1 Chapter 17 Ballistics By the end of this chapter you will be able to Explain the differences between a handgun a rifle and a shotgun Describe rifling on a gun barrel and how it affects the flight of the projectile ID: 670089
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Forensic Science: Fundamentals & Investigations, Chapter 17
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Chapter 17 Ballistics By the end of this chapter you will be able to:
Explain the differences between a handgun, a rifle, and a shotgunDescribe rifling on a gun barrel and how it affects the flight of the projectileExplain barrel size and caliber
All Rights Reserved South-Western / Cengage Learning © 2012, 2009Slide2
Forensic Science: Fundamentals & Investigations, Chapter 17
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Chapter 17 Ballistics By the end of this chapter you will be able to:
Describe how bullets are test fired and matched Discuss the role of ballistics recovery and examination at a crime scene Determine the position of the shooter based on bullet trajectory Slide3
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Introduction
Ballistics is the study of bullets and firearms.Ballistic evidence helps explain: What type of firearm was used The caliber of the bullet
The number of bullets fired Where the shooter was located
Whether a weapon was fired recently
If a firearm was used in previous crimes Slide4
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History of Gunpowder and Firearms
Chinese invented gunpowder over a thousand years agoMuzzle-loading matchlocks used wicks to ignite the gunpowderCartridge and breech loading
Revolver, semi-automatic, and automatic handguns
muzzleSlide5
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Modern firearms are divided into 2 basic groups:Long Guns and Handguns
Long gunsRifles fire bulletsShotguns fire pellets (shot) or a single projectile (slug)Both require the use of 2 hands for accurate firing.HandgunsPistols are fired with one hand
Revolvers have a cylinder (that
holds usually six
cartridges)
that turns as it is fired
The
Semiautomatic
is loaded with up to 10 cartridges into a magazine (clip); fire only 1 bullet per pull of the trigger
The
Fully Automatic
will fire repeatedly as long as the trigger is pressedSlide6
Pictures of Firearms
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Rifle
Shotgun
Revolver
Semiautomatic
Fully AutomaticSlide7
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Firearms and Rifling Grooves are indentations in the rifle’s barrel. The ridges (raised areas) that surround the grooves are called
lands.Grooves and lands in the barrel of a gun produce the twisting that adds accuracy. The spiral pattern of lands and grooves in the barrel of a firearm is called rifling
. This leaves a pattern on the bullet that matches the barrel pattern to a specific firearm.Slide8
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Bullets, Cartridges, and Calibers
Cartridge—a case that holds a bullet, primer powder, and gunpowder The bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind.
headstampSlide9
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How a Firearm Works
The primer powder sparks through the flash hole to the main propellant (gunpowder) supply.
Pull the trigger and the
firing pin hits the base of the cartridge, igniting the primer powder
mixture.Slide10
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How a Firearm Works
The bullet follows the lands and grooves pattern of the barrel and begins to spiral before it leaves the barrel.
The main gunpowder ignites, and the
pressure of the explosion pushes the bullet from the casing into the
barrel. Slide11
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Caliber of the Cartridge
Bullets (and their cartridges) are named by caliber and length.Caliber—a measure of the diameter of the cartridge—by hundredths of an inch. (Europeans use the metric system-9 mm)
Common calibers include: .22, .25, .357, .38, .44, and .
45
A .45 caliber cartridge measures 45/100 of an inch in diameter (almost ½ an inch).
Caliber also refers to the diameter of the inside of a firearm’s barrel; therefore, the caliber of ammunition should match the firearm that shoots it.
If a bullet is removed from a wound or crime scene, its caliber can link it to the weapon used to fire it.Slide12
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The Study of Bullets
and Cartridge Casings
How is each fired bullet marked? As a gun is fired, the barrel marks each bullet with its own unique pattern of lands and grooves.2. What is the procedure to match a spent bullet to the firearm that shot it?
Investigators compare bullets and spent cartridges shot from the suspected firearm. To get a known bullet for comparison, they test-fire the weapon.
What
makes up a test-firing, and why is it done?
Investigators test-fire the weapon into a water tank or gel block. This captures the bullet without damaging it. Then, they can compare the markings on known bullets with those on the suspect bullets.
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Marks on the
Spent Cartridge Casings Firing pin
marks—impressions made on the bottom of the cartridge by the firing pin as it strikes the bottom of the cartridge Appear on the rim or center of the spent cartridgeCan be used to match a cartridge to a firearm
Breechblock marks--produced when the cartridge casing slams backward and strikes the breechblock
The markings are unique to the firearm
Can be matched if the spent cartridge casings are foundSlide14
Marks (cont.)
