|Caliber||9x19mm Luger / Parabellum|
|Length (stock closed/open)||635 / 813 mm|
|Barrel length||249 mm|
|Rate of fire||500 rounds per minute|
|Magazine capacity||32 rounds|
FBP m/948 submachine gun was developed at Portuguese arms-making factory Fabrica de Braco de Prata, and adopted by Portuguese military in 1948. The FBP m/948 submachine gun was broadly based on two wartime designs – German MP40 (bolt and return spring setup, safety) and US M3 (receiver design, trigger and shoulder stock). FBP m/948 submachine gun was extensively used by Portuguese military and by some former Portuguese colonies.
FBP m/948 submachine gun is a simple blowback weapon that fires from open bolt, in full automatic mode only. The bolt and especially return spring and its external telescoping guide are patterned after the German MP40 submachine gun, although the bolt design is somewhat simplified. The safety, which uses an L-shaped cut in the cocking handle slot in receiver to lock the bolt in the open position is also based on MP40. The overall layout and design of the stamped steel receiver and pistol grip / trigger unit is patterned after American M3 submachine gun. Sliding, telescoping buttstock, made of steel wire, is also copied from US M3 weapon. The FBP m/948 submachine gun was sometimes fitted with optional bayonet lug on the barrel.