Firearms, Tools, and Other Markings

bullet wipe

A dark ring around a bullet hole, left by carbon, dirt, lubricants, primer, and metal residues, usually visible when a shot is fired from more than 3 feet away.

Greiss Test

A chemical test used to detect gunpowder residues (especially nitrites) that may not be visible to the naked eye.

National Integrated Ballistics Information Network

A computerized database that stores and compares bullet and cartridge casing information to link firearms to crimes.

tool mark

Any impression, cut, gouge, or abrasion caused by a tool contacting another object.

impression

A pattern or mark left by an object pressed against a surface, such as shoe, tire, or fabric impressions.

bite mark

An impression left by human teeth on skin or objects (such as food), used in forensic investigations.

gun powder residue

Microscopic particles of burned and unburned powder expelled from a firearm when discharged.

primer residue

Trace materials (barium and antimony) from the primer cap that can deposit on a shooter’s hands when a firearm is discharged.

striation mark

Microscopic scratches left on a bullet as it travels through the rifled barrel of a firearm, unique to that weapon.

casting

A method of preserving three-dimensional impressions (like shoe or tire marks) using materials that harden into a replica.

class characteristics

Features that place evidence into a general group (e.g., size, shape, caliber of a tool or bullet).

individual characteristics

Unique features (like scratches or wear) that can link evidence to one specific source.

chemical etching

A process that uses chemicals to restore obliterated serial numbers on metal by dissolving stressed areas differently from unstressed areas.

comparison microscope

A device that allows side-by-side viewing of two specimens (like bullets or tool marks) to compare striations and patterns.

chain of custody

The documented handling of evidence to ensure it is not tampered with and can be admitted in court.

What does a star-shaped (stellate) tear pattern with a rim of smokeless lead usually indicate?

A shot fired less than 1 inch away

A halo of vaporous lead (smoke) around a bullet hole suggests:

A shot fired 12–18 inches away

Scattered powder grains without soot are typically found at what distance?

Up to 25 inches (sometimes 36)

What is the only visible indication of a shot fired from more than 3 feet away?

Bullet wipe

Which test detects invisible gunpowder residues?

Greiss test

What elements are measured to detect primer residue on hands?

Barium and antimony

Where are primer residue samples usually collected from?

Palm, thumb web, back of the hand

What does NIBIN stand for?

National Integrated Ballistics Information Network

Why can serial numbers be restored on firearms?

The metal beneath stamped numbers remains stressed

How should a firearm be safely handled at a crime scene?

By the checkered grip or trigger guard edge

What must be done before sending a firearm to the lab?

Unload it carefully

How should bullets be packaged to avoid damaging striation marks?

Wrapped in tissue paper in a pillbox or envelope