A firearm frame locking system locks a two-part firearm frame. This is achieved by a firearm frame locking system that includes an upper frame and a lower frame that slide into each other by means of projections that fit into grooves in both the upper frame and the lower frame. In the lower frame, a double-arm lever is located along the longitudinal axis of the firearm. One arm of the double-arm lever extends at least partially into/through a vertical hole in a horizontal rib of the lower frame. A second arm of the double-arm lever ends in the opposite position to a projection in the upper frame. A spring is placed between the horizontal arm and the rib.