What cartridge, also known as 9 mm Luger by the C.I.P. or 9 mm NATO by NATO, is used in the submachine gun the MP 40?
9×19mm Parabellum The 9×19mm Parabellum, also known as 9 mm Luger by the C.I.P. or 9 mm NATO by NATO (abbreviated 9mm, 9mmP, 9×19mm or 9×19) is a cartridge that was designed by Georg Luger and introduced in 1902 by the German weapons manufacturer Deutsche Waffen und Munitionsfabriken (DWM) (German Weapons and Munitions Factory) for their Luger semi-automatic pistol.
6.5×55mm The 6.5×55mm (designated as the 6.5×55 Swedish by the SAAMI and 6,5 × 55 SE by the C.I.P.) is a first-generation smokeless powder rimless bottlenecked rifle cartridge. Other, less common names are 6.5×55mm Swedish Mauser, 6.5×55mm Mauser and 6.5×55mm Krag. It was developed in 1891 for use in the new service rifles then under consideration by the United Kingdoms of Sweden and Norway. The two nations had independent armies and consequently the normal procedure at the time was for their respective governments to use the same ammunition and then purchase small arms of their choice. Norway adopted the Krag–Jørgensen rifle, while Sweden adopted a Mauser rifle design.