Forensic Science: Firearm Ballistics Quiz

Firearms and Toolmarks

• Firearms identification is a branch of forensic science.
• It focuses on the microscopic comparison of imperfections left by specific firearms on fired bullets and cartridge cases.
• The uniqueness of each firearm is transferred to the cartridge case and bullet when fired.
• This uniqueness is proven by physics, metallurgy, metallography, and materials science.
• Variations in structure (scratches, nicks, breaks, and wear) allow analysts to link a bullet to a specific gun.
• This can also be used to link a scratch or abrasion mark to a tool.
• Similarly, cartridge cases from multiple crime scenes can be linked.

Ballistics vs. Firearms Identification

• Ballistics is the study of projectiles in motion, a branch of applied physics.
• Ballistics considers factors like humidity, temperature, wind, projectile weight, projectile velocity, curvature of the earth, and distance traveled.
• Firearms identification compares microscopic imperfections on fired bullets and cartridge cases.

Introduction

• Firearm and toolmark examination individualizes physical evidence to a source.
• Structural variations and irregularities (caused by scratches, nicks, breaks, and wear) are used to determine relationships between items, such as between a bullet and a gun.

Revolver Parts

• The image shows the different parts of a revolver, with labels.

Pistol Parts

• The image shows the different parts of a pistol, with labels.

Rifle Parts

• Parts of a bolt-action rifle
• The rifle has similar but also different parts from revolvers and pistols.
• The bolt: a moving metal block
• The bolt handle: used to open a bolt action.
• The safety: a device to prevent accidental firing
• The stock: handle of the firearm.
• The chamber: used to hold the cartridge, for shooting.
• The barrel: Metal tube through which the projectile travels
• The forestock: helps support the firearm
• The magazine: a container for ammunition, that helps load into the chamber
• The trigger: small lever to initiate the firing process
• The breech: rear end of the barrel where a pin strikes the cartridge
• The receiver: Metal housing for all acting parts
• The butt: the part of the stock you hold.
• The muzzle: the end of the barrel, where the projectile exits
• Other firearm parts including the bore, breech, firing pin, and receiver.

Shotgun Parts

• The image shows the different parts of a shotgun, with labels. (safety, action bar, sight, stock, trigger, forestock - or fore end, etc.)

How a Gun Works

• The cycle of fire: feeding, chambering, locking, firing, unlocking, extraction (pulling), ejection (pushing), and cock.

Firing a Weapon

• Trigger pull releases the firing pin to strike the primer.
• This then ignites the powder; expanding gases propel the bullet.
• Simultaneously, the spent cartridge case is propelled backward.
• The cartridge case is marked by its interaction with the metal surfaces during firing and loading.

General Rifling Characteristics

• Essential characteristics associated with firearms' rifling include caliber, grooved impressions, conventional vs. polygonal rifling, number of lands and grooves, land and groove widths, and rifling groove twist direction.

Gun Barrel Markings

• Gun barrels are made by drilling from a solid steel bar.
• Microscopic drill marks left on the barrel's interior are random and irregular, giving each one a unique pattern.
• Surfaces between grooves are called lands.
• Grooves guide the bullet and impart a spin for accuracy.

Gun Barrel Markings

• The surfaces between the grooves are called lands.
• Grooves help direct the fired bullet and impart spin, improving accuracy.

Gun Barrel Markings

• Unique inner surface striations created during manufacturing.
• These striations are particular to each barrel and form the unique marking characteristics.

Shotguns

• Unlike rifled firearms, a shotgun has a smooth barrel.
• Shotguns generally fire small lead balls or pellets that don't have the striations of rifled barrels.
• Shotgun diameter is measured by gauge, higher gauge numbers indicate smaller diameters.

Caliber

• Caliber is the diameter of a rifle or handgun barrel measured between opposite lands.
• Standard calibers are usually expressed in hundredths of an inch.
• Metric calibers are often combined with the bullet diameter and cartridge length.

Ammunition

• Cartridges consist of four components: case, primer, powder, and projectiles (bullets, slugs, or shot).

