Russian tactics called for a reduced weight firearm capable of accurate and sustained fire. As a result the Russian RPK series was developed. The Russian RPK series was developed in the late 1950's, and feature a longer, heavier barrel to aid in long range accuracy. The Russian RPK utilized a stregthened AKM type sheet metal receiver. Advantages of this system are many of the parts between the RPK and AKM are interchangeable.
Additional advantages are the ability to use the same magazine used by the issued assault rifle.
One point to note is the design of the stock. The non shooting hand is used to grab underneath the stock, pulling it tighter to the shooter's shoulder. This allows greater control and accuracy. Results of this weapon are mixed. Caliber is 5.56mm Nato.