There is Low poly weapon model for any game (especially in WWII setting).
It is both enough low-poly (just 913 polygon) to be used even for mobile games and well-modeled and detailed even for big serious game. Use cool Normal and Specular maps form this package to achieve amazing result!
Comparable sub machine guns was widely used during WWII. Most of them are copy of the German SMGs; Weapon as this primarily used by the British Royal Navy during the Second World War, and to a lesser extent by Royal Air Force regiments