Introduction

Throughout the nineteenth century, many developments took place. One of these- ballistics- is the study of the functioning of firearms- firing, the flight of the bullet, and the effects of different types of ammunition. Ballistics in crime investigation was first formally established in 1923 when Charles Waite and Philip Garavell set up the bureau of Forensic Ballistics (BFB). Later, Colonel Calvin Goddard joined the team and together they developed their own specialized equipment. Their most important development was the comparison microscope. It contained an optical bridge which allowed two objects to be compared.

From Crime Scene to Lab

At the scene of a crime, police look for bullets and spent cartridge cases. When police find a suspect’s weapon, lab technicians take the gun and fire test bullets from the gun into a cotton wall or a water tank. Under a microscope, the technician can compare the striations on the test bullets with the marks on the bullet from the crime scene. He looks for the direction and degree of the twist, the depth of the grooves, and any imperfections. If the two bullets match, they are from the same gun.

The lab also examines spent cartridge cases. Every gun’s firing pin hits the primer (or firing cap) in an unique way. Its breech face (the rim that holds the cartridge in the chamber) leaves unique markings. The ejector rod, which discharges the spent casing from the chamber, also leaves distinctive marks as well. The lab can use these marks to determine whether the spent cartridge case came from the suspect’s gun.

Ballistic science can also be used to determine whether or not a person was present when a gun crime was committed. When a gun is fired, tiny specks of primer residue and gunpowder remain on the hand of the person who fired it. The police take residue samples from the suspect’s hands, and a lab analyzes the samples for traces of the chemicals antimony, barium, and lead.

Bullets and Cartridges

When a criminal fires a gun, clues will be left. A bullet from a spent cartridge can be traced to the gun. This is possible is because of the basic design of firearms. When a gun is made, a hole is drilled in the barrel for the bullet to travel through. The barrel of the gun has ridges, or rifling to make the bullet spin- much like when throwing a football, the bullet spins in order to increase accuracy. When a bullet is fired and travels down the guns barrel, the spiral rifling cuts markings into the bullet. These grooved markings are called striations. The striations from one gun will differ from those caused by any other gun.

Trajectories

Calculating the trajectories or path of the bullets can help police and detectives determine what happened at the crime scene. Trajectories can be calculated in a number of ways. In its simplest form in a relatively enclosed space, provided the positions and alignment of the gun is known, a straight line can be drawn along the bullet’s projected flight path to the place where the bullet was found. Crime scene detectives usually mark supposed and actual trajectories with lengths of string. Small hand-held lasers can be used as well.

 

Information from

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