Ballistics Chapter 15

The Beltway Snipers page 506 Read the Beltway Snipers on page 506 from textbook. In an outline answer the 5 W’s. Who were they? What did they do? Where did it happen? When did it happen? Why did they do it?

Firearms Examiners Ballistics expert: -study bullets -gun operation -serial numbers -gun powder residue -shooting distance. - Forensic firearms examiners – are involved in crimes involving shootings or projectiles Ballistics - the science of the mechanics that deals with the flight, behavior, and effects of projectiles

Classification of guns Handguns – Held in one hand Revolvers - a handgun having a rotating chambered cylinder for holding a number of cartridges, which may be discharged in succession without reloading. Semiautomatic pistols – Fire once when trigger is depressed Machine pistols – Fire continously as long as the trigger is depressed

Shotgun - a smooth bore gun for firing small shot Rifles - a shoulder firearm with spiral grooves cut in the inner surface of the gun barrel to give the bullet a rotatory motion and thus a more precise trajectory. Shotgun - a smooth bore gun for firing small shot Shot is smaller beads inside a cartridge that dispersed in a circular pattern

The Gun Barrel The inner surface of the barrel of a gun leaves markings on a bullet which are unique to each gun. Rifling are the spiral grooves formed in the bore of firearm barrel which create spin on a bullet.

The surfaces of the original bore remaining between the grooves are called lands.

Determining Caliber Caliber is the diameter of the bore of a rifled firearm. Measured in hundredths of an inch or millimeters EX: .22 caliber or 9mm

Comparisons Firing Pin Impressions—the base of the casing shows where the firing pin struck which helps ID the type of gun Breechblock patterns are created in the back of the firing wall when the bullet casing is forced against the back of the breechblock leaving an impression on the casing

Comparing Ballistic Evidence The FBI maintains a database known as the General Rifling Characteristics File to help with land, groove, and twist characteristics of known weapons. Databases of information assist in ballistic fingerprinting

Ballistics Databases Bureau of Alcohol, Tobacco, and Firearms (BATF) DRUGFIRE was developed by the FBI to focus on shell casings and bullet striation patterns The Integrated Bullet Identification System (IBIS) maintained by the BATF to match bullets or casings found at crime scenes.

Gunpowder Residue Chemicals and particulates from explosive gases released when a weapon if fired are called gunshot residue (GSR) GSR clings to the shooter’s hand, arm, and clothing or other close surfaces.

Infrared photography can reveal GSR A Griess test may reveal patterns of GSR Photographic paper is pressed over the area and immersed in a reagent that reacts with inorganic nitrates in the GSR

Distance Determination Distance Determination is the process of determining the distance between the firearm and a target, usually based on the distribution of powder patterns or the spread of a shot pattern. Often test firings are made at different distances to compare residue patterns on test garments to those found on the victim.