Abstract: An automatic device with interchangeable interface for the introduction of cartridges in the bifilar or monofilar magazines of automatic and semi-automatic arms, comprising a plate (1) with a cartridge-guide ledge (2), placed above a vertical track (3) for transferring said cartridges into a suitable seat (18) from which a piston (13) introduces the same, one by one, into an arm magazine by means for a movable pin (10) provided in such a way that it may bend at right angle.