Introduction to Ballistics

Central Focus

• Ballistics includes the explanation of types of ballistic evidence collected, and the descriptions and interpretation of ballistic evidence through trajectory paths and bullet markings

Standards for Ballistics

• Impression evidence is analyzed to make a physical match examination
• Impression evidence includes ballistics, tool marks, footwear, tire impressions, bombings and arson.
• Forensic investigations require proper evaluation and communication of information
• Arguments are constructed from evidence, and explain the relevance of possible evidence at the crime scene
• Physical and trace evidence require the application of scientific techniques
• Chromatography and spectroscopy are scientific techniques in evidence analysis

Essential Questions for Ballistics: Day 1

• What is ballistics?
• How are guns classified?
• How are bullets classified?

Learning Targets for Ballistics

• Ballistics' role in forensic science must be explained
• How a firearm works must be explained
• Types of firearms need to be compared and contrasted
• Bullets, slugs, and shot need to be compared and contrasted

Ballistics

• Ballistics is the scientific analysis of firearms, bullets, and the travel of projectiles in flight
• A firearm is a weapon capable of firing a projectile using a confined explosive

Ballistics - Finding Details

• Ballistic experts find facts during shooting-related crimes
• Facts include: type of firearm, caliber of bullet, number of bullets fired, shooter's location, and if the weapon was used in previous crimes

History of Firearms

• The Chinese invented gunpowder over 1,000 years ago for fireworks and weapons
• Gunpowder is a mix of potassium nitrate, charcoal, and sulfur
• Gunpowder expands upon ignition, which causes a violent explosion

Matchlock Weapons

• Matchlock weapons were first firearms, and used wicks to ignite gunpowder
• The matchlock had a secured, lighted wick in a moveable arm
• When the trigger was depressed, the wick was brought down against the flash pan to ignite the powder, improving the user's steadiness

Flintlock Weapons

• Flintlock weapons used flint to ignite gunpowder
• Flintlocks improved over matchlocks by using a simple spark instead of an open flame

Muzzleloaders

• Muzzle loaders are any firearm into which the projectile and propellant is loaded from the gun’s muzzle
• Muzzleloaders were replaced by breech-loading firearms with the advent of the cartridge

Cartridges or Rounds

• A cartridge is a case holding a bullet, a small amount of exploding primer powder, and gunpowder, and is the correct name for the "entire package"
• To refer to the entire package as just a "bullet" is inaccurate: the bullet is just one of multiple components

Cartridge Components

• Primer is a volatile compound that ignites when struck by the gun’s firing pin and detonates the propellant in the cartridge
• Propellant is gunpowder that forms gases to push the bullet out of the cartridge and the gun barrel
• The casing is left behind and is not propelled with the bullet

Bullets

• A bullet is the projectile propelled from a firearm
• Bullets are made of metals like copper, lead, brass, bronze, steel, or aluminum

Bullet Compositions

• Lead bullets are cheap, dense, soft, and easy to mold
• Half jacketed bullets are lead bullets coated with copper halfway up the exposed portion of the bullet to improves exit velocity and promote mushrooming
• Jacketed bullets use a full metal jacket of copper which improves exit velocity and is used to hold the shape of the bullet in an effort to maximize penetration

Bullet Shapes

• Round-nose bullets have a blunted end for maximum penetration
• Hollow-point bullets create more damage, inhibit penetration, and spread or mushrooms on impact
• Jacketed bullets have soft lead surrounded by another metal that allows the bullet to penetrate a target more easily
• Wadcutter bullets have a flattened front, are used exclusively as a practice load, and rip a hole in target paper that’s visible by the shooter

Bullet Caliber

• Caliber is the diameter of the inside of a firearm’s barrel
• Caliber also matches the diameter of the bullet, and is usually expressed in hundredths of an inch (0.22 cal) or in millimeters (9 mm)

