambered for the 9×19mm Parabellum pistol cartridge.

The HK33 series of rifles were adopted by the Brazilian Air Force (Força Aérea Brasileira or FAB), the armed forces of Thailand and Malaysia where they were produced under a license agreement. The rifle was also license-built in France by MAS and in Turkey by MKEK.

The HK33 is a selective fire weapon with Heckler & Koch's roller-delayed blowback system of operation. It employs a two-piece bolt consisting of a bolt head with a pair of rollers and bolt carrier. Upon firing, the two cylindrical rollers in the bolt head are cammed inward by inclined surfaces of the barrel extension and impart a rearward motion on the locking piece, which also propels the bolt carrier rearward. This built-in mechanical disadvantage delays the movement of the bolt head relative to the bolt carrier which is withdrawing at four times the velocity of the bolt. The rollers soon compress entirely into the bolt head, clearing the locking recesses of the barrel extension, and both parts now continue rearward together, opening the breech and actuating the extraction and feeding cycles. The chamber is opened under very high pressure, thus the chamber received a series of flutes in order to increase extraction reliability and prevent sticking of the spent casing to the chamber walls.