The pilot was conducting a personal proficiency flight in a rented airplane to practice right-seat operations. During the takeoff roll, after application of full engine power, the right seat slid aft along the seat track to the full rearward position. The pilot was unable to reach the rudder pedals and lost directional control of the airplane. The airplane exited the left side of runway, crossed the grass infield, and impacted a hangar, which resulted in substantial damage to both wings. The pilot stated that he positioned the seat fully forward before takeoff and confirmed engagement of the locking mechanism by rocking the seat. Postaccident examination of the airplane revealed that the seat assembly and seat rails operated as designed, with no mechanical anomalies. It was noted that when the seat was placed full forward against the seat stop, the locking pins could partially align with the forward engagement holes or could contact the seat stop mounting screw. In such cases, the locking pins may feel or appear engaged, thus giving the impression that the seat is locked in place. Examination of the forward seat stop revealed that the mounting screws installed were not the screws specified in the aircraft maintenance manual. However, the installed screw's head shape was similar to that of the specified screw. It could not be determined whether the installed screw affected the function of the seat rail system. The airplane had completed an annual inspection the day before the accident, which included compliance with Airworthiness Directive 2011 10 09 (inspection of the seats and seat rails). The pilot reported no pre-accident mechanical failures or malfunctions that would have precluded normal operation. It’s likely that the right seat locking pins were not fully engaged in the seat track engagement holes at the time of takeoff, which allowed for it to slide aft, resulting in the pilot’s loss of directional control during the takeoff roll.