Chapter 16: Firearms, and Tool Marks

What are types of firearm evidence?

Bullets, cartridge cases, and tool marks

No two firearms leave identical marks T or F

True, they are never identical

Q vs K comparisons are run just like finger prints and are the key to figuring out what gun/tool was used T or F

True, they are run just like fingerprints

How does the barrel work?

Guides the bullet when fired

Firing mechanism

Includes firing pin, hammer, trigger

Frame/reciever

houses the operating parts

What is the magazine/cylinder?

holds ammunition

What do forensic firearms examination primarily focus on?

pistols, revolvers, and long guns (rifles and shotguns)

Single action guns

Manually cock hammer

Double action guns

Single trigger pull

In most guns the barrel has rifling... what does that mean?

Lands and grooves inside barrel create spin

What does spin do when it comes to bullets?

Stabilizes bullet for accuracy

What creates distinctive markings on bullets?

Lands and grooves

What are some class characteristics of bullets?

number, width, and direction of twist

What are some indivdual characteristics of bullets?

Microscopic imperfections

What is the caliber of a gun?

Related to the diameter of the barrel

What are some rifle examples?

.22 and 30-0-6

What is the gauge?

describes the size of the shot gun

What is referred to as the projectile?

the bullet

What holds the componets of the gun together?

The cartridge case

What creates expanding gases?

Propellant

What initiates the firing sequence? (creates the flash)

Primer

What gives information on the cartridge base?

The head stamp

What are striations?

Parallel lines from metal-to-metal contact

What are breech face marks?

Marks from the cartridge impact

What are ejector marks caused by?

Semi-automatic weapons

What are the benefits of using a Comparison microscope?

1. Allows side-by-side comparison of evidence

2. Digital imaging enhances documentation

3. Critical when examining striations and impressions

What is the Integrated Ballistic Identification System? (IBIS)

An automated image collection system designed for firearms evidence

What does a topographic map do?

Captures 3D information

What is an important factor that markings have?

Height/depth dimension

What are the three categories of tool marks?

1. Compression

2. Sliding

3. Cutting

What causes tool marks?

When harder material contacts softer material

What are "ghost guns"?

Gun is never registered-therefore harder to trace

What is a good method to use when comparing firearms and tool marks?

Consecutive Matching Striations (CMS)

What is distance estimation?

Estimating the distance of a gun from the target surface

What is serial number restoration?

Utilizes chemical and electrochemical methods to recover all or part of a serial number stamped into a metal surface

Which of the following residues are typically detected in gunshot residue (GSR) testing?

Lead, barium, and antimony.

When a tool leaves a sliding mark on a surface (for example, a screwdriver dragged across metal), this is called a:

Striation mark

What does a match between test-fired and recovered bullets prove?

They were fired from the same firearm, to a reasonable degree of scientific certainty

The firing pin impression is located on which part of a cartridge case?

Rim or center of the primer cap

Which part of the firearm typically leaves impression marks on a cartridge case during firing?

Breech face

Which chemical technique is most commonly used to detect gunshot residue (GSR) on a suspect's hands?

Atomic Absorption Spectroscopy (AAS)

When a bullet is fired, which force primarily causes the formation of striations on its surface?

Friction between the bullet and the rifled barrel.

What is meant by the term "functionality test" when examining a firearm in a forensic lab?

A test to ensure the firearm fires safely without jamming or misfiring.

When preparing a test-fired bullet for comparison, which of the following is a recommended procedure?

Fire into a water tank or bullet recovery medium to preserve striation marks.