An apparatus for mortars for simulating the loading and firing of live ammunition by using a dummy shell. The apparatus includes a mortar, a spacer piece, and a dummy shell. The spacer piece and dummy shell are inserted into the mortar barrel. The length of the spacer piece and dummy shell are such that the top of the dummy shell projects a distance past the muzzle of the barrel. The spacer piece includes a firing pin mechanism including a firing pin and a triggering mechanism. A triggering pin projects from a top plate of the spacer piece and is movable from a projected position into a retracted position for triggering. The firing pin mechanism includes spring biassed rods which project out from the top plate of the spacer piece and are urged inwards by the dummy shell. The firing pin mechanism is biassed by a latch which is releaseable by an electromagnet.