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3/18/2013

Chapter 17 By the end of this chapter you will be able to: Introduction

Ballistics – the study of and .  describe on a barrel and explain how it marks a Firearms – capable of firing a using a confined explosive as a .  explain barrel size and Ballistic evidence helps explain:  describe how bullets are test fired and matched  What type of was used.  discuss the role of ballistics recovery and examination at a crime scene  The caliber of the bullet.  The number of bullets fired.  determine the position of the shooter based on bullet trajectory  Where the shooter was.  Whether a weapon was fired recently. All Rights Reserved South-Western / Cengage Learning © 2009  If a firearm was used in previous crimes. 1 Forensic Science: Fundamentals & Investigations, Chapter 17 2 Forensic Science: Fundamentals & Investigations, Chapter 17

History of and Firearms Long and

 Long guns, i.e. and , require two hands  The Chinese invented gunpowder (KNO3, for accuracy charcoal, & sulfur) over a thousand years  Rifles fire bullets; shotguns fire small, round pellets or ago. a projectile called a .  Muzzle-loading , the earliest  Handguns fired with one hand are called firearms, used wicks to ignite the gunpowder.  are pistols with a revolving that holds 6 cartridges  The (a case that holds a bullet,  Semiautomatics hold up to 10 cartridges in a powder, and gunpowder) followed. ().  Cartridges were loaded into the breech – the  Semiautomatic fires one bullet per pull of the . end of the barrel attached to the firing  Fully automatic fires repeatedly as long as the trigger mechanism. is pressed. 3 4 Forensic Science: Fundamentals & Investigations, Chapter 17 Forensic Science: Fundamentals & Investigations, Chapter 17

Assignment Vocabulary

 Grooves – depressions  Working in pairs or groups of three, research  Lands – ridges 5 different types of (not different  Both are found on the inside of a firearm’s ), describe each in terms of barrel and are created when the firearm is appearance and usage. manufactured  Rifling – the spiral pattern of lands and grooves in the barrel of a firearm

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Firearms and Rifling Bullets, Cartridges, and Calibers

 Grooves and lands in the barrel of a gun produce the twisting that adds accuracy. Bullets and cartridges are packaged together.  This leaves a individualized pattern on the bullet. The bullet, usually of metal, is out front  It is impossible to produce two identically rifled with the cartridge, holding the primer and barrels propellant powders, behind.

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Anatomy of a Cartridge How a Firearm Works

 Bullet – composed of lead, copper, or 1. Pulling the trigger causes the to hit combination of other metals. Can be metal- jacketed, hollow-point, plastic coated the base of the cartridge, igniting the primer powder.  Primer powder – initiates the contained explosion that pushes the bullet down the barrel 2. The primer powder sparks through the flash hole to the main gunpowder supply.  Anvil and flash hole – provide the mechanism of delivering the explosive from the primer 3. The main gunpowder supply ignites and the powder to the gunpowder. pressure of the explosion pushes the bullet from the casing into the barrel.  – on bottom of cartridge identifies the caliber and manufacturer. 4. The bullet follows the lands and grooves spiraling out of the barrel. 9 Forensic Science: Fundamentals & Investigations, Chapter 17 10 Forensic Science: Fundamentals & Investigations, Chapter 17

The Study of Bullets and Caliber of the Cartridge Cartridge Casings

Matching lands (elevations)  Caliber is a measure the diameter of the cartridge. Matching  These usually are hundredths of an inch. grooves (indentations)  Common calibers include .22, .25, .357, .38, .44, and .45. Europe uses metric scale i.e.  Investigators compare bullets and spent 9mm cartridges from a crime scene to those from  Caliber narrows down the type of gun used the suspected firearm.  Weapon is test-fired into water or a gel block so bullet is captured without damage.

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Marks on the Spent Cartridge Casings Firing Pin Match

 Firing pin marks on a spent cartridge can be used  Activity 17-2 in text. Pg 512-513 to match it to a firearm.  Copy table on page 513 and fill it in looking  The fire pin marks can appear on the or on the bottom of the spent cartridge. at the casings from three suspects  marks are produced as the cartridge  Then make a list of all of the recovered casing slams backward & strikes the breechblock. bullets and the suspect it matches (A=2, B=1,  Other marks on spent cartridge casings are etc) and ejector nicks on semi and fully  Answer Analysis questions and Further automatic caused by loading and ejection of the cartridges Study.

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Gunshot Residues (GSR) Databases

 GSR - Particles of unburned powder and traces of  Firearms databases can be used to match smoke after gun is fired. crime scene evidence to registered weapons  They can leave a trace on the hand, arm, face, hair,  National Integrated Bullet Identification or clothing of the shooter. System (NIBIS) records ballistics markings of  They can also leave a trace on the victim. firearms used in previous crimes  Chemical testing often can detect residue even if  Drugfire – FBI database that focuses on removal is attempted. cartridge casings  The distance from the victim to the shooter can be determined by examination of the residue pattern on  In 2000, they merged to form the National the victim. Integrated Ballistics Network (NIBIN)

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Calculating Trajectory Trajectory

 Trajectory – the path of the propelled bullet  Reference points can be bullet holes in objects  Helps determine where the shooter was located. or victims.  If trajectory angle is downward, the shooter was  An entry point and exit point on a victim can be positioned above the target. used.  Two reference points along the flight path are  residue or spent cartridge casings can needed to define the trajectory. be less specific reference points.  Investigators can figure the shooter discharged  Investigators can use lasers to trace a straight- the firearm somewhere along that line. line path to help determine the position of the shooter.

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Wind shield

Distance along path of Path of bullet bullet to window, 23.9” x y Trajectory Trajectory 60 feet Horizon Distance along horizon to window, 23.5”

 Can be difficult to determine  Bullet can ricochet, become damaged, or do not provide a direct path for measurement. Distance to the window = Distance to the shooter (x) Distance along horizon to window Distance to the building  Targeting needs to be adjusted for very distant objects due to gravity.  With the distance to the building and the distance to the shooter along the trajectory of the bullet, the Pythagorean theorem can be used to determine the height of the shooter above the horizon (not the ground)

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Bullet Wounds Bullet wounds

 Why do entrance wounds tend to be smaller  Bullets may not travel smoothly through than exit wounds? body; tumbling effect due to bones, organs  If the bullet penetrates clothing, fibers may be and other tissues encountered embedded in the direction of penetration  High speed bullet are more likely to pass  GSR usually only found near entrance wounds. through  If gun is fired with the muzzle touching victim’s  Small caliber bullets tend to lodge within the skin, the may burn the skin leaving a mark body (less mass, not necessarily lower speed)

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