Forensics Ballistics Test

actually cooked wth

Types of firearms

handguns/pistols (semi-automatic or revolver), rifles, shotguns, air or bb guns

Features of handguns/pistols (5)

• held in one hand

• easy to carry and conceal

• not accurate

• best at 5-9 feet

• limited # of bullets

Revolver

• Reload by hand

• cylinder holds 6 bullets

• doesn’t eject spent shell

semi-automatic

• shoots 1 cartridge each time trigger is pulled

• empty cartridges

• reloads automatically

• holds 5-19 rounds in magazine clips

rifles

• long barrels

• has a butt stock which steadies the weapon and absorbs recoil

• better accuracy and greater ranges bc they have sight on them (shoots more powerful cartridges than hand guns)

• fully automatic —keeps firing when trigger is held back

shotguns

• inside of the barrel is not rifled (no markings)

• similar to rifles, but shoots a packet of spherical pellets

airguns and bb guns

pellets or shots are propelled by pressurized air, spring compression, or co2

• doesn’t hold actual ammunition

parts of a revolver (8)

• grip

• trigger

• trigger guard

• hammer

• cylinder

• muzzle

• ejector rod

• sight

hammer

part that strikes the primer to cause ignition

grip

handle of the handgun— usually plastic

ejector rod

metal rod used to help w/ removal of cartridges

cylinder

storage for ammunition in revolver — rotaes when action is cocked

muzzle

end of gun

trigger guard

prevents gun from going off

sight

part that helps line up stuff you want to shoot

parts of a handgun

trigger guard, muzzle, trigger, hammer. barrel (like a pez dispenser)

• slide: moves back to load cartridges

• safety lock: prevents bullets from moving up

• magazine: holds 5-19 bullets, goes up from grip

what type of guns do police often carry?

semi-automatic pistols

breech

portion of the gun that contains firing mechanism

breech face

face at the back of the gun that touches the back of the bullet case or cartridge

breech marks

imparted to central area of casings at the primer when cartridge is slammed backwards

• caused by breech faces

• has unique marking

• ammunition can be used to match up to the type of gun

breech marks class evidence

type of breech face used by manufacturer

breech marks individual evidence

specific markings on the breech face due to wear

firing pin

moved by hammer; strikes the primer to ignite gunpowder

• leaves unique impression on cartridge casing

magazine

container that holds ammunition under spring pressure to be fed into the chamber

• individual bc of how gun handles and fires the bullet — changes over time

chamber

where ammunition sits b4 shot

barrel

• rifled for every besides shotgun

• puts a spin on bullet to make it accurate

• bore

bore

diameter of a gun barrel

ammunition (4)

• cartridge case

• primer

  • lead styphnate, barium nitrate, and antimony

• propellant; smokeless nitrocellulose powder

• projectile — bullet

bullet material

made of lead and jacketed with brass, copper, or steel

caliber

the diameter of a bore of a firearm; measured in mm or in

• bullet size

• .22 caliber = 22/100 of an inch

• 9mm ~ .38 cal.

gauge

the interior diameter of a shotgun barrel; determined by # of lead balls that fit into the barrel that = one pound

full metal jacket

entire casing covered in copper or steel

• has a lot of force & better accuracy

• can pass through target if they don’t hit something significant like the bone

jacketed soft pont

top part is rounded with lead, bottom is encased in copper

jacketed hollow point

lead tip in has hole, and does a lot of damage inside of the body bc of the way it enters

• regulated for buying

non-jacketed bullets

lead round nose, semi-wad cutter, and wad cutter

• wad cutters are found in rifles

hollow point bullets

aka cop killers

• created to maximize bullet efficiency

• “mushrooms” and strikes at a high velocity

• it expands and slows down, doing more damage

• penetrates through multiple obj like glass, clothing, etc

class evidence in bullets

WDSTR

• weight

• dimensions

• shape

• type

• rifling

rifling

bore of a gun that is machined to form a grooved spiral

individual evidence (bullets)

striae & cannelures

• striae — unique markings and wear

striae

parallel sets of scratches on a bullet caused by markings on the bore

• microscope is necessary to see marks

• can be matched to a weapon or bullet from other crime scenes

cannelures

fastens bullet to cartridge case

• creates marks on bullets when it separates from casing

class evidence for cartridge

• dimension of shell casing

• head stamp

• rim

• centerfire

head stamp

numerals, letters, symbols, on base of cartridge showing manufacture, caliber, and code

rim

primer on circumference base

centerfire

primer in center of base

individual evidence for cartridge

• firing pins

• breech marks

• chamber

• extractor

• ejector

• magazine

chamber (individ evidence for cartridge)

marks on chamber caused by movement across chamber when loading and removing

extractor

hooked or crescent shaped part attach to breech block which withdraws spent casings from chamber when the breechblock separates from barrel after firing

ejector

part of the gun whose function is to throw out spent casing after firing

class evidence of firearms

• bullet type

• caliber

• weight

• lands & grooves

• rifling

• cartridge case

• head stamp

individual evidence of firearms

• striae

• firing pin marks

• breech marks

• extractor marks

• ejector marks

• chamber marks

determine distance of bullets (2)

GSR analysis and trigonometry

• both have error rates and not absolute, so use multiple methods

bullet holes in clothes

bullet holes will have smaller diameter than the actual bullet bc of fabric elasticity

higher the velocity =

the greater the damage

bullet wipe residue

traces of lead leave a ring of residue

what happens when gases combust

1. propels the bullet and blows it out from the ejector port and barrel

GSR contains what materials

ejector particles, combustion residue, and unburned powder particles

how far does gsr residue travel?

3-5 ft from the barrel

what happens to residue if the firearm gets closer

the residue concentration around the bullet hole increases

elements in gsr are…

are not water soluble —residue remains on clothing after washing

where is gsr found

• shooter

• victim (if close enough)

• around bullet hole (if close enough)

methods to test for gsr (3)

1. visual/microscopic examination

2. griess test

3. sodium rhodizonate test

what is gsr analysis used for?

• determining gun to wound distance

• uses same firearm to make test samples

• minimum distance (gun could be no closer than…)

• maximum distance (gun could not be further than…)

griess test

• performed 1st so it doesn’t interfere w/ other tests

• detects nitrites (product of combustion)

• results in orange specks

• closer the gun, more concentrated

sodium rhodozionate test

• detects if lead residues are present

• reacts w/ lead and becomes very bright pink

• closer the gun, more concentrated the gsr

how are gun shot wounds determined?

the wound shape, characteristics, and presence of gsr, etc

gunshot wounds classifications

contact, intermediate range, distant range

contact

gun is placed directly next to body or within a few inches

intermediate range

gun within 2-3 feet of target

distant range

gun is more than a few feet away

contact wounds (4)

• barrel is in contact w/ skin

• star shaped laceration due to gases released

• no gsr on skin bc INSIDE THE BODY

• can cause abrasion ring in the shape of muzzle

intermediate wounds (2)

• powder tattooing of blood

• entrance site is irregular bc bullets can tumble

distance wound

• wound shows no powder marks bc gun is far away

• clothes on victim may have powder on them— not visible but can be detected using tests

• wounds have clean edges

angle of impact

arcsin (minor axis/major axis)