The behaviour of three standard small calibre projectiles in soap blocks

A study of three standard small calibre projectiles fired from the ranges of 30 and 100 m against soft soap blocks was performed. The assault rifles used in the tests were the Finnish M 62, the Russian AKM 47 and the American M 16 A 1 with standard ammunition. Impact velocity was measured with photocells and exist velocity with foils. The respective kinetic energies and the rate of transferred energy were calculated. The soap block was cut into two pieces after the shot. The diameter of the cavity was measured at every 10 mm along the trajectory, the volume of cavitation was calculated and the blocks were weighed before and after the shot. The bullets were collected when technically possible. At the range of 30 m the 7.62 M 62 bullet was already very stable. The two other projectiles especially the 5.56 calibre were fasttumbling and their volume of cavitation in soap blocks was about 1.75 times more than that of the 7.62 M 62 projectile. At the range of 100 m the stability of the two 7.62 projectiles is almost equal, but the 7.62 AKM 47 projectile released much more of its impact energy to the target. Furthermore, the 5.56 calibre projectile is unstable and goes on showing early tumbling and total break-up behaviour. The ratio between the volumes of cavitation was 1:2:3 (M 62:AKM 47:M 16 A 1).