An instrument for applying one or more surgical fasteners includes a tubular shaft having a distal end through which each fastener is deployed. A delivery system is contained within the tubular shaft for advancing the surgical fasteners along, and out of, the instrument. An actuator is operatively associated with the delivery system. One or more wall structure modifications in the tubular shaft, such as openings, reliefs or cut-outs, interact with the delivery system. An outer tubular shaft is mounted over the wall structure modifications to reinforce the instrument against permanent deformation or inward distortion if excessive forces are encountered.