The clearances in pitch mechanism of gun have an important influence on firing concentration. The present study designs a set-up of experimental research on pitch mechanism of gun with clearances and carries out corresponding numerical simulations and experiments. The clearance in slider-guide joint, a typical clearance in pitch mechanism of gun, is considered in the set-up. Sinusoidal excitation is used to get dynamical response signals of gun; results of the experiments show that the response signals in time domain reflect clearance size. In the same intensity under sinusoidal excitation, the peak value of gun barrel’s time-domain signal is larger with the clearance enlargement. The current work can be referred as a basis for dynamical clearance adjustment and the gun design.