STK-54

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Siinrak Tionsal Kinel 1954
STK-55AB with K55 No. 5 (upper), and K55 No. 4 (lower) bayonets.
TypeAssault Rifle
Place of originMirhaime Federation
Service history
In service1954-present (removed from frontline service in 1994)
Production history
DesignerKilian Mainne Domman nar Giker'ha
Designed1983
ManufacturerReingiker Ardamezou (Reingiker Armory)
Produced1954-1987
Specifications
Weight4.0kg (8.8 lbs)
Length1016mm (40 in)
Barrel length508mm (20 in)

Cartridge6.5x42mm M42
Feed system24-round detachable box magazine
Sightsdrum aperture rear sight (adjustable from 200 to 600 m/yd in 100 m/yd increments)

The STK-54 (From Fefsen: Siinrak Tionsal, Kinel 1954, 'Assault Rifle, Type 1954') is a Mirhaimian assault rifle developed by Mirhaimian small arms designer Kilian Mainne Domman nar Giker'ha, and manufactured by Reingiker Ardamezou (Reingiker Armory). It was the standard issued rifle of the Mirhaime Realm Defence Forces from 1954 to 1995 with variants and derivatives still serving within other Mirhaimian uniformed services till this day.

The STK-54 was designed in 1952 by Reingiker Armory at the request of the Mirhaimian Realm Guards to replace the semi-automatic TK-38. The weapon was heavily influenced by contemporary designs, in particular its long stroke piston gas system. Several prototypes were made, and the rifle passed trials in late 1953; proceeding to full manufacturing by 1954. From 1954 to 1987, approximately 1,820,000 rifles (of all variants) were manufactured, and put into service with the Mirhaimian Realm Defence Forces.

In 1955, a derivative of the rifle, the STK-54SA passed Sarvian military and was put into service with the Worker's Armed Forces under the designation of Rk-55A. Approximately 300,000 Rk-55As were manufactured under license by Defense Interprise "Kommunardi" for use by the Sarvian military.

The rifle also saw success within the Mirhaimian civilian sector under the commercial name of M55. According to the Bureau of Firearms, Swords, and Explosive Control (BFSEC), approximately 2,132,000 M55-platform weapons were registered, and in circulation as of 2022; 442,000 of which are fully automatic.

History

ETK-244 Prototype chambered in 6.5x42mm.

The first prototype of the STK-54, the ETK-213, chambered in the standard 6.5x42mm M42 cartridge, was designed in 1949 as a response to the growing number of designs capable of fully automatic firing by Mirhaimian small arms designer Kilian Mainne Domman nar Giker'ha, the designer of the semi automatic TK-38 in service with the Mirhaimian Realm Defence Forces. Domman stated that the Volkian AR series, notably its distinctive gas-operated mechanisms, had a significant influence on the STK-54's design.

The prototype failed to capture the interest of Mirhaimian military commanders at the time, who saw the deployment of such a design to replace the relatively new semiautomatic rifle design in service as unnecessary waste. However, given the apparent efficacy of similar weapons in service with other forces, Domman's prototypes were once again considered in competition with a variety of other designs. With minimal funding from the Guards Infantry Ordnance Board, Domman continued work on the rifle with a small team of engineers towards 1952 when the ETK-244 prototype was presented to the GIOB for testing and field trials.

At the Empress Freida Ke'sed Testing Grounds, the ETK-244 prototype was tested in a competitive service rifle competition conducted by the GIOB. Tests were conducted from the end of the 1952 to the early 1953, and eventually led to the ETK-244 prototype being adopted as the STK-54 with heavy modifications to external components.

By 1993, all STK-54 models were superseded by the STK-92 platform chambered in the newer 6.5x39mm cartridge. The weapon is still kept in service by some rear-line services, including the Artillery and Armored Corps, until around 2007.

The STK-54 (7.62x51mm) was manufactured under license by Defense Interprise "Kommunardi" for use by the Sarvian military.