Extractor marks--minute scratches produced as the cartridge is placed in the firing chamber (by the extractor)
Ejector marks--minute scratches produced as the cartridge is removed from the chamber (by the ejector)These marks are produced only in semiautomatic and fully automatic weapons In revolvers, cartridges are hand-fed into the revolving cylinder and have to be removed by hand as well
Forensic Science: Fundamentals & Investigations, Chapter 17 14Slide15
Databases
A searchable collection of information stored in a computer system
Firearms databases can be searched to match crime-scene evidence to registered weapons2 important databases:NIBIS—National Integrated Bullet Identification System (ballistic markings of firearms used in previous crimes)Drugfire—and FBI database (focuses on cartridge casings)
In 2000, these databases were merged to form NIBIN--National Integrated Ballistics Network15Slide16
How is NIBIS used to help solve crimes?
Law enforcement agents can use this database to see if they can match a bullet found at a crime scene to a firearm that was used to commit a crime in the past.
If this connection is made, how could this information help a law enforcement agent?Forensic Science: Fundamentals & Investigations, Chapter 17 16Slide17
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Gunshot Residues
Gunshot Residues (GSR)Particles of unburned powder and traces of smoke
Traces are left on the hand, arm, face, hair, or clothing of the shooter and/or victim (evidence)Chemical testing can detect residue even if removal (washing) is attempted
Distance from victim to shooter can be determined by examining the residue pattern on the victim
The amount of GSR decreases as the distance between firearm and victim increasesSlide18
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Trajectory Two reference points are needed to define the trajectory
Investigators canfigure the shooter discharged the firearm somewhere along that lineSlide19
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Trajectory Reference points can be
bullet holes in objects or victimsAn entry point and exit point on a victim Gunshot residue or spent cartridge casings Lasers can trace a straight-line path to determine the position of the shooterSlide20
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Trajectory and Gravity
Bullet’s path is slightly curvedGravity pulls it downward as the bullet moves forward
Diagram is highly exaggeratedSlide21
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Determining the Location of the Shooter
Building is 60 feet away along the horizon lineBullet hole is 4 feet above the ground
Where is the shooter located?Slide22
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TriangulationB is where the shooter is located; find the length of BCThe Abc triangle has the same proportions as the ABC triangleSo or
AB = 732.3” Slide23
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TriangulationUsing Pythagorean’s theorem AB2 = AC
2 + BC2732.32 = 7202 + BC2BC2 =
732.32 – 7202BC
2
=
536117 – 518400
BC = √17717
(square root)
BC = 133.1 inches
BC = 11.1 feet
We know that the bullet hole in the seat is four feet above the ground, so the shooter is 15.1 feet above the groundSlide24
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Bullet Wounds
– Questions to Discuss…
Examining body wounds can determine where a bullet entered and exited the victim, which help determine where the shooter was located by identifying the bullet’s path (or trajectory).Why do entrance wounds tend to be smaller than exit wounds?
If the bullet penetrates clothing, what can fibers embedded in the wound indicate?
Where
on the victim is
gunshot residue usually found?
If the gun is fired with the muzzle touching the victim’s skin, what telltale mark may show up?
Will larger or will smaller caliber bullets tend to lodge within the body rather than passing through? Why?
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Answers
Generally, the size of the entry would will be smaller than the bullet because skin in somewhat elastic (it stretches when a bullet enters the body). Exit wounds are generally larger because as the bullet moves through the body, it may collect and carry body tissue and bone with it.
Fibers imbedded in wounds can indicate the direction of penetration.Gunshot residue can be found only around entrance wounds.If the gun
is fired with the muzzle touching the victim’s skin, the hot gases released from the muzzle flash may burn the skin, leaving a telltale mark.High-speed bullets are more likely to pass through a body than are low-velocity bullets. Therefore, small-caliber bullets, such as a .22 caliber, tend to lodge within the body, while larger-caliber bullets will pass through.
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. . . . . . . . . . . . . Summary . . . .
Ballistics is the study of bullets and firearms.Firearms are divided into two groups—long guns and hand guns.Fired bullets show patterns of lands and grooves that match the rifling pattern in the barrel. A cartridge consists of primer powder, gunpowder, a bullet and the casing material.
The caliber of a cartridge usually is a measure of its diameter. Slide27
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. . . . . . . . . . . . . . . . . Summary
Investigators also check for firing pin, breechblock, extractor, and ejector marks.Gunshot residue can help recreate a crime. Using at least two reference points, an investigator can recreate a bullets trajectory and determine where the shooter was located. Examining body wounds can determine where a bullet entered and exited the victim.