INTRODUCTION

Firearms Identification is a discipline of Forensic Science that has as its primary concern to determine if a bullet, cartridge case, or other ammunition component was fired from a specific firearm.


FIREARMS IDENTIFICATION

Whenever a shooting occurs the firearms evidence is collected and evaluated as to its importance to the case. The evidence submitted to a lab's Firearms Section will typically include a firearm or firearms, fired bullets, spent cartridge cases, spent shotshells, shot, shotshell wadding, live ammunition, clothing. The role of the firearms examiner is to perform specific scientific examinations upon the evidence submitted using various tools and instruments. One of the most common examinations conducted by the firearms examiner involves trying to determine if a submitted firearm fired the bullet removed from the body of a shooting victim or fired spent cartridge cases found at the scene of a shooting incident. Firearms identification involves a great deal of comparative analysis. The firearms examiner will compare ammunition components to each other for common characteristics or similarities. When making such comparisons the firearms examiner will first look for similarities !
called class characteristics

CLASS CHARACTERISTICS

Class characteristics are those that would be common to a particular group or characteristics that were designed into the make-up of a group of items. To determine if a particular bullet was fired from a specific firearm you must first know if the questioned bullet shows class characteristics consistent with those that would be produced by the suspect firearm. The class characteristics of firearms that relate to the bullets fired from them includes the caliber of the firearm and the rifling pattern contained in the barrel of the firearm.

CALIBER

When a bullet is submitted for examination one of the first examinations conducted will be to determine the bullet's caliber. Caliber is a term used to indicate the diameter of a bullet in "hundredths of an inch". A bullet that is 32 hundredths of an inch (.32) in diameter is called a 32 caliber bullet. The term caliber is of English origin and is a term commonly used by arms manufacturers in the United States. Firearms and ammunition of European origin use the metric system and would refer to a 32 caliber bullet as an 8mm bullet. Now, the 32 caliber bullet can vary in length, weight, and appearance. These factors as well as the type of cartridge case used with the bullet help determine what the cartridge designation will be. Examples of different 32 caliber cartridges are 32 Long Colt, 32 Smith & Wesson, and 32 AUTO. If the caliber of the bullet submitted for examination matches the caliber of the submitted firearm the firearms examiner will look for additional class chara!
cteristics in the form of rifling.

RIFLING

Most handguns and rifles have rifled barrels. Rifling consists of grooves cut or formed in a spiral nature, lengthwise down the barrel of a firearm. The rifling in a barrel will grip bullets as they travel down the barrel. The spiral or twist to these grooves will impart a spin on the bullet. Because bullets are oblong projectiles they must spin (like a thrown football) in their flight to remain accurate. The whole point to this is that different firearms can have different patterns to their rifling. A firearm may have a six grooved barrel with the grooves twisting to the left where another firearm's barrel may have eight grooves that twist to the right. When a bullet travels down the barrel of a firearm the rifling will impart its negative impression on the sides of the bullet. When a bullet is submitted for comparison to a firearm it must not only match in caliber but the rifling impressions on the bullet must match the rifling pattern found in the barrel of the firearm. !
If both of these class characteristics match between the bullet and firearm then the firearms examiner will look for what are called individual characteristics.


INDIVIDUAL CHARACTERISTICS

Individual characteristics are those characteristics that are unique to an item. It's the ability for one item to transfer individual characteristics to another that makes firearms identification possible. Firearms Identification is based on the principle that any two objects that come into contact with each other can cause the softer of the two objects to be marked by the harder object. When a bullet travels down the barrel of