The RPK functions identically to the AK-47. It also uses the same 7.62x39mm ammunition. It has a similar design layout to the AKM and AK-47 series of rifles, with modifications to increase the RPK's effective range and accuracy, enhance its sustained fire capability, and strengthened receiver.
Most notably, the RPK has a heavier and longer barrel than an AKM. This allows the RPK to fire for extended periods of time without major loss in accuracy is due to the barrel heating up. The chrome-lined barrel is permanently fixed to the receiver, and cannot be replaced in the field. It is fitted with a new front sight base, gas block (lacks the bayonet lug) and an under-barrel cleaning rod guide. The barrel also features a folding bipod, mounted near the muzzle, and a front sight base with a lug that limits the bipod's rotation around the axis of barrel. The barrel's muzzle is threaded, enabling the use of muzzle devices such as flash hiders, compensators, and blank-firing adapters. When a muzzle device is not being used, the threads on the muzzle can be covered by a thread protector. The barrel is pinned to the receiver in a modified trunnion, reinforced by ribbing, and is slightly wider than the trunnion used on standard AKM type rifles. Symmetrical bulges on both sides of the front trunnion ensure proper fit inside the receiver.
The RPK's receiver cover is stamped from a smooth 1.5 mm (0.1 in) sheet of steel (compared to the 1 mm sheet metal receiver cover used on standard AKM rifles). Interchangeability of parts between the RPK and AKM is moderate.
The RPK uses a modified AKM recoil spring assembly. It consists of a rear spring guide rod from the AKM, and a new forward flat guide rod and coil spring.
The RPK features a thick laminated wood foregrip, and a fixed laminated wood "club-foot" buttstock, similar to the stock used on the RPD, which is designed to allow the user to fire from the prone position more comfortably. The RPK uses a standard AKM pistol grip.
The weapon can use standard AKM detachable box magazines, but is most commonly used with a 40 round capacity magazine, or a 75 round drum magazine.
The weapon's rear sight leaf is elevation adjustable, and graduated for ranges of 100 to 1,000 meters, in 100 m increments. The rear sight leaf also features a windage adjustment knob, unique to the RPK series of rifles.
Supplied with the RPK are: spare magazines, a cleaning rod, cleaning kit (stored in a hollowed compartment in the butt stock), a sling, oil bottle and magazine pouches (a single-pocket pouch for a drum magazine or a 4-pocket pouch for box magazines). An RPK with a side-folding wooden stock was intended primarily for the air assault infantry. Changes to the design of the RPKS are limited only to the shoulder stock mounting, at the rear of the receiver. It uses a grunion riveted to both receiver walls that has a socket and tang, allowing the stock to hinge on a pivot pin. The grunion has a cut-out on the right side designed to engage the stock catch and lock it in place when folded. The wooden stock is mounted in a pivoting hull, which contains a catch that secures the butt stock in the extended position. The rear sling loop was moved from the left side of the stock body to the right side of the stock frame. Introduced in 1974 together with the AK-74 and chambered for the new 5.45x39mm high-velocity cartridge. The RPK-74 derives from the AK-74 rifle, with modifications that mirror those made to the AKM to create the RPK. The RPK-74 also uses a longer and heavier chrome-plated barrel, which has a new gas block with a gas channel at a 90° angle to the bore axis, and a ring for the cleaning rod. The RPK-74 was also equipped with a folding bipod and a different front sight tower. The muzzle is threaded for a blank-firing device.
The rear stock grunion was strengthened and the magazine well was reinforced with steel inserts.
Additionally, the RPK-74 has a modified return mechanism compared to the AK-74, which uses a new type of metal spring guide rod and recoil spring. The rear sight assembly, forward hand guard and receiver dust cover were all retained from the RPK.
The RPK-74 feeds from a 45-round steel or polymer box magazine, interchangeable with magazines from the AK-74, and is designed to be charged from stripper clips. Drum magazines similar to those used on the previous RPK models were tested during the development phase of the RPK-74, but were discontinued in favor of the 45-round box magazine.
Standard equipment includes: eight magazines, six stripper clips (15 rounds per clip), a speed loader guide, cleaning rod, cleaning kit, sling, oil bottle and two magazine pouches. Some variants do not come with the cleaning kit option.
It is in widespread use by member states of the former Soviet Union, as well as Bulgaria. RPKS-74 The RPKS-74 is the paratrooper model of the RPK-74, equipped with a wooden folding stock from the RPKS. Night variants The RPK family of light machine guns is also available in a night fighting configuration. These weapons are designated RPKN, RPKSN, RPK-74N, and RPKS-74N. They have a side rail mounting on the left side of the receiver that accepts a NSP-3, NSPU, or NSPUM night vision sight.