The eccentric mass of projectile has great influence on the stability of in-bore motion.In order to explore its specific mechanism,two typical states of static unbalance and couple unbalance are simulated.The variation laws of projectile lateral overload,nutation angle and axis distance with projectile trip are obtained.The results show that when the projectile is in static unbalance or couple unbalances state,the lateral overload,nutation angle and the axis distance of the projectile increase significantly,especially in the muzzle section.The lateral overload and nutation angle can well reflect the unstable swing of the projectile in the bore,and can be used to characterize the stability of the projectile in the bore.