How a Firearm Works

• The firing pin hits the base of the cartridge, igniting the primer powder
• The primer powder sparks through the flash hole to the main propellant supply
• The pressure of the explosion pushes the bullet from the casing into the barrel
• The bullet follows lands and grooves to spiral out of the barrel

Modern Firearms

• Modern firearms include handguns and long guns

Long Guns

• Long guns require two hands for accurate shooting
• Long guns include rifles and shotguns
• Rifles fire bullets, and their barrels are “rifled” with lands and grooves
• Shotguns fire small round pellets called shots, or single projectiles called slugs; their barrels are smooth

Shotgun Shells vs Rifle or Pistol Cartridges

• All contain a case, a primer, and gunpowder
• Shotgun shells also contain a wad of plastic or fiber that separates the shot from the gunpowder
• The "shot" is comprised of small, round pellets usually made of lead or steel, and replaces the bullet
• A shotgun shell contains anywhere from 6 ball-bearing-type pieces of metal to 1,300 pellets
• A shotgun shell may contain a slug, which is a solid piece of metal
• A wad forms a seal which allows gases from the burning powder to push the shot down the barrel uniformly

Handguns

• Handguns are categorized as pistols or revolvers
• Pistols are fired with one hand
• Revolvers are a type of pistol that holds several cartridges that can be fired one after another
• Civilian firearm injuries most often come from handguns (86%), followed by shotguns (8%) and rifles (5%)
• Revolvers are usually easier for first time shooters to learn how to shoot safely because they exhibit less recoil

Grouping Handguns - Revolvers

• Revolvers have been around since the 1830s
• Revolvers hold 6 cartridges (“six shooter”) stored in a rotating cylinder
• Cocking the hammer rotates the cylinder and drops a round into the chamber, aligning it with the hammer and barrel

Grouping Handguns - Semi Automatic

• Semi Automatic pistols have been around since the 1890s
• Semi automatic pistols load up to 10 cartridges in a magazine clip
• Semi automatic pistols fire one bullet per trigger pull, unlike automatic weapons that fire continuously as long as the trigger remains pulled
• Semiautomatic pistols use the spent gasses from the fired round to move the parts that extract and eject the empty case
• Forward motion of the slide will chamber a new round and make it ready to fire

Semi Automatic - Glock

• The Glock debuted in the 1980s
• The Glock has 17 rounds instead of 6
• The Glock's trigger pull is ~ 5 pounds, increasing accuracy, compared to the traditional revolver, which exhibits a 12-pound trigger pull
• The Glock is light and comfortable to use as a service weapon
• The Glock is durable and functions even if it's not cleaned properly or regularly

Essential Questions for Ballistics: Day 2

• How can you distinguish among the various forms of firearms evidence, including rifling, markings on cartridges, and marks on projectiles?

Learning Targets for Ballistics: Day 2

• Ballistic evidence can be classified, including rifling patterns, breech marks, firing pin impressions, and extractor marks, based on the categories from Unit 2 (class vs individual, indirect, transfer, etc.)
• Ballistic databases are identified
• Historical forensic scientists are matched with their role in crime scene investigations

Matching a Gun to a Bullet

• It's extremely difficult to convict someone of murder without possession of the murder weapon
• Matching a bullet with a gun is essential in most cases of shooting
• Proving WHO was firing the gun requires more evidence

Ballistic Comparison Technology

• Scientists now use Ballistic Comparison technology called ATF (Automated Firearms Ballistics Technology) to digitize and automatically sort bullet and shell casing signatures
• Using the same ammunition, suspected firearms are test-fired to accurately match the breech marks and primer dent characteristics

Bullets and Casings

• Bullets or casings at a crime scene can be linked back to the weapon that was used to fire it; this relies on unique markings
• This is individualized evidence

Unique Marking #1: Rifling Pattern on Bullets

• Rifling refers to the grooves cut in a spiral down the barrel of a firearm
• Rifling increases range and accuracy
• Even though two guns may be the same model, the rifling inside the barrels will differ
• This is individualized evidence

