This paper studies practical control design for a novel automatic shell magazine (ASM) with a new fast smooth second-order sliding mode (FSSOSM) control based on disturbance observer.The dynamic model of the ASM with parameter perturbations and nonlinear friction is established.A higher order sliding mode disturbance observer based on super-twisting algorithm is utilized as a robust compensator to estimate the lumped uncertainties.The proposed FSSOSM control is performed to obtain the continuous sliding mode control law and inhibit the chattering phenomenon.The finite time convergence is investigated by utilizing the Lyapunov stability theorem.Three controllers,the traditional sliding mode controller,the proposed FSSOSM controller and a continuous fixed-time second-order sliding mode (CFTSOSM) controller,are compared.Extensive comparative simulation results under three typical working conditions (no-loaded,half-loaded and full-loaded) demonstrate that the proposed control strategy has a high dynamic tracking performance along with a good robustness against model uncertainty.