Forensics Unit 7: Ballisitics

Handgun

a firearm designed to be held, aimed, and fired with one hand (revolvers and semi-automatic pistols)

• short barrel length

• shoots cartridges

• measured in caliber

Rifile

a shoulder-fired firearm, characterized by helical grooves for high accuracy over long distances

• used for hunting, warfare, and sport, commonly designed to be held with both hands

• long barrel

• shoots cartridges

• measured in calibers

Shotgun

a long-barreled, usually smoothbore firearm designed to be fired from the shoulder

• used for hunting, sport, and home defense

• short barrel

• shoots shotshells

• measured in gauge

What is rifiling in a gun barrel?

cutting or forming helical (spiral) grooves into the internal surface of a gun barrel to impart a spin on a projectile

What is the purpose of rifling?

mpart a rapid spin on a projectile (missile)

Which guns have rifling in their barrels?

handgun and rifle

the higher the caliber…

the larger the gun

the higher the gauge…

the smaller the gun

caliber

the diameter of a bullet or firearm barrel, usually measured in hundredths/thousandths of an inch

gauge

the inner diameter of its barrel (bore), primarily used for shotguns

How is a cartridge fired?

• the firing pin wack the primer on the cartridge, causing a spark that ignites the gunpowder

• the explosion pushes the bullet out of the casing and out of the barrel of the gun

• pushes the cartridge case in the other direction, slams it into the breech face

• casing is extracted from the gun

How is a shotshell fired?

• firing pin wack the primer, causes a spark, ignites gunpowder

• explosion pushes wad and pellets out of casing and down the barrel

• pellets spread out

• pushes shell case in other direction and into the breech face

• casing is ejected from the gun

When collecting firearm evidence, why is it important not to put anything into the gun barrel or touch the breech face of the gun?

• can add additional marks to the gun

• preserves evidence (DNA, fingerprints)

When a gun is found in water, how do you submit it to be analyzed?

• keep it in the same water and in a sealed container

How to make sure two bullets are not touching when packing them together?

cover them in fabric or cotton

How is clothing packaged?

in paper bags or boxes

Why is important to dry out any wet/bloody clothing before it is packaged?

mildew can destroy evidence/makes anylzing difficult

What does the firearms division also examine?

• tool marks

• explosives

characteristics of bullets and casings

• brand/manufacturer of the ammunition

• bullet weight shape/size

• material used in the bullet (brass, copper, steel)

• headstamp (text found around the primer)

• caliber/gauge of the ammuination

What is the tank that test fires a suspect’s gun?

ballistics water tank or a bullet recovery water tank

• The tank uses the friction and density of water to decelerate and stop a bullet without damaging its surface. This preserves the unique microscopic markings, or striations, left by the barrel of the gun

What tool allows CSI to see two bullets/cartridge cases at the same time?

comparsion microscope

What do analysts do when they need to test fire a damaged/broken gun?

replace broken parts with components from a large, in-house inventory of donor firearms to restore functionality

How do anylsts figure out how far a victim was from a shooter?

examining the density and spread of gunshot residue (GSR)—specifically soot and stippling—on the victim's clothing or skin

• Measure the gun from a piece of fabric/clothing from different distances

How can they identify a crimes scene that has no gun?

state database

• IBIS

Who invented the comparion microscope?

• Phillip Gravelle

• Calvin Goddard

firing pin

firearm components that strike the primer on a cartridge to initiate firing

What part of the cartridge does the firing pin strike?

primer

How is a breech mark made?

the area surrounding the firing pin

• bullet comes out of the barrel and cartridge case case also comes out the other direction, slams against back part of the gun

types of breech face marks:

parallel, mattled, circular

extractor

grips the time of the cartridge case marking bothe the case head and side of the rim

location of extractor mark on the casing

the rim of the cartridge case

ejector

what the case is pulled back against pushes the case

location of an ejector mark on the casing

within or on the edge of the extractor groove, typically at the base of the cartridge casing

How are rifling striations made?

etched into the bullet by the riflin lands

• grooves inside the gun

Is rifling direction class or individual evidence?

class

IBIS

Integrated Ballistic Identification System

• associates evidence in previously solved crimes

Gunshot residue

residue expelled from a firearm after shooting

• brunt/unbrunt particles from the explosive primer, gunpowder, etc

What is the problem is GSR tests?

high contamination risks, rapid loss of evidence, and lack of definitive proof