The PK (ПК, Пулемёт Калашникова, Pulemyot Kalashnikova, Kalashnikov's machine gun in English) is a Russian machine gun.
In 1955, the Main Artillery Directorate of the Soviet Union published requirements for a 7.62mm caliber general purpose machine gun to be adopted. In 1958, a machine gun jointly designed by Grigory Nikitin and Yuri Sokolov passed field tests, and based on the above field tests, it was decided that the Nikitin-Sokolov design would be put into production in 1960 and be manufactured by the Kovrov Mechanical Plant. When the Nikitin-Sokolov weapon was nearing completion, a group of designers from the Izhevsk Mechanical Plant, namely Mikhail Kalashnikov and a slew of other designers, submitted their prototype to the Main Artillery Directorate, based on the well-proven AK-pattern action. Both the Nikitin-Sokolov and Kalashnikov designs participated in various trials, with the final verdict being that the Kalashnikov design was more reliable and cheaper than the Nikitin-Sokolov design, and as such, was put into production. When put into service, the PK replaced the SGM and RPD machine guns in military service. The PK was later modernized in 1969 to become the PKM machine gun.
The PK machine gun is based on the well-proved action of the AK rifles, and is a development of the RPD machine gun and AKM assault rifle. The receiver is made of stamped steel, and has double walls made of steel plates for additional rigidity. The PK has a quick-detachable barrel, locked into place with a barrel lock which is partially fluted to aid in heat dissipation. The weapon's bore is chrome-lined and has a 1:9.45 inch twist rate. The weapon's muzzle is threaded, which allows for other peripherals such as flash hiders and suppressors to be attached. The weapon's furniture is made of birch plywood laminates. The bolt and carrier design of the weapon is remarkably similar to those of AK-pattern rifles, as is the cleaning and stripping procedure of the PK; however, when compared to an AK, the PK's bolt and carrier are mounted upside down, with the piston and gas system located underneath the barrel. Another thing unlike the AK is that the PK is of an open bolt design; this aids in the cooling of the weapon to prevent cook-off. This is due to the airflow allowed into the chamber in between firing shots, which aids in cooling the weapon down. The weapon's breech is locked by a rotating bolt, with two locking lugs aiding the process by engaging locking recesses located in the receiver. The gas piston is hinged to the bolt carrier assembly of the weapon; the piston's vertical travel makes it possible to bend the whole assembly and make cleaning and maintenance much easier. The rear of the bolt features spiral-shaped cuts which allow for controlled rotation of the bolt. The mainspring is located in the bolt carrier assembly's main channel, and the weapon's extractor is mounted in the rear part of said assembly. The charging handle for the weapon is mounted on the right, as with most Russian machine guns, and does not reciprocate when the weapon fires.
- PKS (ПКС, Пулемёт Калашникова Станковый, Pulemyot Kalashnikova Stankovyy, Kalashnikov's mounted machine gun in English)
Mounted variant of the PK.
Modernized version of the PK adopted in 1969.
- PKT (ПКТ, Пулемёт Калашникова Танковый, Pulemyot Kalashnikova Tankovyy, Kalashnikov's tank machine gun in English)
Tank-mounted version of the PK developed in 1968.
- Zastava M84
Yugoslav clone of the PK, with the only difference being that the stock is not hollowed out.
- Zastava M86
Yugoslav clone of the PKT.