After World War II, as Czechoslovakia came under Communist rule, their army began work on an "intermediate" rifle cartridge for rifle and machine gun use. The Czech government did not standardize ammunition under the Warsaw Pact until the 1960's, so they were free to develop their own munitions and weapons.
The Czech Army had finished out the 1940's with an assortment of German 98K Mausers, Russian Mosin-
In 1958, the Czech Army adopted their Kalashnikov-
Soon the vz-