KAPOW / May 2014 7
External Ballistics
External ballistics is the part of the science of ballistics that deals with the behavior of non-powered projectiles in flight. External ballistics is frequently associated with firearms, and deals with the unpowered free-flight phase of the bullet after it exits the barrel and before it hits the target, so it lies between transitional ballistics and terminal ballistics. When in flight, the main forces acting on the projectile are gravity, drag, and, if present, wind. Gravity imparts a downward acceleration on the projectile, causing it to drop from the line of sight. Drag, or air resistance, decelerates the projectile with a force proportional to the square of the velocity. Wind makes the projectile deviate from its trajectory. During flight, gravity, drag, and wind have a major impact on the path of a projectile, and must be accounted for when predicting how the projectile will travel.
Terminal Ballistics
Terminal ballistics is the study of behavior and effects of a projectile when it hits its target. Terminal ballistics is relevant for small caliber projectiles, as well as for large caliber projectiles. An early result is due to Newton, the impact depth of any projectile will reach before stopping in a medium. In Newtonian mechanics, a projectile stops when it has transferred its momentum to an equal mass of the medium. If the impactor and medium have similar density, this happens at an impact depth equal to the length of the impactor. There are three basic classes of bullets: those designed for maximum accuracy at varying ranges, those designed to maximize damage to a target by penetrating as deeply as possible, and those designed to avoid over-penetration of a target by deforming to control the depth to which the bullet penetrates, which as by-product, deals more damage inside the wound, third class may limit penetration by expanding or fragmenting.
Caroline Zylstra