ballistics

Forensic ballistics

Study of firearms, bullets, and impacts in crimes

Firearm identification

Linking bullets/cartridges to a specific firearm

Types of ballistics

Internal, External, Terminal

Internal ballistics

What happens inside the firearm

External ballistics

Bullet flight through the air

Terminal ballistics

What happens when bullet hits target

Bullet flight path

Parabolic due to gravity

Point blank range

Distance where bullet stays flat enough to hit directly

Bore angle

Angled slightly upward to cross line of sight

Ballistic coefficient

Measures air drag effect on bullet flight

Aerodynamic drag factors

Velocity, bullet shape, air/weather

Drag coefficient

Number showing air resistance on bullet

Cartridge/Round

Bullet + powder + primer in a metal case

Bullet

The projectile part of a round

Blank

Cartridge with no bullet, only sound

Dummy

Inert round that cannot be fired

Caliber

Bullet diameter (in inches or mm)

Firing sequence

Trigger → pin hits primer → powder ignites → bullet fires

Toolmarks

Breech marks, firing pin, extractor/ejector marks

Breech face

Part pressing against cartridge during firing

Firearm evidence

Gun, bullets, cartridge cases, shot shells, wadding, ammo, clothing

Ballistics expert tasks

Analyze firearms, toolmarks, trajectory

Key tool used

Comparison microscope

Revolver check

Note fired & unfired rounds

Automatic check

Count rounds in magazine, fingerprint it

Firearm collection

Ensure unloaded, don’t insert objects, tag trigger

Shotgun shell clues

Casing/wadding show gauge, manufacturer, marks

Bullet Comparison

Test bullets fired from suspect gun and compared

Comparison Microscope

Used to match striations on bullets

Milling Marks

Microscopic drill marks inside barrel; unique to each gun

Bullet Impact

Bullets may fragment or mushroom on impact

Rifling

Spiral grooves in barrel to spin bullet

Lands

Raised parts between grooves in rifling

Ballistic Fingerprinting

Unique marks from manufacturing and wear

Gross Differences

E.g. 10 mm bullet won't fit 9 mm barrel

Striations

Fine grooves on bullet from rifling

Striations - Class

Shared by same gun type

Striations - Individual

Unique to one specific gun

Firing Pin Marks

Impressions left by firing pin

Chamber Marks

Can vary due to rust, grit, or bullet deformation

Bullet Weight

Can suggest gun make

Microgrooves

Rifling with 8–24 fine grooves

General Rifling Characteristics File

FBI database of land/groove widths

Bullet Shape

E.g. Wadcutter = flat front, full lead

Wadcutter Use

For target shooting; not good for long range or semi-autos

Wadcutter Pros

Clear holes on target, good for training

Ammunition Types

Lead, semi-jacketed, full metal jacket

Lead Bullets

Scraped by rifling; softer

Semi-Jacketed

Jacketed sides, exposed tip; expands on impact

Full Metal Jacket

Lead core fully covered; less expansion

Gunshot Residue (GSR)

Particles from firing a gun

GSR Sources

Hands, clothing, target, gun barrel

GSR Elements

Lead, barium, antimony

GSR Detection

Swab hand, test for nitrates

Griess Test

Detects nitrites (explosives); pink = positive

GSR - False Negatives

Washed hands, gloves, or lead-free ammo

GSR - Rifles/Shotguns

May not deposit GSR on hands

Firearms Evidence

Guns, bullets, casings, shells, wadding, clothing

Firearms Exams

Bullet markings, caliber, GSR, shot pattern

Matching Bullets

Compare firing pin, ejector, breechblock marks

Evidence Handling

Wrap bullets, never insert tools into barrel

Revolvers

Note position of fired/unfired rounds

Automatics

Count magazine rounds, tag trigger guard

Drugfire

FBI’s ballistic evidence database

FTU

FBI Firearms-Toolmarks Unit

IBIS

National database of bullet/casing markings

IBIS - Bulletproof

Bullet markings software

IBIS - Brasscatcher

Cartridge case software

IBIS Function

Match forensic images to database entries

Gun Types

Semi-auto, revolver, rifle, shotgun

Bullet Types

Full metal, soft point, hollow point, lead alloy

Cartridge Marks

Firing pin, breechblock, ejector, extractor

Vaporific Effect

Flash fire from high-velocity impact

Flash Fire

Burns particles from projectile or target

Dust Explosion

From pyrophoric metal + air in enclosed spaces