Abstract: The powder actuated tool has a modular construction which comprises: a firing pin module; a pistol grip module; and a fastener driving module. The firing pin module and the fastener driving module are readily detachable from the pistol grip module so that if any module is damaged, or needs maintenance, it may be readily removed and replaced at low cost and at no inconvenience to the user. The fastener driving module includes a barrel which is reciprocally slidably mounted in the pistol grip module. A fastener driving piston is carded in the barrel and a piston return pawl is mounted on the pistol grip module for returning the piston from a fired position to a firing position via a slot in the barrel. Combustion gas ports in the barrel bleed gases from the barrel bore adjacent to the firing chamber. The bled gases pass through external grooves in the barrel to reentry ports communicating with the barrel bore, whereby tool noise is muffled.