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Ballistics By the end of this unit you will be able to:

o Explain the differences between a handgun, a rifle, and a shotgun

o Know the series of events in the gun which cause the bullet to leave the barrel.

o Describe unique markings that may be used to identify bullets or guns used in cases.• Lands and grooves

• Rifling

• Firing pin impressions

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Ballistics

o Describe how bullets are test fired and matched in the laboratory

o Discuss the role of ballistics recovery and examination at a crime scene

o Determine the position of the shooter based on bullet trajectory

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Introduction Introduction

Ballistic evidence helps explain: o What type of firearm was used o The caliber of the bullet o The number of bullets fired o Where the shooter was locatedo Whether a weapon was fired recently o If a firearm was used in previous crimes

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ReviewReviewFirearms and Rifling Firearms and Rifling

o Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracy

o This leaves a pattern on the bullet that is unique

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Review:Review:Bullets, Cartridges, and Calibers Bullets, Cartridges, and Calibers

o Cartridge—a case that holds a bullet, primer powder, and gunpowder

o The bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind.

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Review:Review:How a Firearm Works How a Firearm Works

2. The primer powder sparks through the flash hole to the main propellant supply

1. The firing pin hits the base of the cartridge, igniting the primer powder

3. The pressure of the explosion pushes the bullet from the casing into the barrel

4. The bullet follows the lands and grooves spiraling out of the barrel

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Caliber of the Cartridge Caliber of the Cartridge

o Caliber—a measure of the diameter of the cartridge

o In hundredths of an incho Common calibers include

.22, .25, .357, .38, .44, and .45o Why should the caliber of ammunition

match the firearm that shoots it? • If they do not match, what could go wrong?

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Review:Review:The Study of BulletsThe Study of Bullets and Cartridge Casings and Cartridge Casings

1. How is each fired bullet marked?

2. What is the procedure to match a spent bullet to the firearm that shot it?

3. What makes up a test-firing, and why is it done?

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Review:Review:Marks on the Marks on the Spent Cartridge Casings Spent Cartridge Casings

– Evidence found at a crime scene

o Firing pin marks • appear on the rim or center of the spent cartridge• can be used to match a cartridge to a firearm

IBIS Integrated Ballistic Identification System

o Program controlled by the ATF (Bureau of Alcohol, Tobacco, & Firearms)

o Software and program which produces a digital history of bullets,casing,and cartridges.

o FBI and ATF joined forces and use a super powered computer now to track ballistic evidence left at crime scenes

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Gunshot Residues Gunshot Residues

o Gunshot Residues (GSR)• Particles of unburned powder and traces of smoke • Leave traces on the hand, arm, face, hair, or clothing

of the shooter and/or victim • Hot gasses may cause burns

o Chemical testing can detect residue even if removal is attempted

o 3 elements :lead, antimony, & barium; all 3 must be present to be used in court

How a spectrophotometer works

o Spectrophotometer is the name of a machine which can identify elements and the amounts of each element to create a spectrum chart.

o http://youtu.be/pxC6F7bK8CU

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Height of peak shows

concentration

Location on X-axis ID’s type

of element

Distance Identification

o Distance from victim to shooter can be determined by examining the residue pattern on the victim• If muzzle touches victim: burns, powder and partial

bullet fragments will be imbedded into wound. Blood and tissue back backsplash onto gun or shooter.

• At a distance, less powder and burning occurs to victim.

• Powder will coat clothing and hands of shooter but can be washed off. This is why crime scene investigator tape brown bags over the hands.13

Wound Patterns

o Entry wounds• Smaller than exit wounds• Entry wounds can pull fibers into body• If close contact= star shaped or shredded

appearance• Distance very neat entry wound• Can be difficult if bullet ricochets off bone• Caliber and velocity affect wound appearance

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Trajectory Trajectory

o Two reference points are needed to define the trajectory

o Investigators canfigure the shooter discharged the firearm somewhere along that line

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Trajectory Trajectory

o Reference points can be • bullet holes in objects or victims• An entry point and exit point on a victim • Gunshot residue or spent cartridge casings

o Lasers can trace a straight-line path to determine the position of the shooter

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Trajectory and Gravity Trajectory and Gravity

o Bullet’s path is slightly curved

o Gravity pulls it downward as the bullet moves forward

Diagram is highly exaggerated

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Determining the Location of the Shooter

Building is 60 feet away along the horizon line

Bullet hole is 4 feet above the ground

Where is the shooter located?

How to read a right triangle

o Sine, Cosine and Tangent are all based on a Right-Angled Triangle

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"Opposite" is opposite to the angle θ"Adjacent" is adjacent (next to) to the angle θ"Hypotenuse" is the long one

Adjacent is always next to the angleAnd Opposite is opposite the angle

Sine, Cosine and Tangent

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Sine Function: sin(θ) = Opposite / Hypotenuse

Cosine Function: cos(θ) = Adjacent / Hypotenuse

Tangent Function: tan(θ) = Opposite / Adjacent

Example: find the height of side d

Start with:sin 39° = opposite/hypotenuse =

d/30

Swap Sides: d/30 = sin 39°

Use a calculator to find sin 39°: d/30 = 0.6293…

Multiply both sides by 30:d = 0.6293… x 30 = 18.88 to 2

decimal places.

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