Forensic Science - Ballistics Test

Why is it important that the bullet material is softer than the barrel material?

Because then the barrel won't wear down and the gun will be good. Bullet will stay tight in barrel.

How is a comparison microscope used in ballistics lab?

Compares two bullets to see which was shot at the crime scene. Police will shoot bullet into water

Briefly describe the Beltway Sniper

John Muhammad and John Malvo killed 14 people and injured 5 people that were just doing everyday activities. All murders were done around Washington D.C. and the two shot people from the trunk of their blue Chevrolet Caprice

CSI shows have taught criminals that a filed down serial number can often be restored. What have manufacturers down to guns to allow that can't be identified even though I serial number has been thoroughly filed away?

Manufacturers has put hidden serial numbers covered with a polymer. This makes it nearly impossible for a criminal to get rid of the serial number.

Explain what happens when a gun is fired and you hear a BANG

Pulling the trigger releases the firing pin... The firing pin strikes the primer cup which holds the primer (explosive material and fuel) The primer ignites the gun powder... The powder generates large amounts of gas that propels the bullet forward through the barrel The empty cartridge case is pushed out of the firing chamber by the extractor Case is then pushed out of the gun by the ejector

Why can't a shotgun be identified the same way a rifle can?

Range from different sizes --- has a smooth barrel and doesn't have lands or grooves

How are serial numbers restored?

Serial numbers are restored by using an acidic solution the metal can be slowly eaten away.

Trajectory

The path of an unpowered object, as a missile, moving only under the influence of gravity and possibly atmospheric friction and with its surface providing no significant lift to alter the course of flight. Trajectory helps investigators to determine where the shooter was standing, etc.

Why are striations on a bullet important to a gun?

They match bullets fired from the same gun - helping in determining what gun shot a bullet at a crime scene.

Caliber

diameter of a tube or gun barrel (recorded in 100th's of an inch)

What does the gauge of a shotgun tell you?

diameter of the barrel. Gauge is determined by the number of lead balls of size equal to the approximate diameter of the bore that it takes to weigh one pound.

External Ballistics

study of the flight of the bullet from muzzle of weapon to the target. Involves specifics such as bullet shape, sectional density, atmospheric pressure and even rotation of earth

Give 4 class characteristics and 4 individual characteristics of a handgun and/or the bullets

-4 class characteristics: gage/caliber, make/model, width of lands/grooves, # of lands/grooves -4 individual characteristics: serial number, bullet striation, chamber marks, extractor/ ejector marks, firing pin, breech face marks

What are the two types of propellent and what are they made of?

-Black powder: 15% Charcoal, 10% Sulfur, 75% Potassium nitrate -Smokeless: Nitrocellulose only OR Nitrocellulose + Nitroglycerine

Bullets comparisons

-Each gun leaves distinct markings on a bullet passing through it. -A gun barrel is made from a solid bar of steel that has been drilled/hallowed out. -The drill leaves microscopic marks on the barrel's inner surface. -Gun manufacturers also add spiral grooves to the barrel. This is known as rifling. (Lands = space between grooves)

What does a cartridge contain?

-casing: has primer and propellent -capped by bullet made of lead

Describe 3 ways to collect GSR

1) GSR Adhesive Swabs 2) Swabs - 5% nitric acid on them 3) Sending entire item to lab to be inspected

Name 5 ways to test for GSR

1) Paraffin Test 2) Modified Greiss Test 3) Sodium Rhodizonah Test 4)Harrison-gilroy test 5) Neutron activation analysis test

What are three determinations a firearm expert can make when studying whether a bullet or a casing is related to a specific gun? Explain what each determination means.

1) Positive: Striations found on test bullet match striations found on crime scene bullet - This proves that it was the same gun that shot bullet at crime scene. 2) Negative: Striations do not match at all -This proves that the suspect gun did not shoot the questioned bullet found at the crime scene 3) Consistent: Some striations match but others do not - this is inconclusive

What type of info can be found out when the bullet trajectory is known?

1) Where the shooter is 2) Number of shots 3) Where the victim was standing 4)Direction gun was pointed

When and where was the first cartridge invented?

1835 in France

How is a bullet found at a crime scene packaged?

A bullet at a crime scene must be individually wrapped to prevent scratches. (Forceps shouldn't be used by doctors)

What is a choke and how are they used?

A choke reduces opening of shotgun

Why is the bore of a gun rifled? What types of guns are not rifled and how are these guns identified?

Bores are rifled because they boost the accuracy of a bullet. The rifling inside a rifle barrel makes bullets spin. Spinning helps bullets fly accurately, point first, toward the target.

Explain how to process a crime scene when a gun and other ballistic evidence is found at the scene.

Evidence should be collected

Why does so much pressure build up behind a bullet?

Explosion of gun powder --- forces bullet forward through the barrel

Where is the barrel on a gun?

FRONT OF GUN

What parts of the gun imprint markings on the casing or the bullet when the gun is fired?

Firing pin, Ejector, casing extractor, breech face mark chamber, bullet barrel striations

Why do guns "spin" and bullet?

Gently spiraled groove in barrel --- increases accuracy of bullet path

At what gun shot distance will there be no traceable GSR on the victim?

Greater than 5ft (Long distance range)

Propellent

Gun powder- Two types of propellent are Black powder and smokeless powder.

GSR

Gun shot residue Gun powder leftover from shooting a gun

What types of bullets have the greatest genetic energy?

Heavy fast bullets

Primer

Ignites the gun powder

What is the hammer of a gun for?

Strikes the barrel. The hammer is involved in firing of bullet and barrel --- leave marks on bullets after being fired.

What happens to them amount of gun powder residue on the victim as the distance a weapon is fired increases?

The amount of gun powder residue on the victim decreases as the distance a weapons in fired increases. ( So... The farther away a bullet is shot - results in less gun powder residue)

How is the study of ballistic fingerprinting said to be an inexact science?

The barrels can change over time due to rust and residue

How does a cartridge work?

When the trigger of a gun is pressed, the firing pin strikes the cartridge at a point where the primer is kept. this causes the primer to ignite. the flames produced ignited the propellent charge. The burning of the propellent charge produced large amounts of gases, which finally propels the bullet.

How is a suspected shotgun identified?

cartridge, wadding, pattern of pellet, size of pellet

Grooves

the cut or low-lying portions between the lands in a rifled bore

Lands

the raised portion between the grooves in a rifled bore

Breech-face

the rear part of a firearm barrel

Internal Ballistics

the study of the processes involved as the bullet is fired and travels down the barrel

Terminal ballistics

the study of what happens when a fired bullet strikes a target