PK machine gun
The PK, is a belt-fed general-purpose machine gun, chambered for the 7.62×54mmR rimmed cartridge. The modernised variant is known as the PKM, which features several enhancements over the original PK design including a more ergonomic design.
Designed in the Soviet Union and currently in production in Russia, the original PK machine gun was introduced in 1961 and the improved PKM variant was introduced in 1969. The PKM was designed to replace the SGM and RP-46 machine guns that were previously in Soviet service.
The PK remains in use as a front-line infantry and vehicle-mounted machine gun with Russia's armed forces and has also been exported extensively and produced in several other countries under license.
History
The Main Artillery Directorate of the Soviet Union adopted specification requirements for a new 7.62 mm general-purpose company and battalion-level machine gun that was to be chambered for a rifle cartridge in 1955.In 1958 a machine gun prototype the Nikitin-Sokolov PN1, developed by G.I. Nikitin and Yuri M. Sokolov, successfully passed field tests. Based on the results of the tests it was decided in 1960 to manufacture a batch of Nikitin-Sokolov machine guns for service tests and then put the machine gun into production at the Kovrov Mechanical Plant. However, the PK had flaws, the main flaw being that the machine gun did not resist water and snow very well. Water and snow had a tendency to enter the gas piston. If, after firing, the machine gun was in the water, then after two or three shots the machine gun could fire exclusively only shot by shot. After a single shot, the shooter had to reload the machine gun and move the slide manually two or three times. The army therefore asked Nikitin to solve this problem, but the engineer took too long to resolve this problem. In order to force Nikitin to work faster, the Main Artillery and Missile Directorate decided in 1958 to restart the competition. For that a team of Izhevsk Mechanical Plant designers, headed by M.T. Kalashnikov, and further consisting of V.V. Krupin, V.N. Pushchin, A.D. Kryakushin, as well as Startsev, Kamzolov, Koryakovtsev, Yuferev, joined the competition. Kalashnikov and his team accepted the task while at the same time, they were already working on the design of the AKM and the RPK. Kalashnikov accepted the task despite his workload and the fact that Nikitin's PN1 had already been chosen by the army and that the latter was supported by certain ministries and senior officers. Their machine gun prototype was based on the well-proven gas-operated rotary-bolt design of the Kalashnikov-pattern arms.
The Kalashnikov and the Nikitin-Sokolov prototypes underwent service tests in the Central Asian, Odessa, and Baltic Military Districts, as well as at the Vystrel officer training courses in late 1960. The Main Missiles and Artillery Directorate and the Ministry of the Defence Industry preferred the Kalashnikov design. The PK could resist water perfectly, but it was also much easier to maintain and manufacture, because it reused the same ammunition bands as the Maxim or SG-43, while the PN1 used a new type of bands which was not yet in production at the time. Furthermore, according to Kalashnikov, its competitors attempted to bias the test by asking operators to lower the rate of fire because of overlapping bands during long bursts. There was also another incident during the test, according to Kalashnikov, the recoil of the PN1 was poorly distributed and a large part ended up in the stock; the pressure was so great that one of the soldiers responsible for testing the PN1 broke his cheekbone.
Based on the test results, the army preferred the Kalashnikov design. In 1961, the 7.62x54R mm Kalashnikov universal machine gun was adopted and put into production. The production of the PK/PKS took place at the Kovrov Mechanical Plant and used the tripod mount and an ammunition belt boxes originally designed for the Nikitin-Sokolov prototype machine gun.
Nikitin's and Sokolov's machine gun design was later used in the 12.7 mm NSV heavy machine gun that was put into production in 1971.
In June 2024, it is reported that the PKZ will eventually replace the PKM in Russian military service.
