General Considerations of Firearms Identification and Ballistics (From Medicolegal Investigation of Death, P 202-215, 1980, by Werner U Spitz and Russell S Fisher - See NCJ-69730)

• NCJ Number: 69735
• Author(s): R M Wilhelm
• Date Published: 1980
• Length: 14 pages
• Sale Source: Charles C. Thomas
• Language: English
• Country: United States of America

Annotation

Characteristics of firearms and bullets and methods of identification, as presented in a forensic pathology text, are discussed; class and individual firearms characteristics are emphasized.

Abstract

A firearm is defined as any instrument or device with which it is possible to propel a projectile by means of the expansive force of gases generated by the combustion of an explosive substance. Firearms originally fired round balls from smooth bore arms. The transition to modern rifling was motivated by the desire for greater sectional density with less resistance to the air. The science of firearms identification is based on the premise that it is impossible to make any two articles absolutely identical. When firearms are viewed under the comparison microscope, this premise is verified. Part of the science of firearms identification is based upon variations of the inner surface striations of the barrel. The number of land and groove impressions and their approximate dimensions are termed class characteristics. Thus, a Smith and Wesson revolver of .32 caliber is designed and built to certain specifications. It has five lands and five grooves, with the direction of twist to the right. The fine striae created by the broach or hone finishing of the barrel or other surfaces of the weapon are referred to as individual or accidental characteristics. Minute chips of steel break from the broach in the process of rifling, scarring the bore with microscopic fine striae. The bullet, in its travel through the barrel, takes on this signature, which is a summation of all accidental marks. The comparison microscope is so constructed that by means of two separate microscope tubes joined by a bridge with prisms mounted over these tubes, the two images are transmitted to the center of the bridge. Comparison of the fine scratch marks of bullets allows identification of a suspected firearm. If it is the weapon used in a homicide, bullets from test firings will match those taken from the victim with regard to striations. Photographs, sketches, and a reference are included in the chapter. For related documents, see NCJ 69731-34 and 69736-47.