1. Ballistics By the end of this unit you will be able to:
Explain the differences between a handgun, a rifle, and a shotgun
Know the series of events in the gun which cause the bullet to leave the barrel.
Describe unique markings that may be used to identify bullets or guns used in cases.
Lands and grooves
Rifling
Firing pin impressions

2. Ballistics
Describe how bullets are test fired and matched in the laboratory
Discuss the role of ballistics recovery and examination at a crime scene
Determine the position of the shooter based on bullet trajectory

3. Introduction 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

4. Review Firearms and Rifling
Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracy
This leaves a pattern on the bullet that is unique

5. Review: 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.

6. Review: How a Firearm Works
The firing pin hits the base of the cartridge, igniting the primer powder
The primer powder sparks through the flash hole to the main propellant supply
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

7. Caliber of the Cartridge
Caliber—a measure of the diameter of the cartridge
In hundredths of an inch
Common calibers include .22, .25, .357, .38, .44, and .45
Why should the caliber of ammunition match the firearm that shoots it?
If they do not match, what could go wrong?

8. Review: The Study of Bullets and Cartridge Casings
How is each fired bullet marked?
What is the procedure to match a spent bullet to the firearm that shot it?
What makes up a test-firing, and why is it done?

9. Review: Marks on the Spent Cartridge Casings
Evidence found at a crime scene
Firing pin marks
appear on the rim or center of the spent cartridge
can be used to match a cartridge to a firearm

10. IBIS Integrated Ballistic Identification System
Program controlled by the ATF (Bureau of Alcohol, Tobacco, & Firearms)
Software and program which produces a digital history of bullets,casing,and cartridges.
FBI and ATF joined forces and use a super powered computer now to track ballistic evidence left at crime scenes .

11. Gunshot Residues 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
Chemical testing can detect residue even if removal is attempted
3 elements :lead, antimony, & barium; all 3 must be present to be used in court

12. How a spectrophotometer works
Spectrophotometer is the name of a machine which can identify elements and the amounts of each element to create a spectrum chart.
Location on X-axis ID’s type of element
Height of peak shows concentration

13. Distance Identification
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.

14. Wound Patterns 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

15. Trajectory Two reference points are needed to define the trajectory
Investigators can figure the shooter discharged the firearm somewhere along that line

16. Trajectory 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
Lasers can trace a straight-line path to determine the position of the shooter

17. Trajectory and Gravity
Bullet’s path is slightly curved
Gravity pulls it downward as the bullet moves forward
Diagram is highly exaggerated

18. 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?

19. How to read a right triangle
Sine, Cosine and Tangent are all based on a Right-Angled Triangle
"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 angle
And Opposite is opposite the angle

20. Sine, Cosine and Tangent
Sine Function:
sin(θ) = Opposite / Hypotenuse
Cosine Function:
cos(θ) = Adjacent / Hypotenuse
Tangent Function:
tan(θ) = Opposite / Adjacent

21. 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 = …
Multiply both sides by 30:
d = … x 30 = to 2 decimal places.