The PK machine gun was developed by Mikhail Kalashnikov’s engineering team right about the time they were putting the finishing touches on the AKM. The PK is in many ways an AK rifle action enlarged, flipped upside-down, and mated with a belt feed mechanism. It uses the same belt design as the previous Soviet 7.62x54R machine guns (the Maxim, SG43, and RP46).
The PK was improved in a few relatively minor ways to become the PKM, and the Yugoslav military put it into production in 1984. The weapon is rugged, reliable, relatively lightweight, and arguably the best universal machine gun design ever produced.
Thanks to Marstar for letting me examine and shoot their M84!