Abstract: A powder actuated tool for driving a fastener into a concrete steel or other hard surface. The tool has a main housing in which a barrel assembly is held. The barrel assembly is permitted to move in and out a short distance and is spring loaded in the out position. A cartridge is held at the inner end of the barrel. A piston is held within the barrel and has an upper end near the cartridge and a lower end adjacent a fastener to be driven. When the cartridge is detonated the piston is driven against the head of the fastener driving it into the concrete or other substrate. A firing pin is held in a breech block and is moved downwardly by contact with a firing hammer. The firing hammer is also held by the breech block and is spring loaded to move downwardly. Its downward movement is restrained by the contact of a tab resting on a ledge of the breech block.