1. 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
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Forensic Science: Fundamentals & Investigations, Chapter 17

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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