Calibers 7.62×39 mm and 5.56×45 mm are the two famous automatic rifle calibers used worldwide by infantry soldiers. Several years ago, most of European and American countries already changed from 7.62×39 mm to 5.56×45 mm, while other countries still using caliber, 7.62×39 mm and refusing the change. To optimize the advantages of both calibers, a
new automatic rifle caliber 6.8×43 mm emerges. The purpose of this study is to perform a ballistic comparative study of the three mentioned calibers. Interior ballistic calculations were performed using modified Charbonnier semiempirical
model to estimate the weapon interior ballistic parameters. While, the main task of exterior ballistics (i.e., projectile trajectory parameters and energy dissipation during projectile flight at different firing angles) was performed using point-mass two-degree-offreedom trajectory model. It was found that the value of maximum pressure of gases inside the rifles barrel were almost the same, while three different muzzle energies were obtained. They are 2.45 kJ for 6.8×43
mm, 2.1 kJ for 7.62×39 mm, and 1.55 kJ for 5.56×45 mm. The highest energy dissipation along the trajectory was found with 6.8×43 mm projectile. The lowest one was found with 5.56×45 mm projectile all over the range of angles of fire.