JR Potts, AUS 173d AB (Updated: 10/26/2015):
The RPK was produced to operate with ease and to be nearly jam free. A major bonus was the commonality of parts with the AK service rifle series. The RPK utilizes a simple gas operated system firing from a closed bolt. Pulling the trigger begins the firing action - a round is fired and gas is produced when the powder burns and enters a small gas port pushing small pistons. The bolt is pushed back and the gas pressure is released allowing the bolt to be pushed forward by a spring. For night actions the NSP-2 infrared sight can be attached.
As with all weapons the RPK has her drawbacks. The closed bolt firing action and the barrel are not a quick change in the field. If the operator has good fire discipline few problems occur, however in combat situations discipline can go out the window. Optimal sustained fire is around 80 rounds per minute - if overused, chambered rounds could "cook off" and barrel damage could ensue. The size and weight of the box magazine is limited the amount of ammunition carried by the weapons crew - very different from the amount of belt ammunition carried around the necks of US soldiers in Viet Nam for the M60 general purpose machine gun.
The RPK is still in service, seeing first combat action in the Vietnam War while it is being used by terrorists today in Afghanistan and around the world with many thousands having been produced.