The Fired Bullet

• The lands and grooves of the barrel imprint themselves on the fired bullet.
• Examiners identify class characteristics (caliber, number of lands and grooves, widths, and twist direction) to narrow possible sources.

Firearms Analysis

• Bullet, cartridge case, and shotshell comparisons are conducted.
• Weapon operability, comparison of action marks, bullet trajectory determinations, serial number restoration, distance & shot pattern, and toolmarks are assessed.
• Other analyses, such as trigger pull determinations, safety function, and ammunition capacity, may be done.

Conducting the Exam - Step #1

• A thorough exam of the firearm is done, with notes taken on its functionality, trigger pull, markings, and features.
• A variety of data points are collected and recorded.

Conducting the Exam - Step #2

• The weapon is test-fired into a water tank, and bullets and cartridge cases are collected.

Conducting the Exam - Step #3

• The recovered cases and bullets are compared using a comparison microscope.

Comparison Microscope

• Examination permits simultaneous observation of two bullets, enabling the comparison of width and longitudinal striation on each.
• Identical markings suggest a likely source.

Bullet Examination

• No two rifled barrels have identical striation markings.
• Bullet caliber, land and groove number and direction of twist differentiate the origin of fired bullets.

Cartridge Cases

• Cartridge cases show markings from the breechface, firing pin, ejector marks, and chamber striations.

Marks on Cartridge Cases

• The firing pin, breechblock, ejector, and extractor impart unique characteristics to cartridge cases.
• Comparison of marks (breech face, firing pin hole) helps determine whether a firearm from a test fire matches one from a crime scene.

Cartridge Case Comparison

• Firing pin, breechblock, ejector, and extractor mechanisms leave striations on cartridge cases, providing unique identification characteristics.

Firing Pin Impressions

• Firing pin marks are visible on primer portion of cartridge case.
• These impressions are a critical aspect of examining similarities.

Cartridge Case Comparison

• Ejector and extractor markings assist in linking cartridges to specific firearms.
• The unique markings on the case are used to ascertain the identity of possible sources for cartridge cases.

Extractor

• The extractor is a part of the firearm that helps eject the cartridges from the weapon.
• The use of extractors helps in determining uniqueness between cartridge cases.

Ejector

• The ejector is a firearm part that ejects cartridge cases, creating distinct marks on the rim.

"The Kaufman DA Murders"

• Describes events in the murders of Mark Hasse and Mike and Cynthia McLelland, along with suspect Eric Williams.

Suspect - Eric Williams

• Eric Williams was a Justice of the Peace in Kaufman, TX.
• He had a history as a former police officer and member of Mensa.
• He was convicted of stealing computer monitors.
• He owned many firearms and cartridges.

The Evidence

• Bullets and cartridges recovered at the scene linked the crimes to a suspected firearm.
• Some recovered firearms were connected to the crimes with matching serial numbers or other identifiers.
• This evidence contributed to linking specific guns to the murders.

Evidence (cont.)

• Cartridge cases and the two recovered revolvers from the Crime Scene are linked to the guns from the storage unit.
• An identified revolver is linked to bullets from Hasse's autopsy.

Emerging Technologies

• Modern methods use aspects of imaging and computer-based comparisons (such as confocal microscopy, gel-sight, and laser scanning).
• Algorithms and systems like NIST's Congruent Matching cells and the IBIS/NIBIN systems also are used.

Confocal Microscopy

• Uses a laser as a light source.
• Images along multiple focal planes.
• Images are independent of surface irregularities and reflectivity.

Imaging Algorithms

• Computers excel at detecting subtle variations in gun components.
• NIST's congruent matching cells algorithm is used for improved identification.
• Computers differentiate more shades of grey than humans— aiding in analysis.

NIBIN Network

• A database of bullets and cartridge casings from crime scenes and test fires.
• Links a specific weapon to a crime.

Firearms Evidence Collection

• Firearm evidence collection methods involve holding the weapon by the trigger guard or grip.
• Necessary precautions avoid accidental discharge.
• Revolver chambers, their position, and corresponding cartridges are documented.

Firearms Evidence Collection (cont.)

