Forensics Chapter 18 Test

Firearm

a device for accelerating a projectile to high speed towards a selected target

Cartridge

item that contains the energy that provides the driving force for the projectile

What are the 4 basic components of a cartridge?

case, powder, projectile, and primer

What are the 3 common firearms that may be involved in a crime?

rifles, shot guns, handguns

Single shot

a firearm that fires one round then requires manual ejection of the cartridge casing before another round can be fired

Semi-automatic

a firearm that fires one bullet then reloads with a new cartridge each time the trigger is pulled and released

Automatic

a firearm that continues to fire projectiles until the trigger is released

What do rifles fire? What do shotguns fire?

rifles: bullets

shotguns: small round pellets or a single projectile

What is the unit of measurement for the diameter of the barrel of a shotgun?

mm

What is the caliber of a bullet?

a measure of the diameter of the bullet

What is included on the headstamp on the cartridge?

the caliber, the manufacturer

What are the 4 events that happen when firing a bullet? (26)

1. when the trigger is pulled, the primer powder mixture ignites

2. the primer delivers a spark to the gunpowder supply

3. the pressure of the expanding gases propels the bullet from the casing and into the barrel

4. the bullet exits the barrel

Where do investigators test fire a suspected firearm to identify its individual characteristics? (50)

water-filled bullet recovery tanks

What is rifling? How does it make each gun unique?

Describe lands.

Describe grooves.

rifling: spiral grooves cut or impressed into the barrel of a gun to cause the exiting projective to spin and hence have an accurate course on leaving the barrel

lands: the raised areas

grooves: the depressed areas

What equipment do investigators use to analyze striations on bullets? (39)

comparison microscope

Indicate whether the following are CLASS or INDIVIDUAL evidence:

a. Striations on a spent bullet

b. Right or left twist on a spent bullet

c. # of Lands and Grooves

a. individual

b. class

c. class

Which is smaller—entrance or exit wounds?

entrance

Explain the database NIBIN.

National Integrated Ballistic Information: contains images of spent bullets/cartridge casings found at crime scenes

Explain the organization OSAC.

Organization of Scientific Area Committees: coordinates standards to improve the reliability of forensic science evidence including digital images of the firearm fingerprint

What do you do when a gun is recovered from an underwater location? (48)

transport it to the crime lab in a container with enough water to keep it submerged

Explain a contact gunshot wound. What does it do to the skin?

if muzzle is in contact with skin, flash burns may result

MURDER SHE WROTE:

Why was the autopsy important in solving this crime?

What types of evidence did this case analyze?

1. What role did the autopsy play in solving this crime?

- found 2 entrance and 2 exit wounds in her head (meaning that either the pistol double fired or someone shot her twice)

- Made forensic scientists investigate the case as not a suicide, but as a homicide.