Production
The PKM and other variants are in production in Russia and are currently exported to many other nations. Additionally, various models are manufactured locally around the globe. A remotely controlled PKT version reportedly entered service in November 2023. Zastava Arms produces the PK under license as the M84, and it remains in use with many of the former Yugoslav successor states. The most recent modification is the Russian PKP Pecheneg, which features a forced air cooling barrel and longer barrel life up to 10,000 rounds.Design details
The original PK was a development of Kalashnikov's AKM assault rifle and the accompanying RPK light machine gun design that featured stamped receivers. The PK uses the 7.62×54mmR Eastern Bloc standard cartridge that produces significantly more bolt thrust when compared to the Eastern Bloc 7.62×39mm and 5.45×39mm intermediate cartridges.With the use of a single spare parts kit and two barrel assemblies the service life of the modernised PKM machine gun series is guaranteed for at least 25,000 rounds.
Operating mechanism
The bolt and carrier design are similar to the AK-47 and other modernised Kalashnikov-pattern designs, as is the stripping procedure performed to remove those mechanisms from the gun for cleaning. The bolt and bolt carrier are however oriented upside down compared to the AKM, with the piston and gas system being underneath the barrel.Unlike the AKM and RPK the PK machine gun series is an open bolt design, which improves heat management during automatic fire compared to closed bolt designs and helps avoiding the dangerous phenomenon known as "cook-off", wherein the firing chamber becomes so hot that the propellant contained in a chambered round unintentionally ignites, making the machine gun fire until the ammunition is exhausted. Open bolt designs typically operate much cooler than closed bolt designs due to the airflow allowed into the chamber, action and barrel during pauses between bursts, making them more suitable for constant fully automatic fire. General-purpose machine guns like the PK are further normally issued with several quick change barrels that during prolonged intense use are swapped out allowing one barrel to cool while the machine gun fires with the other.
The rimmed 7.62×54mmR cartridges are set in a metal ammunition belt and are held against the shoulder inside non disintegrating looped links, leaving the rim exposed at the rear. The belt is mounted from the right side into the feed way of the PK machine gun. The machine gun uses a non-reciprocating charging handle on the right side of the receiver to charge the gun. Since the PK uses a rimmed rifle cartridge and closed-link belts used for feeding, a two-stage feed mechanism with a preliminary extraction of a cartridge from a belt link was preferred over a direct ammunition feed design often used for rimless cartridges.
The PK machine gun is equipped with a lever-type feed mechanism introduced in Louis Stange's MG 39 Rh and copied in the Czechoslovak machine guns like vz. 52 and vz. 59, which is operated by the feed lever. The lever, which is simplified compared to the prior art, is mounted on the right wall of the receiver and wraps around the bolt carrier with its feed pawl and roller. The rest of the mechanism is mounted either on the receiver cover or on the ammunition feed tray cover hinged under it. The PK feed mechanism pulls the rimmed 7.62×54mmR cartridges out from the back of the ammunition belt and drops the cartridges down into the feed way, allowing the bolt to strip and feed the cartridges into the chamber for firing.
The PK feed mechanism is radically different from that of 7.62×51mm NATO machine guns based on the MG 42 feed mechanism that typically incorporate a much larger articulated feed cam, lever, and pawl assembly that pushes rimless cartridges out forward from their links directly into the chamber for firing.
The PK fires from the rear sear. The breech is locked by a rotating bolt, with two locking lugs engaging locking recesses in the receiver. The gas piston is hinged to the bolt carrier assembly, and its vertical travel makes it possible to bend the group making machine gun assembly and disassembly for maintenance easier. The protruding rear part of the bolt carrier assembly features spiral shaped cuts, which provide a controlled rotation of the bolt. The mainspring is accommodated in the bolt carrier assembly slide channel. A cartridge extractor with a latch is mounted in the rear part of the bolt carrier assembly. The cocking lever, mounted on the right, is not integral with the bolt carrier and does not reciprocate as the gun fires.
The gas cylinder is mounted under the barrel and fitted with a gas regulator with three fixed positions. The gas regulator opens corresponding holes to change the amount of expanding propellant gases bled off out of the gas cylinder into the atmosphere, thus varying the amount of energy transferred on to the long-stroke piston.