Abstract: The injector assembly receives fasteners such as bolts used in the manufacture of composite aircraft wing structures, at a high speed from a supply thereof, such as a cartridge. The injector assembly includes a post assembly which includes a hollow post housing having a post mass and a mass stop pin positioned within the housing. The bolt moves through a feed tube assembly, a muzzle member and into a chamber portion of the injector assembly. A urethane contact member is positioned at a forward end of the mass. A source of compressed air moves the mass and the contact member into a position slightly past the rear end of the housing and into a chamber portion of the injector assembly. When the bolt contacts the contact member at high speed, the mass is moved back toward a base portion of the post assembly. The mass is sufficient to dissipate the kinetic energy of the moving bolt without damage thereto.