Break-up behaviour of some small calibre projectiles when penetrating a dense medium

A study of the break-up patterns of two types of standard ball small calibre bullets fired from a range of 100 meters against targets made of soft soap was performed. A flash X-ray set-up was used to study the behaviour of the bullets while penetrating the soap. A simplified calculation of the stresses affecting the bullets was performed. It turns out that one predominant factor in the break-up process is the tumbling of the projectile. The longitudinal rotation velocity of the bullets is often so great that this is sufficient to cause-centrifugal stresses of high enough magnitude to cause rupture of the bullet lead core. This in combination with the high retardation forces acting on a bullet penetrating a dense medium at large angles of yaw is sufficient to cause an almost inevitable break-up for fast-tumbling bullets.