Riley Defense RAK74-C-SF Semi-Automatic Rifle 5.45x39mm 16.25" Chrome-Lined Barrel (1)-30Rd Magazine Adjustable Front & Rear Sights Teak Wood Upper And Lower Hand Guards Side-Folding Triangular Metal Stock Black Finish

The 5.45X39mm (5.45X39 Russian, Soviet, Kalashnikov) was introduced by the Soviet Army in 1974 along with the AK-74 as a replacement for the AK-47 and its 7.62X39mm cartridge. Mikhail Kalashnikov designed the rifle, essentially an update of his more famous AK-47, but did not design the cartridge. Although case length is the same 39mm, the 5.45X39 is not based on the7.62X39mm case; with a smaller base diameter and a .220-inch bullet it is much more similar to the 5.56x45mm NATO cartridge, but with a shorter and slightly fatter case. The 5.45X39mm uses a 54-grain bullet at 2950 fps, so is slightly less powerful than the NATO cartridge, but is loaded to higher pressure (55,000 psi versus 52,000). The Russian Army has since replaced the AK-74, but retained the 5.45X39mm cartridge. Its standard bullet is a three-part design with copper jacket, lead core, and a steel penetrating rod; case material is typically steel. — Craig Boddington