Abstract: A dispensing gun (2) for us with a cartridge (1), comprising a frame (14) supporting a piston rod (10) and one or more operating levers (16,102) connected to the frame (14) and acting on the piston rod (10), characterised by a reversible ratchet mechanism (26) carried on the piston rod (10) and operated on by one to more operating levers (16,102) for reciprocal motion of the piston rod (10) and a piston (11) for use with a cartridge (1), wherein the piston (11) is attachable to a piston rod (10) in a cartridge (1), the piston comprising a hollow rigid member and a flexible member (12), the flexible member (12) having a periphery which maintains a movable seal with the inside wall of the cartridge, a space being formed between the rigid member and the flexible member allowing movement of the flexible member into the space.