Firearms and Tool marks

Firearms identification

Determining if a bullet came from a specific weapon.

Single-shot pistols

Fire one round at a time only.

Revolvers

Feature multiple firing chambers in a cylinder.

Swing-out revolvers

Cylinder swings out for loading and unloading.

Break-top revolvers

Top breaks open for cartridge access.

Solid frame revolvers

Fixed frame design, no break or swing.

Semi-automatic pistols

Removable magazine, fires one shot per trigger pull.

Long guns

Includes rifles and shotguns, various firing mechanisms.

Shotgun ammunition

Contains multiple ball-shaped projectiles called slugs.

Choke of the shotgun

Narrowing of barrel to concentrate shot.

Rifles

Feature lands and grooves in the barrel.

Gun barrel markings

Unique markings left on bullets by the barrel.

Rifling

Process of impressing grooves in a barrel.

Lands

Surfaces remaining between the grooves in a barrel.

Caliber

Diameter of the gun barrel between opposite lands.

Striations

Fine lines in the barrel creating individual characteristics.

Grooves

Guide bullets through the barrel, imparting spin.

Bolt-action long gun

Uses a bolt mechanism for loading and firing.

Semi-automatic long gun

Uses firing energy to load next round.

Broaching

Cutting all grooves in one pass for rifling.

Button rifling

Pressing grooves onto the barrel with a tool.

Hummer forging

Using a mandrel to create rifling patterns.

Striation Markings

Unique grooves on bullets from rifled barrels.

Class Characteristics

General features used to eliminate bullet sources.

Individualization

Identifying a bullet's unique striations for matching.

Shotgun Barrel

Smooth barrel; fires unmarked lead balls or pellets.

Gauge

Measurement of shotgun barrel diameter; higher means smaller.

Firing Pin

Strikes primer to ignite gunpowder in firing process.

Breechface

Surface that impresses markings on cartridge cases.

Cartridge Case

Holds bullet; marked by firing pin and breechface.

Ejector Mechanism

Ejects spent cartridge cases after firing.

Extractor Mechanism

Removes cartridge cases from the chamber.

Computerized Imaging

Stores bullet characteristics like fingerprint databases.

NIBIN

Database linking bullets to multiple crime scenes.

Gunpowder Particles

Residues expelled when a firearm is discharged.

Distance Determination

Assessing firing distance via powder residue patterns.

Discharge Residues

Particles from gunpowder deposited on targets.

Test Patterns

Controlled shots fired to compare with crime scene evidence.

Microscopic Methods

Traditional techniques for final bullet comparisons.

Comparison Microscope

Instrument for examining bullets side by side.

Firing Mechanism

Components that enable the gun to discharge.

Spent Cartridge Case

Used casing after bullet is fired.

Lead Balls

Projectiles fired from shotguns without markings.

Firearm Examination

Analyzing firearms and ammunition for forensic purposes.

Distance Determination

Estimation of shot distance from evidence patterns.

Stellate Tear Pattern

Star-shaped tear around bullet hole from close shots.

Vaporous Lead Halo

Smoke ring indicating discharge within 12-18 inches.

Powder Grains

Unburned particles observed up to 25-36 inches distance.

Bullet Wipe

Dark ring around hole from shots over 3 feet.

Gunpowder Residue

Residue examined for distance and weapon identification.

Shotgun Distance Estimation

Spread of shot indicates muzzle-to-target distance.

Greiss Test

Chemical test for detecting invisible gunpowder residues.

Primer Residue

Residues on shooter's hands indicating weapon discharge.

Barium and Antimony

Elements measured to confirm gunshot residue presence.

Adhesive Stubs

Tools used to sample gunshot residue from hands.

Microscopic Examination

Initial analysis for gunpowder residue on evidence.

Contact Shot

Shot fired with weapon touching the target.

Distance Patterns

Test patterns made at specific distances from target.

Criminalist

Forensic expert restoring obliterated serial numbers.

Serial Number Restoration

Process of recovering removed or damaged serial numbers.

Evidence Patterns

Visual indicators used to determine shooting distance.

Discharge Residues

Residues blown back toward shooter during firing.

Soot Presence

Indicates proximity of weapon to target.

Pellet Spread

Separation of pellets increases with distance from target.

Infrared Photography

Technique to enhance visibility of powder stains.

Microscopic Analysis

Detailed examination for gunpowder residue identification.

Chemical etching

Restores serial numbers on metal surfaces.

Firearm evidence collection

Process of gathering firearms for analysis.

Trigger guard

Part of firearm held during collection.

Chain of custody

Documented history of evidence handling.

Revolver chambers

Holds cartridges; must be recorded upon recovery.

Evidence container

Properly labeled packaging for crime scene evidence.

Striation markings

Unique patterns on bullets from firearm barrels.

Tool mark

Impression made by a tool on another object.

Class characteristics

General traits of a tool or impression.

Individuality in tools

Minute imperfections that distinguish one tool.

Comparison microscope

Instrument for comparing tool marks and impressions.

Evidence integrity

Maintaining evidence quality during investigation.

Impression photography

Capturing details of impressions with scale.

Casting

Method to preserve shoe and tire marks.

Chemical enhancement

Visualizes latent blood impressions at crime scenes.

Points of comparison

Unique features supporting source identification.

Shoe print comparison

Analyzing footwear impressions for evidence.

Bite mark impressions

Evidence from skin or food in crimes.

Accidental discharge precautions

Safety measures before handling loaded firearms.

Packaging bullets

Wrap in tissue before placing in containers.

Tool mark examination

Analyzing impressions for forensic evidence.

Transporting evidence intact

Preserving evidence by moving it without alteration.