An Introduction to Exterior Ballistics and the Forensic Application

Ballistics is the science of projectiles and firearms, and the study of the effects of being fired on a bullet, cartridge, or gun. Exterior ballistics also known as external ballistics is the part of ballistics that deals with the behavior of a non-powered projectile while in flight. The flight of projectiles (in this case bullets) must obey certain laws of physics. Scientists and engineers have developed the necessary mathematics to both describe and predict the flight of projectiles through the atmosphere.
Ballistics is the science of projectiles and firearms, and the study of the effects of being fired on a bullet, cartridge, or gun. Exterior ballistics also known as external ballistics is the part of ballistics that deals with the behavior of a non-powered projectile while in flight. The flight of projectiles (in this case bullets) must obey certain laws of physics. Scientists and engineers have developed the necessary mathematics to both describe and predict the flight of projectiles through the atmosphere.

Exterior ballistics lies between transitional ballistics (the study of a projectile's behavior from the time it leaves the muzzle until the pressure behind the projectile is equalized) and terminal ballistics (the study of how a projectile behaves when it hits its target and transfers its kinetic energy to the target).

Modern bullets, even from handguns, can travel a mile or more if launched at a relatively high departure angle. Bullets from centerfire rifles are capable of several miles of flight before impacting the ground or an object. There are a number of forces acting on a projectile in flight that will never be accurately known and there are typically greater uncertainties associated with an actual incident. For example a private investigator or forensic scientist in the field will never know the actual muzzle velocity associated with a long-distance shot. The details of the environmental conditions (ie precise location and exact weather) at a shooting scene are also likely unknown.

Private investigators and forensic scientists must be aware of these uncertainties during the scene of an investigation’s reconstructive efforts. Fortunately, contemporary ballistics programs and modern computers allow for the analysis and manipulation of variables so all possible scenarios can be observed and analyzed.

At a scene of investigation involving ballistics the only certainty is a bullet has arrived at some known location after traveling some distance. In order to determine the location of origin, exterior ballistic calculations are used. A subsequent search of the determined location or origin may lead to the recovery of pertinent physical evidence or witnesses.

Some constants are measurable with the aid of modern instrumentation. For example one of the primary measurable constants is gravitational attraction. Gravitational attraction and its effect on the bullet is constant and predictable. A fired bullet, regardless of its muzzle velocity, will be acted on immediately after it leaves the muzzle and will ultimately fall to the ground. The necessary observation of gravitational attraction can be seen in the following application. In order to strike an intended target from a particular distance, the gun must be sufficiently elevated above the shooter’s line of sight.

The study and observation of exterior ballistics is a fascinating subject matter. Private investigators and forensic scientist must be aware of the laws of physics and the numerous seemingly unknown variables that tell the story of the bullet’s flight from the muzzle and final resting position.
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