5.56 mm enhanced penetration cartridge The 5.56mm RS101 enhanced penetration cartridge is used against exposed personnel protected by body armor, single and group targets and other equipment at ranges up to 600 m. The cartridge is used in the AK-101, AK-102 assault rifles, RPK-201 machine gun, M16A2 assault rifle and other 5.56mm NATO firearms under various climatic conditions at temperatures from - 50 to + 50 °C.