Chapter 9: Firearms, Tool marks, and other impressions

Firearms

Weapons designed to expel projectiles, typically bullets, through a tube by means of an explosive charge.

Rifling

The process of impressing spiral grooves into the interior of a gun barrel, which imparts spin to a bullet.

Class Characteristics

Features that are common to a group of items, such as guns of the same make or model.

Individual Characteristics

Unique marks or patterns that can be attributed to a specific object, allowing for individualization.

Cartridge Case

The part of a shotgun or firearm that holds the bullet, gunpowder, and primer.

Breechface

The rear part of a firearm barrel that contacts the cartridge case during firing.

Caliber

The diameter of the inner barrel of a firearm, often expressed in inches or millimeters.

Choke

An interior constriction placed at or near the muzzle end of a shotgun barrel to control shot dispersion.

Greiss Test

A chemical test used to detect and develop gunpowder residues on surfaces.

Ejector

A mechanism in a firearm that throws the cartridge from the chamber after firing.

Extractor

The mechanism in a firearm that withdraws a cartridge from the chamber.

Comparative Microscope

An instrument that allows two bullets to be compared side by side under magnification.

NIBIN

National Integrated Ballistics Information Network, a program that allows law enforcement to compare ballistic evidence electronically.

Ballistics

The study of the dynamics of projectiles and their behavior when fired.

Tool Marks

Any impression, cut, gouge, or abrasion caused by a tool coming in contact with another object.

Restoration of Serial Numbers

The process of recovering obliterated serial numbers on firearms through chemical means.

Shotgun

A type of long gun designed to fire a spread of small lead pellets or a single projectile.

Handgun

A firearm designed to be fired with one hand, such as a pistol.

Revolver

A type of handgun with a revolving cylinder containing multiple chambers for bullets.

Semiautomatic Pistol

A handgun that fires one bullet with each pull of the trigger and automatically chambers the next round.

Automatic Firearm

A firearm that continues to fire as long as the trigger is held down.

Firing Pin

A small metal rod that strikes the primer of a cartridge to initiate firing.

Muzzle

The end of the barrel from which the bullet exits.

Gas Operation

A mechanism in semiautomatic firearms that uses the energy from gunpowder gases to cycle the action.

Test Firing

Discharging a firearm to obtain bullets for comparison with evidence.

Wad

A component of shotgun shells that separates the shot from the powder and seals the shell.

Striation Markings

Fine lines on bullets that result from the rifling in the barrel, unique to each firearm.

Microgrooving

A technique of rifling in which numerous small grooves are cut into the barrel.

Gauges

The measurement used to specify the diameter of shotgun barrels.

Handgun Types

Different categories of handguns including single-shot, revolvers, and semiautomatics.

Gunpowder Residue

Particles left on a shooter's hands or clothing after firing a weapon.

Distance Determination

The process of estimating how far a firearm was from a target when discharged.

Nitrate Test

A method for detecting unburned gunpowder residues on hands.

Ammunition

The projectile, along with its casing and propellant, used in firearms.

Case Markings

Impressions left by the firing mechanism on the cartridge case.

Ballistics Fingerprinting

The concept of cataloging the unique ballistic marks left by firearms.

Impression Evidence

Marks left at a crime scene that can link a suspect to a crime.

Tire Impressions

Marks left by a tire that can provide evidence related to vehicle movements.

Footwear Impressions

Marks left by shoes that indicate a person's presence at a crime scene.

Serial Numbers

Identification numbers stamped on firearms for tracking and identification.

Preservation of Evidence

Protocols for maintaining the integrity of physical evidence collected from crime scenes.

Microscopic Examination

Use of microscopes to analyze minute evidence for individualization.

Swabbing Technique

A method for collecting residues from hands by using moistened cotton.

Plastic Impressions

Impressions made in a soft material, such as mud or wax, that captures detail.

Chemical Enhancement

Using chemicals to visualize faint marks or patterns on evidence.

Electrostatic Lifting

A technique used to lift dust impressions using static electricity.

Casting Techniques

Methods used to create three-dimensional replicas of impressions.

Controlled Substances

Drugs that may be tested for residue presence during investigation.

Sample Extraction

Process of obtaining sample residues from suspected shooters.

Individualization Techniques

Methods used to link specific evidence to an individual or object.

Criminalistics

The application of science to solve crimes, especially through physical evidence.

Comparative Analysis

Examining and comparing evidence to establish links or differences.

Non-Destructive Testing

Methods used to examine evidence without altering its condition.

Firing Distance Assessment

Determining the proximity of a shooter to the target based on residue patterns.

Breech Markings

Unique patterns left on cartridge cases by the breechface.

Soot Ring

A dark circle around a bullet hole indicating close-range fire.

Bullets Recovery Method

Techniques for safely extracting fired bullets for analysis.

Forensic Identification System

Databases that help in matching bullets and cartridges to crimes.

Characterization of Firearms

Classifying firearms based on design, operation, and other features.

Trace Evidence

Small amounts of material transferred from one surface to another during a crime.

Photomicrography

Using photographs to document microscopic evidence.

Firearm Examiner

A forensic specialist who analyzes ballistic evidence.

Marking Safety Protocols

Guidelines for labeling and identifying evidence collected from crime scenes.

Rifled Barrel

A barrel with grooves cut into it to stabilize a bullet as it is fired.

Laboratory Analysis

Testing procedures performed to evaluate evidence scientifically.

Evidence Chain of Custody

Documented process that tracks the handling of evidence.

Physical Evidence Collection

The systematic gathering of artifacts related to a crime.

Minimal Disruption**

Handling of evidence in ways that preserve its original condition.

Forensic Documentation

Record keeping related to forensic evidence and investigations.

Marking Procedures

Methods for designating identification information on collected evidence.

Comparison Standards

Baseline samples used for evaluating suspected evidence.

Research and Development

Ongoing efforts towards improving forensic analysis technologies.

Bullet Identification

The process of linking bullets to specific firearms through analysis.

Assessment Techniques

Methods used to evaluate and conclude on evidence.

Prevention of Evidence Tampering

Protocols in place to safeguard against alteration of evidence.

Tangible Evidence

Physical objects collected during investigations.

Scientific Method in Forensics

Applying scientific principles to gather and analyze investigative evidence.

Review Questions

Follow-up inquiries meant to assess understanding of forensic concepts.

Preparation for Expert Testimony

Ensuring readiness to present forensic findings in legal proceedings.

Procedural Guidelines

Established practices for undertaking forensic investigations.

Key Forensic Terminology

Essential vocabulary used in the field of forensic science.

Ethics in Forensics

Moral principles governing the conduct of forensic professionals.