Rifle Patterns

• Bullets can be matched to the exact gun from which they were fired, because lands and grooves scar each fired bullet with a pattern unique to that gun

Rifling Pattern

• When holding the nose of a bullet pointing away, the direction the impressions run away from you (either to your left or right) determines the direction of twist

Matching Procedure - Rifling Pattern

• Calvin Goddard pioneered forensic ballistics
• Fire bullets from a suspected weapon, then use a comparison microscope to compare these "test fires" to the questioned bullets
• Striations (lines created going through grooves and lands) must be identical for a positive match; they can be considered a "barcode" for identification

Unique Pattern #2: Breech Marks

• A breechblock prevents a cartridge from shooting backwards towards a user as it recoils
• Unique marks are produced on the casing as it moves backward and hits the breechblock
• Breech mark itself is considered class evidence

Unique Mark #3: Firing Pin Impression

• Impressions are made on the cartridge's bottom by the firing pin as it strikes to fire
• Fire pin impression itself is considered class evidence
• Firing pin impressions can appear on the rim or the center of the used cartridge, depending on the firearm and type of cartridge
• Unique marks may come from a specific gun, generating individual evidence

Unique Mark #4: Extractor/Ejector Marks

• Extractor and ejector marks are found in semiautomatic and automatic weapons
• Extractor and ejector marks form tiny scratches from the insertion and removal of the cartridge from the firing chamber

Ballistic Databases

• Firearm databases match ballistic evidence from a crime-scene to registered weapons
• Created in 1999, The National Integrated Ballistics Information Network (NIBIN) is composed of two combined databases:
• The Integrated Bullet Identification System (IBIS) contains records of ballistic markings of firearms used in previous crimes
• Drugfire is a FBI multimedia database imaging system that holds data on cartridge casings and bullets

Essential Questions for Ballistics: Day 3

• How is ballistic evidence packaged?
• How is gunshot residue processed?
• What information can investigators obtain from bullet wounds?

Learning Targets: Day 3

• Day 3 targets include explaining proper packaging of ballistic evidence, comparing/contrasting entrance and exit wounds, interpreting tests for gunshot residue, and predicting the trajectory of a bullet

Trajectory

• Trajectory refers to the path of a propelled bullet
• Ballistic evidence helps experts determine trajectory, and figure out where a shooter was located during a crime

Calculating Trajectory

• Two reference points are needed to calculate the trajectory
• Reference points can be bullet holes, gunshot residue, empty cartridges, and entry/exit points on a victim
• Pythagorean’s theorem can be used for triangulation with reference points
• To figure out where the shooter was, lasers can trace a straight-line path

Bullet Trajectory

• A bullet’s path may be slightly curved due to gravity as it propels forward, especially when shot from long distances
• Wind speed and direction may also affect trajectory

Line-of-Sight

• Sights on top of a rifle compensate for the differences between straight-line optics and curved trajectory
• Though the bullet passes through the line-of sight from below, it never rises above the line-of departure
• There is an angle due to the idea of the rising bullet
• A bullet is both rising and falling at the same time

Packaging Ballistic Evidence- Firearms

• Never submit a loaded gun to the laboratory
• Avoid excessive handling to avoid destroying latent prints
• Never pick up a weapon by placing a pencil or other object in the end of the barrel
• The serial number, make, model, and caliber of the weapon must be recorded
• Ensure weapons are placed in well packed, strong cardboard or wooden boxes to prevent shifting of guns in transit
• If blood or any other material is on the gun, place a clean paper around the gun and seal it with tape during shipment

Packaging Ballistic Evidence- Bullets and Casings

• Wrap recovered bullets and casings in paper and seal in separate labeled pill boxes or envelopes
• Bullets recovered from a body should be air dried, wrapped in paper, and not washed because doing so may destroy trace evidence
• If possible, recover unused ammunition for comparison purposes

