The urban environment provides many surfaces from which bullets or shotgun pellets may ricochet, and factors determining whether ricochet will occur include nature of the target surface, angle of incidence, shape of the projectile, and projectile velocity.
Research on the ricochet of bullets and shotgun pellets indicates that surfaces have a critical angle of incidence below which projectiles will ricochet. Bullet shape and makeup determine whether the bullet will ricochet in a given situation. Low velocity projectiles are more likely to ricochet than high velocity projectiles, and angles of ricochet are typically low. The angle of ricochet increases with increasing angle of incidence; the angle of ricochet is generally lower than the angle of incidence. Although attempts have been made to produce a mathematical model of bullet ricochet, the bullet's trajectory after ricochet is generally impossible to predict in any detail. Bullets may tumble after ricochet due to the change in orientation of a spinning projectile's axis produced by collision with a surface. When shotgun pellets ricochet from a surface, the pellets will spread out parallel to the surface. Bullets and shotgun pellets lose energy when they strike a surface, but they retain enough energy after ricochet to inflict serious or even fatal injuries. When police officers investigate shooting incidents in which ricochet has occurred, they should pay special attention to the nature of wounds suffered by shooting victims, bullet or shotgun pellet deformation, presence of trace evidence, ricochet marks on surfaces, and ricochet geometry. 27 references and 4 figures