Forensics Test - Firearms

Ballastics

The study of guns and bullets

Types of firearms (guns)

• Handguns/pistols (revolver and semi-automatic)

• Rifles

• Shotguns

• Machine guns

• Air or BB guns

Handgun/pistol characteristics

• Held in one hand

• Easy to carry and conceal

• Not accurate

• Limited to the number of bullets it has

• Common types: Glock, Smith & Wesson, Colt, Ruger

Revolver

• Type of handgun

• Has a cylinder that holds 6 bullets arranged to rotate around an axis to be discharged (spinny one)

• Reload by hand

• Does not eject shell

• Shoots 1 cartridge each time when shot

• More accurate than semi-automatic

Semi-automatic

• Type of handgun

• Has empty cartridge

• Reloads automatically

• Can hold 5-19 rounds (whole thing, cartridge, power, and bullet, not just bullet) in magazine/clip

Rifles

• “The long gun”

• Long barrel

• Shoots more powerful cartridges than handguns, so more accurate and greater range 

Shotguns

• “The pellets gun, used for hunting and games”

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

• Inside of barrel, not rifled

• Used for:

  • Hunting birds and other small game

  • Close quarters combat weapon and defensive weapon

  • Target shooting sports: skeet, trap, and sporting clays

Machine gun

• “Video game gun, military”

• Military weapon

• Fully automatic, keeps firing when trigger is held back

• Fires bullets in quick succession from an ammo belt or magazine

Air or BB guns

• Shot/pellets propelled by pressurized air, spring compression or carbon dioxide cartridge 

Breech face

• Part of the gun that contains the firing mechanism (right behind bullet being fired)

Firing pin

• Strikes the primer which ignites the gunpowder (also behind bullet being fired)

• Goes through breech face

Magazine

• Container that holds bullets under spring pressure to be fed into the gun’s chamber

Chamber

• Where the bullet sits before it’s shot

Barrel

• Tube part the bullets travel through before being in the air.  

• Rifled (meaning it has ridges on it that are slightly swirled longways), except for shotguns. Rifled barrel allows bullet to spin and increase its accuracy

Bore

• Diameter of a gun barrel

Lands & grooves

• Groove: Cut part of rifled barrel

• Land: Space between cut grooves

Extractor

• Hooked part that pulls the spent casing

Ejector

• Throws the spent casing from the gun

• Basically the bullet has a casing/shell on it, once it’s fired the shell comes down, there’s a hook that pulls it, the extractor, then it falls out because of the ejector)

4 Components of ammunition

• Cartridge, case/shell/casing

• Primer, first thing that ignites and starts up the gunpowder

• Propellant, the gunpowder

• Projectile, the bullet

Handgun vs. Shotgun ammunition parts

• Handgun (traditional 4 parts: cartridge, primer, propellent, projectile)

• Shotgun: Sort of same idea, has primer and gunpowder propellent. The pellets are held in a tray (called a plastic body, that whole thing gets shot out too?)

What are bullets made out of

• Lead, sometimes jacketed with brass, copper or steel

Why is lead a good material for bullets?

• Extremely dense (good for inertia)

• Soft metal (able to mold and mushroom)

• Cheap

• Can be jacketed which prevents disfiguration and makes it more resilient

Caliber

• Diameter of a bullet

• Can be inches or metric

• Must correspond to the diameter of the barrel (cos it needs to go through duh)

What is the unit for bullets?

Weight, expressed as grains (British unit)

Cannelures

• Groove around the cylindrical part of the bullet

• The 2 ridges, allows the cartilage case to grip onto the bullet 

• Holds it intact until the gun powder can travel

Types of bullets & their properties

• Full metal jackets

• Jacketed soft point

• Jacketed hollow point 

• Lead round nose

• Semi-wad cutter

• Wad cutter

Full metal jacket

• Resilient, discorouages disfiguration, viewed easily

Jacketed soft point

• Can mushroom (disfigure and flatten out)

Jacketed hollow point

• Mushrooms, causes more pain

Lead round nose

• Simplest, stays intact

Semi-wad cutter + wad cutter

• Target practice

Head stamp

• On bottom of bullet

• Contains manufacture and size 

• The firing pin can contact the head stamp either around the rim or in the center

Steps for collecting evidence

1. Number the evidence

2. Photograph evidence

3. Document & take notes

4. Use gloves to collect evidence

5. Separate sealed envelope for each piece

Types of ballistics evidence that can be collected

• Bullets:

  • Look for missed shots

  • If embedded into an area, cut out section of area with the bullet in it, don’t just take out the bullet

• Cartridge cases

• Gun:

  • Always treat like it like it’s activated

  • Unload and remove magazine (record how many bullets were in the magazine)

  • Separately package magazine and gun (in a special box)

  • Take care of preserve fingerprints or other evidence

• Gunshot residue

• Measurements and angles

• photo and video surveillance

What to examine at the lab with ballistics

• Examine to determine

  • how many shots were fired?  

  • what kind/type of gun - database 

  • if all were shot from same gun? - compare using microscope to find a match

Ways to examine and determine bullet

• Think of the activity in class

• Weight

• Dimensions

• Types (full metal jacket, wad cutter, etc.)

• Rifling (lands and grooves)

• Cannelures (small ridges around top part of bullets, wraps around)

Striation

 Individual evidence produced by movement in the gun, cleaning or manufacturing

Cartridge case examination & determination

• Head stamp, dimensions, rim or center fire (CLASS)

• Unique impressions. Ex. firing pin, magazine, extractor. All parts. of the bullet are unique evidence (INDIVIDUAL)

Gunshot residue

• Happens when gasses combust:

  • Propel bullet

  • Blow out from ejector port + barrel 

• Travels 3-5 feet

• As the firearm gets closer, the residue concentrations increase

• Elements contained in gunshot residue are not water soluble so the residue can stay on clothing

  • You can burn the clothes to get rid of it

• Can be found on shoot, victim if close enough, or bullet hole if close enough

2 Types of tests to analyze gunshot residue

• Griess test

• Sodium Rhodizonate

Griess test

• Performed first, does not interfere with other tests

• Detects nitrites (product of combustion)

• Results are orange specks

Sodium Rhodizonate

• Detects lead 

• Results are bright pink