The 7.63×25mm Mauser (.30 Mauser Automatic) round was the original ammunition of the Mauser C96 service pistol. This cartridge headspaces on the shoulder of the case. The basis of this cartridge was the 7.65mm Borchardt of 1893, the only successful automatic pistol cartridge in production at the time. The 7.63mm Mauser is sometimes confused with the later 7.65mm Parabellum (.30 Parabellum), also a bottlenecked pistol cartridge.
Firearms chambered for the 7.63mm Mauser cartridge include the C96 and variants and copies, the Astra Model 900 and variants, the 1911-pattern Star models A and M, and a handful of pre-World War II submachine guns such as the Swiss Bergmann M/20 exported to China and Japan and the SIG MKMO.
The 7.63mm Mauser cartridge was the basis for the 7.62mm Tokarev, adopted by the Soviet Union. Although the case dimensions of the two cartridges are nearly identical, the 7.62mm Tokarev has a stronger powder charge and is generally not suited for use in Mauser C96 pistols or other firearms chambered for 7.63mm Mauser. However, the 7.63mm Mauser could be used in firearms chambered for the 7.62mm Tokarev: something that became important later during WWII on the Eastern Front when the Germans began using captured 7.62x25mm weapons, notably the PPSh-41 and fed them with 7.63mm Mauser rounds. During the Finnish-Soviet Winter War and World War II, the cartridge was issued by Finnish and German forces for use in captured Soviet submachine guns, due to its inherent substitutability for the Soviet 7.62×25mm round. According to Finnish military archives, the Finnish Army ordered one million rounds of 7.63mm Mauser from FN for this purpose.
7.63mm Mauser ammunition is still manufactured by Fiocchi, Sellier & Bellot, and Prvi Partizan. Reloadable Boxer-primed cartridge cases can be formed from 9mm Winchester Magnum by simply resizing and trimming. Alternately, they can be formed from 5.56mm NATO but this requires an additional step of inside neck-reaming. RCBS makes a forming die set that includes the reamer. These cases will bulge slightly on firing, and proper Mauser stripper clips will need to be carefully squeezed in a vise in order to secure an adequate grip on the smaller rims. For the Mauser, the use of .311" or .312" bullets produce the best accuracy - the Hornady 85 grain .311" XTP being a particularly good choice, but Tokarev TT-33 and Czech CZ-52 pistols have tighter barrels and chambers and function better with .308" bullets of the sort intended for the 7.65mm Luger and .30 M-1 Carbine rounds.