To improve mechanical actuation systems, this study develops a co-simulation framework to investigate the dynamic response of trigger systems, focusing on firing pin velocity and activation energy. Based on mechanism analysis, a mathematical model relating structural parameters to piercing velocity is derived for clarifying the effects of firing pin mass and spring stiffness on dynamic performance. Combined with LS-DYNA–ADAMS (Automatic Dynamic Analysis of Mechanical Systems) Monte Carlo co-simulation and experimental validation, motion states and manufacturing tolerances on system reliability are evaluated. Tolerance errors produce a firing-pin velocity range of 24.96–32.93 m/s. After parameter optimization, the velocity range shifts to 28.17–33.68 m/s, enhancing stability. Experimental tests raise the average velocity from 27.53 m/s to 31.27 m/s, validating the proposed method and model. This work provides a quantitative basis for tolerance allocation and reliability-oriented design of mechanical actuation systems.