A detent is the key mechanism for rail launchers, which constraints heading movement of the missile and releases the missile safely during launching. The values of lock and unlock force directly determine the flight safety of a hanging missile on aircraft. In this paper, the keys which influences unstable unlock force value were found out through analyzing working principle of the detent. The unlock force value distribution can be reduced effectively through using appropriate lubrication to reduce the friction coefficient of the contact surface or using the zero arm of friction. This paper provides the methods for production and can be used as measurement of the detent. At the same time, the reasoning methods for improving and modifying the detent were provided.