Shortly after the stamped-receiver AKM rifles went into mass production, Mikhail Kalashnikov and his bureau of technicians and engineers produced what is arguably best general-purpose machine gun in use today. It was adopted into service in 1961 after a surprising upset of a GPMG design by Nikitin. Mechanically, the PK is basically an AK action flipped upside down, to allow for a belt feed on the top of the receiver instead of a box magazine on the bottom.
Like the AK, the PK makes clever and effective use of design elements from several other guns. The mechanism for pulling cartridges out of the belt is taken from the Goryunov SG43, the design of the feed pawl (which is directly powered by the gas piston upon firing) comes from the Czech vz52 LMG, and the barrel quick-change mechanism also comes from the Goryunov. The rotating bolt and gas piston design are form the AK, with the addition of a manually adjustable gas cylinder.
Copying the German doctrine of the universal machine gun, the PK was adopted simultaneously in several different configurations – the regular PK with its integral bipod for infantry use, the PKS mounted on a lightweight tripod for emplacements and better supporting fire, the PKB with spade grips and mountings for armored vehicle use, and the PKT for coaxial tank use, with a remote firing solenoid trigger in place of the stock and pistol grip.
The PK design is an excellent one, and very reliable. It makes very good use of stampings, which the Russians had spent nearly 15 years perfecting for the AK rifle. It is interesting to compare the PK to the US contemporary M60 design, which is a technically quite poor design. On paper the two guns share many common features (long gas piston, stamped receiver, rotating bolt, etc), but the PK was based on a gun completely understood by its designer (the AK), while the M60 was developed from the German MG42 and FG42 by a team that really didn’t understand the subtleties of its parent designs.
In 1969, the design was revised and given the new designation PKM (modernized), along with the PKMS and PKMT. The new version was lightened to 16.5 pounds (down from 19.8), and can be distinguished by a short flash hider, smooth barrel, and ribbed top cover (the original PK has a half fluted barrel, smooth top cover, and long flash hider). Both versions continue to use the antiquated-but-effective 7.62x54R cartridge and metal belts compatible with the Maxim and Goryunov machine guns. The PK and PKM have been adopted and manufactured by many different countries, including pretty much the entire Soviet Bloc.
Sources for Parts
High speed footage of a PKM: