5.45x39mm is an experimental Soviet intermediate cartridge, developed after analysis of captured American 5.56x45mm munitions during the Vietnam War. Much like the Americans, the Soviets realised that a low-calibre, high-velocity cartridge offers a number of advantages, such as improved accuracy, range, and a reduction in both recoil and weight. Concurrently, the new Izhevsk A-3 Assault Rifle would be developed, which would later be known as the AK-74.
Because it is an intermediate cartridge with a spitzer-type bullet, it typically does 2d6 DMG | 2 PEN.