Firearms Identification Types, Function, ballistics and trajectory

Firearms identification Includes: Comparison of bullets Operation of all types of weapons Restoration of obliterated serial numbers Detection of gunpowder residue on clothing and hands Estimation of muzzle-to-target distances

Bullet comparisons Rifling – the creation of spiral grooves on the inside of a gun barrel when it is drilled Bore – the interior of a gun barrel Lands – the raised parts of the barrel between the grooves Grooves – the cut out channels between the lands

Rifling characteristics

Rifling Process History of Rifling https://www.youtube.com/watch?v=VbOt-y0oI68 Present Day Method https://www.youtube.com/watch?v=oALJDh43K3I

Rifling methods Broach cutter – series of concentric steel rings, each slightly larger than the next simultaneously cuts all grooves in a barrel Rotates as it cuts, giving the appropriate direction (left or right) and rate of twist

Rifling Methods Every manufacturer develops caliber specific rifling for optimal bullet performance Rifles will have larger twist rates than pistols Rifles will have 1/12, 1/10, 1/8 Pistols will have similar rates of twist, however, the barrels are so short, the benefits are never realized

Rifling methods Button – a steel plug impressed with the desired number of grooves; no cutting involved – the button is forced under high pressure through the bore, compressing the surface Mandrel – similar to a button; inserted into oversized barrel, then barrel is hammered to acquire the impressions

Rifling examples: .32 caliber Smith & Wesson revolvers - 5 lands and grooves with a right-hand twist Colt .32 revolver – 6 lands and grooves to the left 9MM is 1/8” .22 caliber is anywhere from 1/8”-1/16”

Bullet comparisons Caliber – the diameter of the bore of a rifled firearm; Expressed in hundredths of an inch or in millimeters

Class vs. individual characteristics Each gun manufacturer chooses a rifling pattern, giving their guns a class characteristic Each gun barrel is bored and rifled, with minute differences, giving each firearm individual characteristics Even after hundreds of firings, bullets can still be matched to a unique gun

Calvin Goddard (1891-1955) Publishes “Forensic Ballistics” in 1925 Discusses how bullets can be identified by their unique markings under a microscope. Became known nation wide for using these techniques to convict Sacco and Vanzetti FBI is pushed to adopt his practices

Ballistics Ballistics the science of projectiles and firearms. The study of the effects of bullets being fired from a gun. Knowledge of chemistry, physics, trigonometry, and 3D design are essential As well as Mass, Velocity, and deceleration

Bullet Design Bullet design has everything to do with accuracy and trajectory