Design details

Operating mechanism

The STK-54 series of rifles are selective fire weapons operated by a gas-driven piston system similar to the one seen on the Volkian AR system. It uses ignited powder gases channeled through a vent in the barrel to drive a long stroke piston located above the barrel in a gas cylinder to provide power to the operating system. When fired, a portion of the propellant gases are evacuated into the gas cylinder through a 1.9 mm (0.08 in) port, drilled at a 30° angle in the barrel, and a channel in the gas block. The high-pressure gases drive the piston rod (which is attached to the bolt carrier) rearward. During this rearward movement, a cam slot machined into the bolt carrier engages a cam pin on the bolt and rotates the bolt, unlocking the action. The arrangement of parts on the bolt carrier assembly provides for a degree of free travel, allowing gas pressure in the barrel to drop to a safe level before unlocking. The weapon features a self-regulating gas system and a rotary bolt breech locking mechanism (equipped with two locking lugs), which is rotated by a helical camming groove machined into the bolt carrier that engages a control pin on the bolt. To the immediate rear of the chrome-plated piston head is a notched ring which provides a reduced bearing surface and alleviates excess gas build-up. As the bolt carrier travels back, it compresses the return spring guided in a hollowed section of the bolt carrier and the return energy contained in the spring drives the moving assembly back forward, stripping a new round from the box magazine and locking the action. The cocking handle is attached to the bolt carrier on the right side of the receiver and reciprocates with each shot; the handle is bent upwards allowing for operation with the left hand while the shooting hand remains on the pistol grip.

Barrel

Early production model (Series A1. 1954-1955) were outfitted with barrels which had a rifling twist of four grooves, right-hand twist, one turn in 14 inches (1:355.6 mm or 64 calibers) bore - the same as one used on the semi automatic TK-38. After finding out that under unfavorable conditions, the reduced powder charge bullets the STK-54 was tuned to could yaw in flight at long ranges, the rifling was soon altered. Starting from series A2, STK-54s had an improved rifling with six grooves, right-hand twist, one turn in 12 inches (1:304.8 mm or 54.8 calibers) for increased accuracy and was optimized to adequately stabilize the K431 ball and K442 tracer bullets. Further improvements were made starting from Series A4 (1964-1969), as newer barrels were optimized for firing the heavier NK312 ball and long D410 tracer bullets and have six grooves, right-hand twist, one turn in 7 in (1:177.8 mm or 32 calibers).

Feeding

The standard magazine capacity is 25 rounds. There are also 10, 20, 30, and 40-round box magazines, as well as 75-round drum magazines.

All magazines, including the 75-round drum magazines, were of heavy steel construction - this combined with "feed-lips" (the surfaces at the top of the magazine that control the angle at which the cartridge enters the chamber) machined from a single steel billet makes STK-54's magazines highly resistant to damage. This, however, made the standard magazines heavy but was not seen as a disadvantage due to their reliability.

Early STK-54 magazines had light sheet-metal bodies with prominent reinforcing ribs which weighed around 0.33 kg (0.73 lb) empty. A second generation steel-reinforced dark-gray 25-round 6.5x42mm magazine with a matte nonreflective surface finish was introduced starting from Series B1 (1974-1982), fabricated from steel-reinforced ABS plastic. Later production magazines were noticably black in color due to a change in surface finish. The second generation magazine weigh approximately 0.25 kg (0.55 lb) empty. This rapid transition from steel to mainly plastic magazines yields a significant weight reduction and allows a soldier to carry more ammunition for the same weight.

Sights

All variants of the STK-54 are equipped with an drum aperture sight adjustable from 100m to 600m increments. The front post is fully adjustable for both windage and elevation zero and is enclosed in a protective hood. Low-light flip-up front blade and rear sight elements have three self-luminous tritium capsules (betalights) which are calibrated for 100 m when deployed.
Standard-issued K55 No. 5 Bayonet, and ZK-55 Bipods.

Accessories

A number of standard-issued accessories for the STK-54.

A number of accessories were provided with the STK-54 in the Mirhaimian Realm Defence Forces as standard issued. These include a blank firing device, a standard model M55 No. 5 Bayonet, a web magazine carrier, as well as a foldable bipod which is attached to the bayonet sheath when in transport. The bayonets are installed by slipping the 17.7 mm (0.70 in) diameter muzzle ring around the muzzle and latching the handle down on the bayonet lug under the front sight base. All variants of the STK-54 has a foldable carrying handle built into the upper receiver of the rifle.

The STK-54 in Mirhaimian service was never adapted to use underbarreled grenade launcher as the transition from conventional rifle grenades to UBGLs did not occur until the advent of the lighter STK-92 assault rifles which superseded the STK-54 in standard service within the Mirhaimian Realm Defence Forces.