Heckler & Koch HK33


The HK33 is a 5.56mm assault rifle developed in the 1960s by West German armament manufacturer Heckler & Koch GmbH, primarily for export.
Building on the success of their G3 design, the company developed a family of small arms 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; the third, chambered in the intermediate.223 Remington and 5.56×45mm NATO; and the fourth type, chambered for the 9×19mm Parabellum pistol cartridge. Commercially the HK33 was a successful design but it did not sell as well as the G3.
The HK33 series of rifles were adopted by the Brazilian Air Force, the armed forces of Thailand and Malaysia where they were produced under a licence agreement. The rifle was also licence-built in Turkey by MKEK, and exported from France branded as MAS but actually made in Germany.

Design details

Operating mechanism

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 head carrier which is withdrawing at significant higher velocity of the bolt head. 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 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.
The G3 roller-delayed blowback mechanism designed around 7.62×51mm NATO ammunition was downsized and revised for reliably using 5.56×45mm NATO ammunition. This required changing geometrical transmission ratio relationships between parts.
Based on the geometric relationship arising from the angles of the roller contact surfaces of the locking piece and the barrel extension recesses, the recoil of the bolt head is delayed by a ratio of 3:1 for the 5.56×45mm NATO chambering. Thus during the same period of time, the bolt head carrier moves 3 times faster than the bolt head. This ratio is continued until the locking rollers have been withdrawn from the barrel extension recesses.
Like the G3 bolt the HK33 bolt features an anti-bounce mechanism that prevents the bolt from bouncing off the barrel's breech surface. The "bolt head locking lever" is a spring-loaded claw mounted on the bolt carrier that grabs the bolt head as the bolt carrier group goes into battery. The lever essentially ratchets into place with friction, providing enough resistance to being re-opened that the bolt carrier does not rebound. The spring-powered claw extractor is also contained inside the bolt while the lever ejector is located inside the trigger housing.
Further like the G3 the G33 also contains a spring extractor and a buffer. The ejector lever was installed in the trigger housing and is actuated by the recoiling bolt.

Features

The HK33 is a modular weapon system. Its butt-stock, fore-stock and pistol-grip/fire-control assembly may be changed at will in a variety of configurations. Simple push-pins hold the components in place and removing them will allow the user to remove and replace parts rapidly.
The rifle is disassembled into the following components for maintenance: the receiver/barrel, stock with return spring, bolt assembly and trigger pack in pistol grip.

Trigger

The HK33 has a conventional hammer-type firing mechanism. In the standard version, the rifle comes equipped with an ambidextrous trigger group with a selector lever that is simultaneously the weapon's safety. The "safe" setting mechanically disables the trigger. The trigger groups can be swapped out to meet the user's specific mission requirements. H&K offers several different trigger assemblies: a three-shot burst fire control group with selector lever/safety ; a "Navy" trigger unit and a four-position trigger group.

Feeding

The rifle is fed from 20- or 25-round steel magazines weighing 250 g or 40-round aluminum magazines. 30-round arch magazines were also introduced for use with the rifle. Turkish MKEK-made rifles are issued with 30-round polymer magazines.

Barrel

The barrel contains 6 right-hand grooves and terminates with a slotted flash suppressor that enables the use of rifle grenades and supports a standard G3-type bayonet that mounts above the barrel. The barrel chamber is fluted, which assists in the initial extraction of a spent cartridge casing.
Initially the rifle was produced with a 305 mm twist rate barrel, which was later upgraded to the faster 178 mm twist rate.

Sights

The firearm is equipped with a relatively low iron sight line that consists of a Drehvisier a rotary rear drum and hooded front post. The rear sight is mechanically adjustable for both windage and elevation with the help of tools. This deliberately prevents non-armorers to zero the iron sight line. The rotary drum features an open V-notch for rapid target acquisition, close range, low light and impaired visibility use and three apertures used for: in increments for more precise aiming. The 1 V-notch and 2 or aperture settings have an identical point of aim. The V-notch and apertures are calibrated for 5.56×45mm NATO ball ammunition.
The receiver housing has recesses that work with STANAG claw mounts/HK clamp adapters used to mount day or night aiming optics.
The Hensoldt Fero 4×24 telescopic sight and mount assembly were developed for designated marksman use. The Fero elevation knob features Bullet Drop Compensation settings for in increments calibrated for 5.56×45mm NATO ball ammunition.

Accessories

Included with the rifle are a detachable bipod, bayonet, sling, cleaning kit and a magazine loader. Additionally, the HK33 can be used to mount a 40 mm under-barrel HK79 grenade launcher or a blank-firing adaptor.
During its production life the rifle received several minor improvements. The fixed stock was strengthened and the synthetic forearm replaced with a handguard that allows a lightweight bipod to be attached and stowed into two grooves at the base. The shoulder pad in rifles fitted with a telescopic stock was changed to a concave type used thus far in the MP5 series.

Variants

;HK33A2
;HK33SG/1
;HK33A3
;HK33KA3
;HK53KL
;HK13
;Harrington & Richardson T223
;Type 11
;MA-11
;MA-12

Sporting variants

;HK43
;C-93

Combat history

A copy of the Heckler & Koch HK33 was built under licence by Harrington & Richardson as T223 during the Vietnam War. Although heavier than the M16, it was used in small numbers by SEAL teams due to its available 40-round magazine. In Myanmar, the Karen National Liberation Army fielded government-made HK33s. Thai government units fielded HK33s during the South Thailand insurgency. Some of these rifles were seized by groups such as the Patani United Liberation Organisation or the Gerakan Mujahidin Islam Patani. The Kurdistan Workers' Party often claimed it seized HK33s from the Turkish forces.

Users