• Bullets are scribed with investigator initials.
• Obliterations of striation markings must be avoided on bullets.
• Fired cartridges are identified with investigator initials— near the mouth of the shell.
• Discharged shotgun shells are initialed on the metal.

Gunshot Powder Residue

• Unburned and partially burned gunpowder particles are propelled outward from the barrel and toward the target.
• The pattern created when a shot is fired can indicate the distance from which a shot was fired.
• Gunshot residue is used for these distance estimations.

Gunshot Powder Residue (cont.)

• Gunshot residue patterns are assessed for distance estimations using microscopic and chemical tests.
• The estimations are affected by variables (handling, intervening objects, etc.).

Distance Determination

• Comparing test patterns to patterns from victims' clothing/skin determines the distance of the shooting, based on residue patterns.

Distance Determination (cont.)

• A stellate tear pattern around a bullet hole from a weapon fired in short range (e.g., <1 inch) often occurs.
• A halo of vaporous lead (smoke) deposited around a bullet hole usually occurs in weapons fired between 12-18 inches.

Distance Determination (cont.)

• The presence of scattered powder grains and/or the absence of larger debris along with traces of smoke is used.
• Test and evidence patterns analysis enables a reasonably accurate estimation of the distance from where the shot was fired.

Distance Determination (cont.)

• The firearm evidence is examined microscopically to detect gunpowder residue.
• Chemical tests identify the gunpowder residue that is not visible.
• The process may involve samples taken at various distances to determine the pattern.

Distance Determination (cont.)

• Shotgun firing distances can be compared with test fires.
• Establishing muzzle-to-target distances is made by assessing the spread of shot pattern (discharged shot).

Primer Residue on Hands

• Gunpowder and primer residue is blown back towards the shooter.
• This residue is often found on the firing hand, assisting in determining if recent weapon discharge occurred.

Primer Residue on Hands (cont.)

• Examiners measure the levels of lead, barium, and antimony on relevant areas of the suspect's hands.

Primer Residue on Hands (cont.)

• Morphology of particles determines whether a person recently fired a weapon or was near a discharged firearm.

Serial Number Restoration

• Forensic scientists may be asked to restore serial numbers lost through grinding, rifling, or punching.
• Chemical etching may reveal obliterated serial numbers due to the deformation zone's faster chemical reaction.

Serial Number Restoration (cont.)

• Stamped serial areas differ chemically, physically, and magnetically from the surrounding metal.
• These differences aid in restoration, and the physical properties of metal (reaction to chemicals, heat, and magnetic fields) are used.

Visualization After Chemical Etching

• Different metal reaction and visibility to chemical etching shows the strained metal grain boundaries from unstrained metal areas.
• This enables visualization of obliterated serial numbers.

Toolmarks

• A toolmark is any impression, cut, gouge, or abrasion made when a tool contacts another object.
• Examinations reveal class characteristics (size and shape of tool), and minute imperfections for a unique identification.
• These characteristics aid in determining if similar-looking tool marks.

Toolmarks (cont.)

• Typical tool types include shearing (offset jaws), pinching, slicing, prying, and gripping tools.
• The presence of any unique tool marks on a tool is crucial information for individual identification of the tool.

Toolmark Evidence

• The entire tool that has the toolmark or the part of the object with the tool mark must be submitted to the crime lab.
• The crime scene investigator should never fit the suspect tool in the tool mark, which may alter evidence and raise concerns about its integrity.

Evidence Submitted to the Lab

• Visual aids such as pictures of items from the crime scene illustrate and enhance the identification process.

Toolmark Analysis

• Tests are performed to validate how tools such as bolt cutters and pry bars affect objects such as locks.
• These tests help determine if marks on an object were made by a suspect tool.

Toolmark Analysis (cont.)

• Silicone rubber casts from crime scene object tools are compared to test casts of known specimens.
• This analysis helps connect the tool marks to a specific tool of interest.

Test your knowledge on the critical aspects of ballistics within forensic science. This quiz covers the identification of firearms, the function of rifling, and the cycle of fire, among other key topics. Perfect for students and professionals interested in forensic ballistics.