We were wondering what drove the U.S. Ordiance Dept. in 1940, to adopt the 30 M1 Carbine round rather than the more powerful 357 Magnum. Seems the 9 mm Parabellum with double stack magazine even would have been a better choice for the intended purpose. There was no other weapon chambered for the 30 Carbine, and few have been since WWII. Was it because the 357 Mag was a rimmed cartridge and difficult to make a reliable magazine for?