The 7.63×25mm Mauser round was the original ammunition of the Mauser C96

Mauser C96

The Mauser C96 is a semi-automatic pistol that was originally produced by German arms manufacturer Mauser from 1896 to 1937...

 service pistol. This cartridge headspaces on the shoulder of the case. The basis of this cartridge was the 7.65×25mm Borchardt cartridge of 1893, the only successful automatic pistol cartridge in production at the time. The 7.63 mm Mauser is sometimes confused with the later 7.65×21mm Parabellum

7.65×21mm Parabellum

The 7.65×21mm Parabellum is a pistol cartridge that was introduced in 1898 by German arms manufacturer Deutsche Waffen und Munitions Fabriken for their new Pistol Parabellum...

 (.30 Luger), also a bottlenecked pistol cartridge.

The 7.63 mm Mauser cartridge was the basis for the 7.62×25mm Tokarev round adopted by the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

.