Ballistics (Forensic Science)
A ballistic body is any object used to exert force to make another object move or change in form, state, or direction. A bullet, for example, is a ballistic body when it is propelled by the sudden increase of pressure that takes place within a handgun or other firearm when the trigger is pulled and a discharge of explosive powder propels the bullet forward in a direction dictated by the barrel of the weapon. When the bullet exits the weapon, it is subject to the laws of ballistics. As the projectile reaches its target, its velocity and trajectory cause distinctive entry and exit wounds.
The science of firearms ballistics is divided into four components: internal ballistics, transition ballistics, external ballistics, and terminal ballistics. Internal ballistics is the study of the forces that cause the acceleration of ballistic bodies; in the case of a bullet fired from a gun, internal ballistics is concerned with the detonation of the bullet, its discharge from the chamber, and its pathway through the barrel. Transition, or intermediate, ballistics is the study of the immediate effects on ballistic bodies as they leave the barrels of weapons; this area of ballistics focuses on forces such as air pressure, gravity, and air density, which act collectively on projectiles as their initial acceleratory force is reduced.
External ballistics is the study of projectiles’ flight through the air. This includes the examination of changes in...
(The entire section is 297 words.)
Criminal Cases (Forensic Science)
Because the barrels of firearms are rifled (that is, they have raised and lowered spiral surfaces) to impart spin to bullets, distinctive marks (striations) are left on bullets as they swirl down the shafts of barrels after firing. The first recorded use of such marks as evidence in a criminal case took place in 1835. It was found that bullets fired from a weapon taken from the home of the primary suspect had a distinctive ridge that was identical to the ridge seen on a bullet recovered from the scene of the crime. When confronted with this evidence during questioning, the suspect confessed to the crime. Nearly seventy years later, in 1902, attorney Oliver Wendell Holmes, Jr., introduced ballistics evidence in a court of law. In a murder case, Holmes had a local gunsmith test fire a weapon belonging to the suspect into a wad of cotton stuffing. Under magnification, the marks on the test-fired bullet were seen to match those on the bullet retrieved from the crime scene, and this evidence was presented to the jury.
Shortly thereafter, two ballistics experts of that time, Calvin Goddard and Charles Waite, began compiling a database of information on all known gun manufacturers and on specific types of handguns as well as the marks made on bullets fired from them. Waite later invented the comparison microscope, which forensic scientists use to make side-by-side comparisons of the marks on two bullets at a time.
(The entire section is 338 words.)
Forensic Techniques (Forensic Science)
Experts in forensic ballistics perform many different kinds of analyses, including making bullet comparisons, matching projectiles to weapons, and estimating the lengths of projectile flights, which enables them to determine the types of weapons used and the locations of the operators of weapons when they were fired. During investigations of crime scenes involving shootings, ballistics experts analyze the impacts of bullets on victims, whether wounded or dead, to determine the types and sizes of projectiles fired and the types of weapons used, the distances from the shooters to the victims, and the angles at which the shots were fired.
If bullets, cartridges, or cartridge cases are not found at the scene of a fatal shooting, a forensic pathologist will usually analyze the victim’s wounds to determine information about the type of weapon used. Entry wounds are generally smaller than exit wounds and have dark rings around the injured surfaces, and by examining these, experts can often determine the width and thus the likely caliber of the bullets that made the wounds. This technique is referred to as wound ballistics.
When bullets are recovered from crime scenes, ballistics experts compare the striations on the bullets to those on other bullets from known sources. If the firearm suspected to have been used in a given crime is available, a test bullet is shot from that weapon and then the marks on that bullet are...
(The entire section is 587 words.)
Further Reading (Forensic Science)
Carlucci, Donald E., and Sidney S. Jacobson. Ballistics: Theory and Design of Guns and Ammunition. Boca Raton, Fla.: CRC Press, 2008. Comprehensive work covers all aspects of the topic, including the theory and fundamental physics of ballistics, design techniques for firearms and ammunition, and the tools used to investigate firearms-related crimes.
Heard, Brian J. Handbook of Firearms and Ballistics: Examining and Interpreting Forensic Evidence. New York: John Wiley & Sons, 1997. Thorough volume focuses on the science of forensic firearms analysis.
Rinker, Robert A. Understanding Firearm Ballistics: Basic to Advanced Ballistics, Simplified, Illustrated, and Explained. 6th ed. Clarksville, Ind.: Mulberry House, 2005. Provides an easy-to-understand general introduction to theory of weapons ballistics.
Zukas, Jonas A., and William P. Walters, eds. Explosive Effects and Applications. New York: Springer, 1998. Collection of essays by experts focuses on the component of ballistics concerned with the explosive impacts of bullets.
(The entire section is 142 words.)
Ballistic Weapons (Magill’s Guide to Military History)
A ballistic weapon is a projectile weapon. That is, all ballistic weapons involve hurling or throwing an object over a distance. The word ballistic comes from the Greek word, ballein, meaning “to throw.” A bow and arrow, an automatic pistol, and an intercontinental ballistic missile (ICBM) are all examples of ballistic weapons.
Early Ballistic Weapons
The first ballistic weapon was created the first time a person picked up a rock and threw it. Many thousands of years elapsed, however, between that first thrown rock and the emergence of formal ballistic weapons systems or the recognition of the science principles that could explain and improve their performance. Prehistoric hunters and warriors used trial and error to invent projectile weapons that allowed them to kill game or their enemies from a distance. Innovations such as slings meant rocks could be hurled with far more force than a rock from someone’s unassisted hand. Using a sling, a hunter could easily kill small animals, such as rabbits and squirrels.
