Forensics Chapter 15

Ballistics

the study of guns and bullets

Types of guns (general)

• handgun/pistol

• rifle

• shotgun

• machine gun

• air or bb guns

Revolver

• type of handgun

• cylinder that holds 6 bullets rotate on an axis

• reload by hand

• doesn’t eject spent shell

• shoots 1 cartridge each time the trigger is pulled

• more accurate than semi-automatic weapons

Semi-automatic guns

• eject empty cartridges

• reload automatically

• 5-19 rounds in magazine

parts of a handgun

• breech face

• firing pin

• magazine

• chamber

• barrel

• extractor/ejector

breech face

• contains the firing mechanism

• can leave unique markings on the bullet

firing pin

strikes the primer which ignites the gunpowder

magazine

holds ammunition under spring pressure to be fed into the chamber

chamber

where ammunition sits before its shot

barrel

rifled except for shotguns, where bullet travels through

• bore → diameter of the gun barrel

• lands and grooves → spiral cuts in the rifled bore

• lands are ridges of metal between grooves in rifled bore

• shotgun barrel is smooth

• guides the bullet through the barrel

extractor

hooked part of the gun that pulls the spent casing off of the bullet

ejector

pushes the cartridge case upward and out of the gun (weeee)

4 components of ammunition

1. primer (ignites propellant)

2. cartridge case

3. gunpowder (propellant)

4. bullet (projectile)

bullet terms

slug, pellet, cap, lead, ammo

cartridge case terms

casing, shell

why are bullets made of lead

cheap and malleable

What is the purpose of a bullet jacket

it is resilient and discourages disfiguration

caliber

diameter of the bullet in inches of mms (corresponds to the barrel diameter) ie. 0.45, 0.44, 0.37

how do you describe the weight of a bullet

grains (british)

cannelures

row of grooves around the cylindrical part of a bullet (holds bullet to the cartridge)

Full metal jacket

• resilient

• discourages disfiguration

jacketed soft point

• can mushroom

jacketed hollow point

• mushrooms and inflicts more pain

lead round nose

• simplest, stays intact

semi-wad cutter

target practice

wad cutter

target practice

head stamp

• shows manufacturer and size

rim fired

firing pin strikes the rim of the cartridge to ignite the primer

center fired

firing pin strikes the center of the cartridge to ignite the primer

specific things to look for in a crime scene

• missed shots with an amateur shooter

• cut out the section of material if a bullet is imbedded in it

• treat guns as if they are loaded

• separately package magazine and gun

• preserve fingerprints or other trace evidence

• unload and remove magazine (record how many bullets were present)

Firearm examiner

• analyzes bullets and cartridge cases with a microscope

• concludes as a match, no match, or inconclusive

Class evidence on a bullet

• weight

• dimensions

• type

• rifling (lands and grooves)

• cannelures

Individual evidence on a bullet

• striations

  • unique markings formed from movement, cleaning, or manufacturing of a gun

Cartridge case evidence types

• class → dimension, head stamp, rim or center fire

• individual → markings from the firing pin, extractor, ejector, magazine, chamber, breech face

Gunshot Residue Analysis (GSR)

• when gasses combust they are propelled out of the barrel of the gun and from the port (other areas besides the barrel)

• 3-5 feet

• not water soluble so the residue remains on clothes

• found on the shooter or victim if close enough

Griess Test

• detects nitrites (shows as orange specks)

• performed 1st because it isn’t invasive → on a separate sheet of paper

Sodium Rhodizonate Test

• detects lead

• bright pink

• performed directly on clothes

what kind of gun is this

handgun

what kind of gun is this

rifle

what kind of gun is this

shotgun

what kind of gun is this

machine gun

what kind of gun is this

bb gun

what type of gun is this

revolver

what type of gun is this

semi-automatic