FRSC1030 Foundations of Forensic Science Chapter 16

Breech face marks

Marks that result when the cartridge is fired and the casing is forced backwards, impacting the breech face.

Caliber

The term that refers to the size of cartridges used in firearms, originally referring to the diameter of the barrel of a rifle or a pistol, measured from the top of the lands and given in hundredths or thousandths of an inch or millimeters. 

Cartridge

A self-contained unit of ammunition, sometimes called a round or a load, consisting of four components: the bullet, the propellant, the primer, and the case.

Centerfire

A type of cartridge, in which the primer cap is placed in the center of the cartridge base, used in most modern handguns, rifles, and shotguns, because the central primer is more powerful and reliable than the primer found in rimfire cartridges.

Chemical etching

A process that used corrosive chemicals to reveal obliterated serial numbers and other marks on metal objects by selectively dissolving the metal surface. The damaged areas of the metal will dissolve faster than the non-damaged material, so they will reveal the serial number.

Comparison microscope

The instrument used to study firearms, consisting of two microscopes connected by an optical bridge that allows the examiner to adjust and align the separate images for direct comparison.

Compression tool marks

Marks that are a result of when a tool is pressed into a softer material, as with bullet markings. 

Consecutive matching striations (CMS)

An approach used in firearm and toolmark analysis to establish a numerical criterion for determining if two striated toolmarks were produced by the same tool.

Cutting tool marks

Marks that are combinations of compression and sliding tool marks.

Distance determination

Also called distance estimation, a test that determines the distance between a gun and a target surface using a series of experiments in which the gun is loaded with ammunition as similar to that in the case as possible, shot at known distances at targets that mimic case samples.

Double action weapons

Firearms that rotate the cylinder and bring the hammer down on the cartridge with a single trigger pull. 

Ejector

The part of the gun that pushes out a fired cartridge case out of the firearm.

Ejector marks

Marks created on cartridge cases by the metal-to-metal contact between the cartridge case and the ejector mechanisms in a firearm.

Firing pin

Also called a striker, he component of a firearm that strikes the primer of a cartridge, causing it to ignite and fire the bullet.

Gauge

The number that describes how many lead pellets of a given size were needed to reach one pound. For example, a 12-gauge shotgun would have pellets that weighed 1/12th of a pound, and a 20-gauge would have 1/20th of a pound pellets. The bigger the gauge, the smaller the barrel and the bigger the shot.

Ghost guns

Guns made by a manufacturer that never registers them, such as when they are 3D printed, which makes them very difficult to trace. 

Hammer

The component of a firearm that, when cocked, rotates the cylinder to place one of the chambers under it, and cocks the firing mechanism.

Headstamp

The markings on the bottom of a cartridge case, usually showing who manufactured the case.

Integrated Ballistic Identification System (IBIS)

An automated image collection system designed for firearms evidence.

Lands and grooves

A series of grooves cut into the barrel of a gun at an angle, which can be used as class characteristics.

Long guns

Rifles and shotguns, designed to be held in two hands when being fired from the shoulder, with many subcategories such as semiautomatics, lever actions, and bolt actions.

National Integrated Ballistic Information Network (NIBIN)

An american database that holds firearm-related images of markings such as those on bullets and firing pins.

Primer

The component of a firearm that when striked by the firing pin, initiates the firing sequence by igniting the propellant powder.

Propellant

A chemical that rapidly burns to produce high-pressure gases that propel a projectile from a firearm, such as nitrocellulose-based smokeless powders or black powder.

Revolver

A handgun with at least one barrel and a revolving cylinder containing multiple chambers for firing.

Rifling

A series of lands and grooves cut into the barrel at an angle that the hot bullet conforms to, and in turn acquires spin as it twists down the barrel, essential for accuracy.

Rimfire cartridges

Cartridges with a primer composition in the rolled rime of the cartridge, fired by the weapon’s firing pin striking the cartridge rim.

Serial number restoration

The process of restoring a serial number stamped into a metal surface using chemical and electrochemical methods.

Shooting reconstruction

The process of reconstructing a shooting using physical evidence, to understand the sequence of events during the incident, such as the path and trajectory of the bullet, the distance from the firearm to the target, the number of shots fired, etc. 

Single action revolvers

Revolvers that are fired by manually cocking the hammer and then pulling the trigger.

Slide

The component of a firearm that is driven backwards by the energy produced by the fired cartridge, extracting the spent cartridge from the chamber, ejecting it from the weapon, and cocking the firing mechanism.

Sliding tool marks

Marks that result when a tool slides along a surface, usually consisting of parallel striations. 

Striations

A pattern of lines, grooves, or scratches on the surface of something, examined to determine the similarities and differences between two samples, such as bullets.

Twist angle

The angle at which a barrels grooves twist, making the bullet spin as it is fired out of the firearm. 

Wear characteristics

Characteristics on a surface resulting from wear and tear or constant usage.