A reaction mass for a launching tube having a centrally positioned propellant charge for propelling a missile at its forward end and a reaction mass located rearwardly of the propellant charge which is propelled at the rear end, comprises an inert, readily fragmentizing, expellable reaction mass comprising a glass material which is internally prestressed and which disintegrates at the launch. The reaction mass is advantageously in the form of a glass cylinder which is either connected to a metallic pusher member arranged rearwardly of the propellant charge which is pushed by the ignition of the charge in a rearward direction, or it may comprise a glass cylinder which includes its own pusher head formation. The pusher itself is arrested by a brake positioned at the rear exit. In addition, the rear exit is closed by a diaphragm which may shatter after ignition of the propellant charge. The reaction mass may also comprise a front pusher face which is engaged with a rear brake positioned at the rear opening or it may comprise a plurality of layers of glass held to a pusher head which is arrested at the rear opening. In still another embodiment, the glass may comprise a plurality of flat discs held together in an assembly to a pusher member.