On the human-rifle system, the human body is affected by the firing impact. The firing impact will reduce the firing accuracy and change the initial shooting posture. Therefore the study of biomechanical characteristics using human-rifle modeling and numerical investigation is needed. The muscle-skeleton model was developed by the finite element method using beam and spar elements. In this study, a structural analysis has been performed in order to investigate the human body impact by firing a 5.56mm small caliber machine gun. The firing experiments with a standing shooting posture were performed to verify analytical results. The result of this study shows analytical displacements of the human-rifle system and experimental displacements of real firing. In the results, the analytical displacement on the human body is presented.