A sling could also be a potent defensive weapon and, in the hands of a skilled user, was potentially deadly in battle. The best-known example of a sling being used in combat may be the biblical story of David and Goliath, but slings are mentioned in Greek and Roman histories of warfare as well as being shown in paintings on pottery and building walls as part of the standard equipment carried by a...
(The entire section is 1605 words.)
Ballistics (Encyclopedia of Science)
Ballistics is the study of projectile motion. A projectile is an object that has been launched, shot, hurled, thrown, or projected by any other means and that then travels on its own along a ballistic path. For instance, a baseball player throwing a ball from center field to the infield usually throws the ball in a slightly upward direction. The ball's path travels along an arc from the outfield to the infield. Mathematically, the arclike path taken by the ball is known as a parabola.
Ballistics has long been a subject of interest to scientists because bullets, cannon shells, arrows, and other weapons travel in ballistic paths. Military leaders have always valued the information that scientists were able to provide them concerning the proper way in which to aim their guns and bows in combat.
Projectile motion without air resistance
Consider a bullet fired from a rifle that is held parallel to (in the same direction as but never touching) the ground. The path taken by that bullet is affected by two forces. The first force is the velocity given to the bullet by the force of the rifle. (Velocity is the rate at which an object moves in a specified direction; it is measured in meters per second.) That force tends to make the bullet move in a straight line, out of the mouth of the rifle and parallel to the ground. If there were no air present, there...
(The entire section is 622 words.)
Ballistics (World of Forensic Science)
When a forensic investigation involves a shooting, ballistics becomes an important facet of the investigation. Ballistics is a term that refers to the science of the flight path of a bullet. The flight path includes the movement of the bullet down the barrel of the firearm following detonation and its path through both the air and the target.
Tracing the path of a bullet is important in a forensic examination. It can reveal from what direction the bullet was fired, which can be vital in corroborating the course of events in the crime or accident.
It is an obvious truism that the distance that a bullet can travel depends on its speed. A higher speed imparts more energy to the bullet. The frictional resistance of the air and the downward pull of gravity will take longer to slow the bullet's flight, as compared to a bullet moving at a lower initial velocity.
Generally, a bullet fired from a rifle will carry more energy than a bullet fired from a handgun. This is because the stronger firing chamber of a rifle is able to withstand the increased explosive power of a larger quantity of powder that would likely rupture the barrel of the handgun. Detonation of the powder in a rifle or handgun supplies the thrust to propel the bullet down the barrel.
Expansion of the exploding gunpowder generates pressure, which is measured as the force of the explosion that pushes on the area of the bullet's base. This area is essentially the diameter of the barrel of the firearm, which remains constant. Thus, the explosive energy that passes to the bullet depends on the mass of the bullet multiplied by the force of the explosion multiplied by the time that the force is applied (i.e., the time the bullet is in the barrel). A longer barrel will produce a faster moving bullet.
Once a bullet leaves the rifle or gun barrel, the aforementioned frictional and gravitational forces begin to slow its speed, producing a downward arc of flight. The frictional force is affected by the bullet's shape. A blunt shape will present more surface area to the air than will a very pointed bullet.
Another factor that affects the flight of a bullet is called yaw. As in an orbiting spacecraft or a football tossed through the air, yaw causes a bullet to turn sideways or tumble in flight. This behavior is decreased when the object spins as it moves forward (the spiraling motion of a football). The barrel of a rifle or gun contains grooves that cause the bullet to spin. More damage results from a bullet that is tumbling rather than moving in a tight spiral.
The shape of a typical bulletuch like a football with one end blunt instead of tapereds a compromise that reduces air resistance while still retaining the explosive energy that allows the bullet to damage the target.
The composition of a bullet is also important. Lead is commonly used to form the core of bullets. However, because it tends to deform, the blending in of other metals (typically antimony and copper) produces a bullet that can withstand the pressure of flight and impart high energy to the target upon impact.
Copper is often used to jacket the inner lead core of a bullet. However, some bullets are deliberately made without this full metal jacket. Instead, the bullet has a tip made of lead or a tip that is hollow or very blunt. These bullets deform and break apart on impact, producing more damage to the target than is produced by a single piece of metal. This is because the bullet's energy is dissipated within a very short distance in the tissue.
Forensic and medical examiners are able to assess the nature of tissue damage in a victim and gain an understanding of the nature of the bullet used.
A bullet produces tissue damage in three ways. First, a bullet can shred (lacerate) or crush tissue or bone. Bullets moving at relatively low velocity do most of their damage this way. Fragmentation of bone can cause further damage, as the bone shards themselves become missiles.
The second form of damage is known as cavitation. This damage is produced by the forward movement of air or tissue in the wake of the bullet. The wound that is produced by the bullet is destructively broadened by the force of the moving air or tissue. In a tissue, this produces even more structural damage.
Third, the air at the front and sides of a very fast moving bullet can become compressed. The explosive relaxation of the compression generates a damaging shock wave that can be several hundred atmospheres in pressure. Fluid-filled organs such as the bladder, heart, and bowel can be burst by the pressure.
Recovery of bullets can be a very useful part of forensic ballistics. A variety of bullet designs exist, some that are specific to the firearm. Furthermore, the scouring of a bullet's surface as it encounters the grooves of the firearm barrel can produce a distinctive pattern that enables a bullet to be matched with the firearm. A weapon recovered from a suspect can be test fired and the bullet pattern compared with a bullet recovered from the scene to either implicate or dismiss involvement of the firearm in the crime.
This aspect of ballistics was crucial in convicting John Allen Muhammad and John Lee Malvo of the 10 sniper murders and the wounding of three others in the Washington, D.C. area that occurred during three weeks in October of 2002.
SEE ALSO Bullet lead analysis; Bullet track; Crime scene investigation; Gunshot residue; Firearms.