Ballistics

Ballistics is the science that deals with the impact, path, and velocity of

projectiles. Some people say ballistics is the science of projectiles in motion. There are

several different issues while discussing ballistics. Bullet characteristics and comparison

is the first thing. Another issue is the study of terminal, transitional, interior, and exterior

ballistics. The next issue is the instruments used to study the weapon and or bullets in

question and how they test them. After that is the way the court uses ballistics for trials

as well as the experts who determine similarities in the weapons or bullets used in the

crime.

There is some basic terminology of bullet comparisons. Lands is the term gun makers use to represent the original hole size. Grooves are impressed onto the inner surface of a gun barrel to guide and spin the bullet. Grooves are also called riflings. The grooves may twist right or left and the number varies greatly from gun to gun. The grooves are cut with a rifle cutter which is a sharp edged tool with fine saw-like teeth only visible with a microscope. The rifle cutter makes small scratches on the steel inside the barrel while making the grooves. Striations are the imperfections inside the barrel running the full length of the barrel's lands and grooves. Just like fingerprints no two barrels are identical. The caliber is the measure between lands (diameter). The caliber can be measured in two ways. The first way is measured in hundredths of an inch, for example a .22 or .38. The second way the caliber is measured is by millimeters, for example a 9mm or 45mm. When a bullet passes through a barrel the surface is impressed with the rifled markings of the barrel.

Ballistics is divided into four categories, transitional, interior, and exterior

ballistics. Interior ballistics includes the features of chamber design, density or loading,

pressures, and powder chemistry. Interior ballistics covers everything that occurs within

the bore of the gun during the period that elapses between the discharge of the firing pin

strikes the primer of the cartridge and the emerging of the projectile from the muzzle,

regardless of the type of gun. Also the interior ballistics calculates the velocity,

breech and base pressure, linear and angular accelerations of the projectile during travel

down the barrel. Exterior ballistics studies the physical phases the projectile

or bullet passes through in its flight from muzzle to target or final point of impact.

Transitional ballistics, also known as intermediate ballistics, is the study of a projectile's

behavior from the time it leaves the muzzle until the pressure behind the bullet is

equalized, so it lies between interior, and exterior ballistics. Terminal ballistics, a sub-

field of ballistics, is the study of the behavior of a projectile when it hits its target. It is

often referred to as stopping power when dealing with human or other living targets.

Terminal ballistics is as relevant for both small caliber projectiles as for large caliber

projectiles.

Factors in the bullet's flight are: atmospheric friction; gravity, causing a fall of the bullet toward the earth; rotational velocity or spin, controlled by the pitch or twist of the rifling which has a direct influence on accuracy; and the initial velocity of the projectile itself, its shape, and sectional density.

Bullet velocity and mass will also affect the nature of wounding. Velocity is

classified as low, medium, and high. An m-16 rifle is designed to produce large surface

wounds with high velocity and low mass bullets.