The Model 1918/30 is a semiauto-only carbine made by Beretta in between the early Model 1918 submachine guns and the excellent Model 38 family. It was marketed (well, sold) primarily to security and police forces, for whom the semiautomatic limitation was not a particular hindrance. It is chambered for the 9mm Glisenti cartridge, which is dimensionally identical to 9x19 Parabellum but more lightly loaded.
Mechanically the carbine is a simple blowback design, and very light and handy. It has a rather short barrel (12.5 inches), but has been exempted from the NFA regulations on short-barreled rifles. Magazines were made in 12- and 25-round capacities (the one seen here is a 25-rounder).