Union of Soviet Socialist Republics
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Lateral view of a steel-cased 7.62x39mm FMJ cartridge.

The 7.62x39mm round is a rifle cartridge of Soviet origin that was designed during WWII.  It was first used in the RPD machine gun.  Due to the worldwide proliferation of the SKS and AK-47 pattern rifles, the cartridge is utilized by both militaries and civilians alike.  7.62x39mm ammunition is purportedly tested to function well in temperatures ranging from -50 to 50 degrees Celsius cementing its usefulness in extremely cold polar or hot desert conditions.

The 7.62x39mm cartridge was likely influenced by a variety of foreign developments, especially the pre-war German CeCo 7.75x39mm experimental round, and its developments in the German late-war Intermediate cartridge trials in calibers 7.9mm and 7.62mm.

Shortly after the war, the world's most recognized military pattern rifle was designed for this cartridge: the AK-47.  The cartridge remained the Soviet standard until the 1970s. and is still one of the most common intermediate rifle cartridges used around the world.  It was replaced in Russian service by the 5.45x39mm cartridge.