DSA RPD Featureless Belt Fed Rifle 7.62x39mm. Available in California from Cordelia Gun Exchange!
Shortly after World War II the AK-47 was designed, which later became the world’s most widespread military-pattern rifle. The cartridge remained the Soviet standard until the 1970s. It was largely replaced in Russian service by the 5.45×39mm cartridge, which is used by the current-issue AK-74M service rifle and its variants. In the 21st century the 7.62×39mm remains a common service rifle chambering, including for newly developed rifles.
7.62×39 -Wikipedia