Today we are looking at a Chinese Type 56 RPD, but we will be focusing on the basic design and why it was adopted in the Soviet Union rather than the details of its use in China. The RPD was the result of research into reduced-power cartridges to replace the 7.62x54R for infantry use. While that round was good for heavy machine guns on mounts, it was found to be excessively powerful for infantry rifle and squad machine guns. The problem is that a more powerful cartridge requires heavier and stronger guns, generates more recoil, and allows fewer cartridges to be carried for any given weight. The Soviet leadership found that the M43 cartridge (7.62x39mm) was sufficiently effective out to 800m, and that covered virtually all squad weapon use in the real world. And so, as the Great Patriotic War came to an end, the Red Army was working on a whole new family of infantry arms in 7.62x39mm.
The rifle adopted was the SKS, the AK served as a submachine gun (originally intended for specialty troops like paratroops and mechanized infantry), and the RPD was the squad support weapon. With its lighter action and cartridge, the standard load out of gun and 300 rounds of ammunition weighed almost half as much as the equivalent load out with the previous DP-27/RP-46 machine gun.
Mechanically, the RPD is a flapper-locked, gas-operated system, very similar to Degtyarev’s prior guns (the DP-27 and DS-39). It is belt-fed, with a drum-like carrier holding a 2-part, 100-round belt. It has a fixed barrel, on the principle that it is to be used for short, controlled bursts and not sustained or continuous fire. In theory, the barrel will overheat at about the same time as the standard 300-round load out is used up, so the added complexity and weight of a changeable barrel is not needed. This compromise was continued in the RPK, which replaced the RPD as a better logistical solution, once the AKM became the standard infantry rifle.