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?
MP 40 The MP 40 ("Maschinenpistole 40") was a submachine gun chambered for the 9×19mm Parabellum cartridge. It was developed in Nazi Germany and used extensively by the Axis powers during the Second World War.
7×64mm The 7×64mm (also unofficially known as the 7×64mm Brenneke, though its designer's name officially never was added as a part of this cartridge name) is a rimless bottlenecked centerfire cartridge developed for hunting. As is customary in European cartridges the 7 denotes the 7 mm bullet caliber and the 64 denotes the 64 mm case length. The 7×64mm is a popular hunting cartridge in Central Europe and can, due to its 11.95 mm case head diameter and 84 mm overall length, easily be chambered in Mauser 98 bolt action rifles that were then standard issue in the German military.