External Ballistics and Accuracy of Lead Free Bullets in 5.56x45mm NATO

Several nations have moved to lead free bullets in 5.56x45mm NATO for use as duty ammunition by military personnel. This study reports on the external ballistics and accuracy of two lead free bullet designs that have been fielded to date, the 62 grain lead free hard core bullet manufactured by RUAG and the 62 grain lead free bullet manufactured by ATK at the Lake City Arsenal. Doppler RADAR was used to determine aerodynamic drag curves for each bullet from Mach 1.5 to Mach 3.0 when fired from rifles with twist rates of 1 in 7”, 1 in 8”, and 1 in 9”. Drag coefficients were consistent with claims by the manufacturers when fired from 1 in 7” and 1 in 8” twist barrels; however, drag coefficients varied up to 50% higher when fired from the 1 in 9” twist barrel, suggesting marginal stability. The 1 in 9” twist affects the drag of the ATK bullet more than the RUAG bullet. Accuracy of the RUAG bullet was less than 2 minutes of angle (MOA) when fired from a match grade rifle and less than 4 MOA when fired from a service grade rifle. However, accuracy of the ATK bullet was worse (2 MOA to 4 MOA) from the 1 in 7” twist match grade rifle and poor (6 MOA to 8 MOA) from a service grade rifle with 1 in 9” twist. The original Miller formula for gyroscopic stability of each bullet shows good agreement with experimental data. This formula may be used to estimate gyroscopic stability within 5% for a variety of twist rates, muzzle velocities, and atmospheric conditions.