A Simplified Guide To Firearms Examination

Introduction

Forensic firearms examination involves identifying whether a bullet or cartridge case was fired from a specific firearm.
This is based on unique microscopic markings left on bullets or cartridge cases by the firearm.
While it doesn't identify the shooter, matching ammunition to a weapon is crucial for investigations.
Examiners also explain firearm functions and safety features, important in cases of suicide, unintentional shootings, and accidental discharges.

Firearms have unique microscopic irregularities that transfer to cartridge cases and bullets when fired.
Examining these markings helps identify or exclude a firearm in a crime.
The primary tool for this examination is the comparison microscope.

Characteristics include caliber, grooves, and their twist direction in the barrel.
Spiral grooves in barrels stabilize bullet flight, leaving specific impressions on bullets.
Polygonal rifling by some manufacturers may complicate assessments.

Firearms evidence can be found at crime scenes involving shootings, including murders and robberies.
Key evidence includes bullets, cartridge cases, and gunshot residues.
Examiners analyze evidence to identify the type of firearm used and compare evidence from different scenes.
Functional testing of recovered firearms checks for proper operation and safety features.

Evidence can range from small bullet fragments to multiple firearms.
Analysis may involve comparing shotshell wads or gunshot residues to determine shooting details.
Evidence collection should maintain integrity, often involving careful extraction from surfaces.
A trained firearms examiner conducts the analysis, using tools like comparison microscopes and test-firing facilities.

Firearms examination results include identifying whether a bullet/cartridge was fired by a particular firearm.
Limitations arise from damaged evidence or lack of a suspect firearm.

Laboratories follow strict procedures to ensure accurate analysis, including accreditation and technical reviews.
Cross-examination and independent reviews further ensure accuracy.

The Frye and Daubert standards guide admissibility of scientific evidence and expert testimony.
Expert witnesses must be qualified and skilled, often determined by court rulings like Frye and Daubert.

Ballistics: Study of projectile motion.
Bullet: Projectile expelled from a firearm.
Cartridge: Complete unfired ammunition round.
Comparison Microscope: Primary tool for side-by-side examination of evidence.
Individual Characteristics: Unique firearm marks on ammunition.
Rifling Grooves: Interior barrel grooves that impart spin on bullets.
Shotgun: Firearm with a smooth barrel, usually shoulder-fired.

Key resources include AFTE, NIBIN, and SWGGUN for further learning.
Notable publications and experts contribute to the body of knowledge in firearms examination.

This guide serves as an educational resource for understanding forensic firearms examination, key principles, and relevant legal standards.