RPK 7.62-mm & RPK-74 5.45-mm Light Machine Guns .

The RPK is a variant of the AKM assault rifle. It has a longer, heavier barrel; a stamped metal bipod; and a heavier type of fixed, wooden buttstock. The modified receiver of the RPK can accommodate its larger-diameter barrel. The RPK normally feeds ammunition from either a 40-round curved box magazine or a 75-round spring-loaded drum magazine. However, it can also use the 30-round curved box magazine of the AKM, if necessary. It has a chrome-plated barrel, chamber, and gas piston. It also has a cyclic rate reducer built into the trigger mechanism. The users usually install luminous night sights on the front and rear sights. Some RPKs can mount an infrared night-sighting device. The RPKS is a folding-stock version used by airborne troops. The RPK has a maximum effective range of 800 meters in either automatic or semiautomatic mode. Almost all of the moving parts of the RPK are interchangeable with those of the AK or AKM assault rifles.  

Just as the RPK is the squad machine gun version of the AKM, the RPK-74 is a machine gun version of the AK-74, firing the same ammunition. The RPKS-74 is a folding-stock version of the weapon. Instead of the prominent muzzle brake used on the AK-74, the machine gun has a short flash suppressor. The magazine is longer than that normally used with the AK-74, but the magazines are interchangeable. The RPK-74 has a bipod. The 5.45-mm round of the RPK-74 has a considerably higher muzzle velocity than the 7.62-mm round of the RPK. However, both weapons probably have the same maximum range (2,500 meters) and effective range (800 meters). Unlike the RPK, the RPK-74 is compatible with the front firing ports of the BMP.  

AKSU-74 5.45-mm Submachine Gun .

The AKSU-74 is a modified version of the AK-74 assault rifle with a much shorter barrel (207 millimeters versus 413 millimeters) and a conical flash suppressor instead of a muzzle brake. Like the AKS-74, it has a folding metal stock. The overall length of the submachine gun is only 492 millimeters with stock folded or 728 millimeters with extended stock. The rear sight is a flip-type U-notch. The front sight is a cylindrical post. The Soviets designed the AKSU-74 as a weapon short enough to be handled easily when the crew enters and exits vehicles. The device at the end of the barrel functions as an expansion chamber to bleed off gases that would otherwise cause a violent recoil. With a loaded weight of 3.106 kilograms, the submachine gun is considerably lighter than the assault rifle AK-74 and has a somewhat higher rate of fire