Firearm a battle rifle such as the Karabiner 98k, but the chief differences defining an assault rifle are select-fire capability and the use of a rifle round of lesser power, known as an intermediate cartridge. Soviet engineer Mikhail Kalashnikov quickly adapted the German concept, using a less-powerful 7.62×39mm cartridge derived from the standard 7.62×54mmR Russian battle rifle round, to produce the AK-47, which has become the world's most widely used assault rifle. Soon after World War II, the Automatic Kalashnikov AK-47 assault rifle began to be fielded by the Soviet Union and its allies in the Eastern Bloc, as well as
Assault rifle in 5.56×45mm. During the 1990s, Russia developed the AK-101 in 5.56×45mm NATO for the world export market. In addition, Bulgaria, Czechoslovakia, Hungary, Poland and Yugoslavia (i.e., Serbia) have also rechambered their locally produced assault rifles to 5.56mm NATO. "The AK-74 assault rifle was a Soviet answer to the US M16." The Soviet military realized that the M16 had better range and accuracy over the AKM, and that its lighter cartridge allows soldiers to carry more ammunition. Therefore, in 1967, the USSR issued an official requirement to replace the AKM and the 7.62×39mm cartridge. They soon began to develop the AK-74