FIS 201 Exam 3 Set 3: Lectures 20–21 — Firearms and Ammunition

What does a firearms examiner investigate?

Firearms, bullets, cartridge cases, gunshot residue, and related evidence to answer questions about firearm use and possible sources.

What is the action of a firearm?

The mechanism responsible for loading, firing, and, depending on the design, extracting or ejecting ammunition.

What is the barrel of a firearm?

The tube through which a projectile travels.

What is the stock or grip of a firearm?

The part held by the shooter to control the firearm.

What is the chamber of a firearm?

The area that houses a cartridge during firing.

What is the breech?

The rear area of the chamber.

What is the firing pin?

The component that strikes the primer to initiate ignition.

What is the trigger?

The mechanism operated to initiate firing.

What does an extractor do?

It pulls or removes the fired cartridge case from the chamber.

What does an ejector do?

It helps expel a cartridge case from the firearm.

What is a magazine?

A component that holds and feeds ammunition in compatible firearms.

What is a cylinder?

A rotating component that holds cartridges in a revolver.

What is a rifled barrel?

A barrel with spiral lands and grooves that impart spin and leave characteristic marks on bullets.

What is a smoothbore barrel?

A barrel with a generally smooth interior, commonly found in shotguns.

What are lands in a firearm barrel?

The raised portions inside a rifled barrel.

What are grooves in a firearm barrel?

The recessed portions between the lands of a rifled barrel.

What is caliber?

A measurement or designation generally associated with bullet or firearm bore diameter.

What is gauge?

A traditional shotgun classification based on the number of spherical lead balls of bore diameter that would weigh one pound.

How does shotgun gauge relate to bore size?

For conventional gauges, a smaller gauge number generally indicates a larger bore.

What are the four main components of a metallic cartridge?

Case, primer, propellant, and projectile.

What is the function of a cartridge case?

It holds the cartridge components together.

What is the function of a primer?

It initiates ignition when struck.

What is the function of propellant?

It produces expanding gases that propel the projectile.

What is the projectile?

The object propelled out of the firearm, such as a bullet.

What is a typical shotgun shell made of?

Shot or a single projectile, wad, propellant, primer, and case or hull.

What is gunshot residue (GSR)?

Residue associated with firearm discharge that may include material from the primer, propellant, projectile, case, and firearm.

What does the Griess test detect?

Nitrite compounds associated with burned or partially burned propellant residues.

What does sodium rhodizonate detect?

Lead.

What does SEM-EDX stand for?

Scanning Electron Microscopy with Energy-Dispersive X-ray Spectrometry.

What is SEM-EDX used for in GSR analysis?

Examining microscopic particles and analyzing their elemental composition.

Which elements may be associated with traditional primer residue?

Lead, barium, and antimony.

What is serial number restoration?

A forensic process that may reveal stamped markings after their visible characters have been removed.

Why can a removed firearm serial number sometimes be restored?

Stamping can create a zone of metal deformation beneath the visible characters.

What is trigger-pull measurement?

Measuring the force required to operate a firearm's trigger.

What is a hair trigger?

A trigger that requires relatively little force to operate.

Does a light trigger pull alone prove an accidental discharge?

No. The firearm's condition and other evidence must be evaluated.

What is the difference between a rifle and a shotgun?

A rifle typically has a rifled barrel and fires bullets; a conventional shotgun typically has a smoothbore barrel and fires shotshells.

What is the difference between a pistol and a revolver?

A pistol commonly uses a slide or bolt and a magazine, while a revolver uses a rotating cylinder.

What is a cartridge case headstamp?

Markings on the base of a cartridge case that may indicate the manufacturer and cartridge designation.

What is a class characteristic of a bullet?

A feature shared by a group of bullets or firearms, such as caliber or rifling characteristics.

What is an individual characteristic in firearm identification?

A microscopic detail that may help distinguish one firearm from another.

What marks can a rifled barrel leave on a bullet?

Rifling impressions and microscopic striations.

What is a breechface mark?

A mark produced when the cartridge case contacts the breechface during firing.

What is a firing-pin impression?

A mark left when the firing pin strikes the primer.

What are extractor marks?

Marks that may be produced when the extractor grips or pulls a cartridge case.

What are ejector marks?

Marks that may be produced when the ejector expels a cartridge case.

What is an exemplar in firearms examination?

A known bullet or cartridge case produced using a firearm for comparison with questioned evidence.

Who was Calvin Goddard?

A physician and U.S. Army officer who helped advance forensic firearms identification and comparison microscopy.

What is a comparison microscope used for in firearms examination?

Comparing microscopic marks on questioned bullets or cartridge cases with known exemplars.

What is a headstamp useful for?

Helping determine ammunition manufacturer and cartridge designation.

What does NIBIN stand for?

National Integrated Ballistic Information Network.

What does IBIS stand for?

Integrated Ballistic Identification System.

What is NIBIN used for?

Supporting investigations by identifying potential associations between ballistic evidence, particularly cartridge cases.

What is the difference between AFIS and NIBIN?

AFIS searches fingerprint databases; NIBIN supports ballistic evidence comparisons.

Does a NIBIN association automatically prove that a particular firearm fired a cartridge case?

No. It provides an investigative lead that requires further examination.

What are the three common conclusions in forensic comparison?

Identification, exclusion, and inconclusive.

What does an identification conclusion mean?

The observed characteristics support the conclusion that the evidence came from the same source.

What does an exclusion conclusion mean?

The observed characteristics rule out a common source.

What does an inconclusive conclusion mean?

The evidence is insufficient for a confident identification or exclusion.