Behaviour of 7.62x39mm tracer and API bullets in soft tissue

Some bullets, called tracer and API bullets, contain a pyrotechnical charge. The charge in the bottom of a tracer bullet burns in flight and enables the shooter or an observer to see the bullet's trajectory. An Armor Piercing Incendiary (API) bullet contains a hard core and a pyrotechnical charge that ignites on impact with a hard target. These bullets are designed to both pierce armor and ignite combustible materials. Both tracer and API bullets are quintessentially military ammunition, but some 7.62x39mm caliber variants are occasionally used in crimes. This fact triggered a study on the behavior of these bullets in soft tissue. Two different types of tracer bullets and two different types of API bullets were tested. The tracer bullets behaved similarly in a soft tissue simulant, in terms of energy transfer and deflection. These bullets deflected more from their original trajectory than the tested API bullets and the full metal jacket (FMJ) bullets that were tested as a reference. The two types of API bullets behaved completely different in the soft tissue simulant, especially in terms of energy transfer. One type yawed very late in the simulant and stayed intact, transferring little kinetic energy. The other type yawed early and disintegrated in the simulant, transferring much more of its kinetic energy, causing massive tissue (simulant) disruption. The difference in bullet behaviour was caused by a small but important difference in bullet design with the two types of API bullets.