The Model 57 is a select-fire carbine made by Beretta around the .30 Carbine cartridge. It uses a newly designed magazine much more durable that the American M1/M2 Carbine magazines, and has a tilting bolt locking system coupled with a gas tappet style of piston. Many of the features are distinctly Beretta, like the left side ejection and right side charging handle (like on the Beretta 38 submachine gun family) and the dual triggers (front for semiauto; rear for full auto). Only one contract was made for these carbines, to Morocco in the early 1960s. This is probably because of the ready accessibility of surplus M1 and M2 Carbines for any western-affiliated nation interested in the cartridge.
Many thanks to the Royal Armouries for allowing me to film and disassemble this very scarce automatic rifle! The NFC collection there – perhaps the best military small arms collection in Western Europe – is available by appointment to researchers, and you can browse the various Armouries collections online.