Evidence – Clothing

• Clothing or other material showing evidence of gunpowder residue or shot holes should be wrapped carefully in clean paper and folded as little as possible
• The goal is to keep from dislodging powder particles
• Each item is packaged separately

Ballistic Evidence – Gunshot Residue

• Gunshot residue is extremely fragile evidence, and must be collected ASAP/preferably within 3 hours
• "Bag" the hand using hand protection bags when suicide is suspected or when there is valuable evidence on the hands of suspects or assault/sexual battery victims, and to prevents the loss of GSR from hands during transport to a medical examiner

Gunshot Residue

• Gunshot Residue refers to traces of smoke and unused powder particles that leave behind after the explosion of gunpowder
• GSR can land on the hand, arm, face, hair, and clothing of the shooter and victim
• Chemical tests can detect residue, even if washed
• The amount of GSR decreases as the distance between the firearm and shooter increases
• GSR patterns can be examined to determine the distance from victim to shooter

Detecting Gunshot Residue

• Primer is generally made up of barium nitrate and antimony sulfide
• GSR detection techniques focus on barium and antimony

How to Detect Gunshot Residue

• Visually and microscopically examine the evidence
• Document presence of any gunshot residues around the bullet hole as well as the shape and appearance of the hole
• Chemically process the exhibit for gunshot residues
• The first test to administer is the Modified Griess Test, because it does not interfere with later tests for lead residues
• The Modified Griess Test detects the presence of nitrite residues, a by-product of the combustion of smokeless gunpowder, and is a primary test of muzzle-to-garment distance

The Modified Griess Test Steps

• First treat desensitized photography paper with a chemical mixture of sulfanilic acid/distilled water and α-naphthol/methanol
• Evidence is placed face down against the treated photo paper, with the bullet hole centered on the paper
• Examine the back of the exhibit by steam ironing with a dilute acetic acid solution instead of water
• Acetic acid vapors penetrate the exhibit
• Acetic acid reacts with nitrite residues on the exhibit and the chemicals in the photographic paper, producing orange specks on the piece of photographic paper

Typical Patterns of Gunshot Wounds

• A gunshot within 1 inch causes a heavy concentration of smoke-like vaporous lead to surrounds the bullet hole, and clothing/skin may exhibit scorch marks from flame discharge of weapon
• A gunshot from 12-18 inches causes a halo of vaporous lead (smoke) deposit around bullet hole
• A gunshot fired from 25-36 inches causes scattered specks of unburned and partially burned powder grains to be found
• A gunshot fired from more than 3 feet will not deposit any residue on the target's surface
• The only indicator of longer distance shots is a dark ring around the bullet hole called bullet wipe

Bullet Wounds

• Eyewitness accounts are not always accurate
• Forensic evidence can confirm or dispute witness accounts
• Bullet wounds can be helpful in re-creating a scene of a crime

Determining Bullet Trajectory

• To determine bullet trajectory, figure out if a bullet came from entrance or exit of bullet
• Entrance wounds tend to be smaller because the skin stretches as a bullet enters
• Clothing fibers may embed in the wound
• Gunshot residue may be found around the wound
• If the bullet is from a close contact muzzle, there will also be burn marks caused by the gun's hot gases as they release

Entrance Wounds

• Entrance wounds can exhibit an abrasion ring and a very clear muzzle imprint in contact range gunshot wounds
• The abrasion ring forms when the force of the gases entering below the skin blow the skin surface back against the muzzle of the gun

Exit Wounds

• Exit wounds tend to be larger because the bullet carries tissue and bone that it picked up as it moved through the body
• Bullets usually do not travel smoothly through a victim, and often ricochet off bones before exiting or remaining impaled
• Fast-moving high caliber bullets tend to pass through a victim, while small caliber and low-velocity bullets tend to stay lodged in the body