Abstract: A hammer-actuated fastening tool utilizing a powder cartridge for driving a fastener into a workpiece upon discharge of the cartridge includes a retainer clip for maintaining the cartridge in its operative position within the tool for discharge of the cartridge. The tool includes a housing within which a fastener is positionable, a cartridge-holding body supported within the housing defining a bore within which a cartridge is operatively positionable, and an elongated firing pin for transferring the impact of a hammer to the cartridge for discharging the cartridge. A guide member body is positioned about the firing pin for guiding the firing pin relative to the cartridge-holding body from a first position to a second position at which the impact of the hammer is transferred to a cartridge positioned within the cartridge-holding body. The retainer clip is attached to the guide member body so as to be interposed between the firing pin and a cartridge positioned within the bore of the cartridge-holding body.