Chapter 17 Ballistics By the end of this chapter you will be able to: describe rifling on a gun barrel and explain how it marks a bullet explain barrel size and caliber 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 All Rights Reserved South-Western / Cengage Learning © 2009 Forensic Science: Fundamentals & Investigations, Chapter 17

Introduction Ballistics – the study of bullets and firearms. Firearms – weapon capable of firing a projectile using a confined explosive as a propellant. Ballistic evidence helps explain: What type of firearm was used. The caliber of the bullet. The number of bullets fired. Where the shooter was. Whether a weapon was fired recently. If a firearm was used in previous crimes. Forensic Science: Fundamentals & Investigations, Chapter 17

History of Gunpowder and Firearms The Chinese invented gunpowder (KNO3, charcoal, & sulfur) over a thousand years ago. Muzzle-loading matchlocks, the earliest firearms, used wicks to ignite the gunpowder. The cartridge (a case that holds a bullet, primer powder, and gunpowder) followed. Cartridges were loaded into the breech – the end of the barrel attached to the firing mechanism. Forensic Science: Fundamentals & Investigations, Chapter 17

Long Guns and Handguns Long guns, i.e. rifles and shotguns, require two hands for accuracy Rifles fire bullets; shotguns fire small, round pellets or a projectile called a slug. Handguns fired with one hand are called pistols Revolvers are pistols with a revolving cylinder that holds 6 cartridges Semiautomatics hold up to 10 cartridges in a magazine (clip). Semiautomatic fires one bullet per pull of the trigger. Fully automatic fires repeatedly as long as the trigger is pressed. Forensic Science: Fundamentals & Investigations, Chapter 17

Assignment Working in pairs or groups of three, research 5 different types of ammunition (not different calibers), describe each in terms of appearance and usage. Forensic Science: Fundamentals & Investigations, Chapter 17

Vocabulary Grooves – depressions Lands – ridges Both are found on the inside of a firearm’s barrel and are created when the firearm is manufactured Rifling – the spiral pattern of lands and grooves in the barrel of a firearm Forensic Science: Fundamentals & Investigations, Chapter 17

Firearms and Rifling Grooves and lands in the barrel of a gun produce the twisting that adds accuracy. This leaves a individualized pattern on the bullet. It is impossible to produce two identically rifled barrels Forensic Science: Fundamentals & Investigations, Chapter 17

Bullets, Cartridges, and Calibers Bullets and cartridges are packaged together. The bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind. Forensic Science: Fundamentals & Investigations, Chapter 17

Anatomy of a Cartridge Bullet – composed of lead, copper, or combination of other metals. Can be metal-jacketed, hollow-point, plastic coated Primer powder – initiates the contained explosion that pushes the bullet down the barrel Anvil and flash hole – provide the mechanism of delivering the explosive charge from the primer powder to the gunpowder. Headstamp – on bottom of cartridge identifies the caliber and manufacturer. Forensic Science: Fundamentals & Investigations, Chapter 17

How a Firearm Works Pulling the trigger causes the firing pin to hit the base of the cartridge, igniting the primer powder. The primer powder sparks through the flash hole to the main gunpowder supply. The main gunpowder supply ignites and the pressure of the explosion pushes the bullet from the casing into the barrel. The bullet follows the lands and grooves spiraling out of the barrel. Forensic Science: Fundamentals & Investigations, Chapter 17

Caliber of the Cartridge Caliber is a measure the diameter of the cartridge. These usually are hundredths of an inch. Common calibers include .22, .25, .357, .38, .44, and .45. Europe uses metric scale i.e. 9mm Caliber narrows down the type of gun used Forensic Science: Fundamentals & Investigations, Chapter 17

The Study of Bullets and Cartridge Casings Matching grooves (indentations) Matching lands (elevations) Investigators compare bullets and spent cartridges from a crime scene to those from the suspected firearm. Weapon is test-fired into water or a gel block so bullet is captured without damage. Forensic Science: Fundamentals & Investigations, Chapter 17

Marks on the Spent Cartridge Casings Firing pin marks on a spent cartridge can be used to match it to a firearm. The fire pin marks can appear on the rim or on the bottom of the spent cartridge. Breechblock marks are produced as the cartridge casing slams backward & strikes the breechblock. Other marks on spent cartridge casings are extractor and ejector nicks on semi and fully automatic weapons caused by loading and ejection of the cartridges Forensic Science: Fundamentals & Investigations, Chapter 17

Firing Pin Match Activity 17-2 in text. Pg 512-513 Copy table on page 513 and fill it in looking at the casings from three suspects Then make a list of all of the recovered bullets and the suspect it matches (A=2, B=1, etc) Answer Analysis questions and Further Study. Forensic Science: Fundamentals & Investigations, Chapter 17

Gunshot Residues (GSR) GSR - Particles of unburned powder and traces of smoke after gun is fired. They can leave a trace on the hand, arm, face, hair, or clothing of the shooter. They can also leave a trace on the victim. Chemical testing often can detect residue even if removal is attempted. The distance from the victim to the shooter can be determined by examination of the residue pattern on the victim. Forensic Science: Fundamentals & Investigations, Chapter 17

Databases Firearms databases can be used to match crime scene evidence to registered weapons National Integrated Bullet Identification System (NIBIS) records ballistics markings of firearms used in previous crimes Drugfire – FBI database that focuses on cartridge casings In 2000, they merged to form the National Integrated Ballistics Network (NIBIN) Forensic Science: Fundamentals & Investigations, Chapter 17

Database Opinion Paragraph Write a paragraph (at least 7 good, thoughtful sentences) about whether law enforcement should maintain a database of all firearms that are manufactured or sold in the U.S. Forensic Science: Fundamentals & Investigations, Chapter 17

Calculating Trajectory Trajectory – the path of the propelled bullet Helps determine where the shooter was located. If trajectory angle is downward, the shooter was positioned above the target. Two reference points along the flight path are needed to define the trajectory. Investigators can figure the shooter discharged the firearm somewhere along that line. Forensic Science: Fundamentals & Investigations, Chapter 17

Trajectory Reference points can be bullet holes in objects or victims. An entry point and exit point on a victim can be used. Gunshot residue or spent cartridge casings can be less specific reference points. Investigators can use lasers to trace a straight-line path to help determine the position of the shooter. Forensic Science: Fundamentals & Investigations, Chapter 17

Trajectory Can be difficult to determine Bullet can ricochet, become damaged, or does not provide a direct path for measurement. Targeting needs to be adjusted for very distant objects due to gravity. Forensic Science: Fundamentals & Investigations, Chapter 17

Path of bullet Horizon Wind shield Distance along path of bullet to window, 23.9” Distance along horizon to window, 23.5” y x 60 feet Trajectory Distance to the window = Distance to the shooter (x) Distance along horizon to window Distance to the building 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) Forensic Science: Fundamentals & Investigations, Chapter 17

Bullet Wounds Why do entrance wounds tend to be smaller than exit wounds? If the bullet penetrates clothing, fibers may be embedded in the direction of penetration GSR usually only found near entrance wounds. If gun is fired with the muzzle touching victim’s skin, the muzzle flash may burn the skin leaving a mark Forensic Science: Fundamentals & Investigations, Chapter 17

Bullet wounds Bullets may not travel smoothly through body; tumbling effect due to bones, organs and other tissues encountered High speed bullet are more likely to pass through Small caliber bullets tend to lodge within the body (less mass, not necessarily lower speed) Forensic Science: Fundamentals & Investigations, Chapter 17