OBJECTIVE: This study investigated the effects of mass and vertical center-of-mass position of combat items attached to a tactical vest, as well as marksmanship posture on rifle marksmanship performance, postural sway, and perceived workload during a simulated rifle shooting task. BACKGROUND: A tactical vest serves as a load carriage system in addition to providing body protection. Its design, particularly the mass and vertical position of attached combat items, may impact postural control during rifle shooting and thus marksmanship performance. METHOD: Thirty-two participants performed a simulated rifle shooting task on a force plate with a tactical vest on. Three independent variables were considered: load mass (4 levels), vertical load center-of-mass position (4 levels), and marksmanship posture (2 levels). The dependent variables were: 6 rifle marksmanship performance measures, 7 postural sway measures, and a perceived workload measure. RESULTS: Heavier load mass significantly degraded rifle marksmanship performance, and increased postural sway and perceived workload. Marksmanship posture significantly affected rifle marksmanship performance and postural sway. The kneeling posture resulted in less postural sway and better marksmanship performance than the standing posture. Vertical load center-of-mass position affected only part of the marksmanship performance measures and did not affect the measures of postural sway and perceived workload. CONCLUSION: Reducing combat item mass on tactical vests and enhancing soldier postural control ability would improve rifle marksmanship and soldier lethality. APPLICATION: The study findings inform the development of future military tactical vests and rifle marksmanship training, highlighting the need for lightweight gear design and postural control training.