In order to improve the firing accuracy of a 12.7 mm heavy machine gun system,the effects of the muzzle mass on the muzzle dynamic responses and firing accuracy were studied with rigid-flexible coupling dynamics,exterior ballistic theory,and corresponding experimental test data.Studies show that: as the muzzle mass increase,the shot dispersion parameters R50,R70 will increase first and then decrease.Since excessive muzzle mass will make it not easy to achieve lightweight design of a machine gun system,it is advisable to reduce the mass nearby muzzle.When reduce the muzzle mass to zero,shot dispersion parameters R50,R7 in the initial design will be significantly reduced from 7.7 cm,11.6 cm to 2.7 cm,5.0 cm,and can be increased by 0.65 and 0.57 times,respectively.