The following information on the “Red 9” 9mm Parabellum Mauser military pistol comes from Chapter 30 of Mauser Rifles and Pistols by W. H. B. Smith. Mauser Rifles and Pistols is also available to purchase in print.
When a Mauser Military Pistol of the general 1898 design is encountered with the figure “9” painted on or burned into the stocks, it indicates a standard Mauser pistol with magazine and barrel adapted to handle the regular 9mm Luger cartridge known in Germany as the “cartridge for Pistole 08.” In other parts of the world it is called “9mm Parabellum” (Latin “for war”). This powerful 9mm cartridge must not be confused with the common 9mm short used in pocket pistols.
During World War I, because of a shortage of Luger pistols and a desire to standardize ammunition insofar as was possible, the Germans utilized Mauser machinery to manufacture these pistols for their regular service ammunition.
Except for such differences as were necessitated by the increase in caliber, this model is identical with the standard 7.63mm type.
The tangent rear sight on this model is graduated only to 500 meters because of the lower muzzle velocity (about 1025 feet per second) of the Parabellum cartridge, as compared with the 7.63mm Mauser (approximately 1375 feet per second). The effective range of the Mauser cartridge when used with a shoulder stock weapon is of course, considerably greater than that of the Luger (or Parabellum) cartridge.
Since the barrel is the standard 7.63mm bored out to 9mm, its walls are not as thick in the larger caliber, though the external diameters are the same.
When these arms are encountered with the stamp of the Prussian Government on the barrel and on the receiver, they indicate weapons made between 1916 and the end of World War I as officers’ service pistols. Arms of this caliber which do not bear the government stamp but do bear standard German proof marks, were assembled from spare parts or manufactured in contravention of the rules of the League of Nations as set up by the Treaty of Versailles after World War I. Large numbers of these arms were exported both to South America and to the Far East. Those found in the United States as a rule will be the official Prussian Government issue, which were brought here as War souvenirs.