1. Unit 5: Firearms, Tool Marks, and Other Impressions
Mr. Ross Brown
Brooklyn School for Law and Technology

2. How can we determine the firearm from which a bullet was shot?
18 April 2016
Do now: What makes it difficult to determine which firearm shot a specific bullet?

3. In this unit we will learn about:
How to compare bullets
Information we can gather from cartridge cases
Gunpowder residues
Primer residues on the shooter’s hands
Firearm serial numbers
Tool marks
Other impressions

4. How can we determine the firearm from which a bullet was shot?
Just as fingerprints can tell us apart, inanimate objects also have specific markings
Scratches, nicks, wear patterns
Firearms identification

5. How can we determine the firearm from which a bullet was shot?
Bullet markings
Gun barrels are rifled, or created with grooves
Grooves give a fired bullet spin so it flies true

6. How can we determine the firearm from which a bullet was shot?

7. How can we determine the firearm from which a bullet was shot?
Caliber is the diameter of a gun barrel measured between lands
Typically in hundredths of an inch or millimeters

8. How can we determine the firearm from which a bullet was shot?
19 April 2016
Do now: In addition to rifling marks, what other markings identify the weapon which fired a bullet?

9. How can we determine the firearm from which a bullet was shot?
Lands: raised portion between grooves in a rifled barrel
Grooves: Low-lying portion between lands
Rifling: Spiral grooves formed or cut into the barrel of a rifle or gun to spin the projectile

10. How can we determine the firearm from which a bullet was shot?

11. How can we determine the firearm from which a bullet was shot?
Cartridge cases
Just as bullets show deformation, so too do cartridge cases from contact with metal surfaces

12. How can we determine the firearm from which a bullet was shot?

13. How can we determine the firearm from which a bullet was shot?

14. What else can we use to identify a weapon used in a crime?
21 April 2016
Do now: Why is gunpowder residue an important piece of evidence?

15. What else can we use to identify a weapon used in a crime?
How a bullet works

16. What else can we use to identify a weapon used in a crime?
Gunpowder residue
Helps determine firing-distance
How far away was the shooter? Could this have been self-defense?

17. What else can we use to identify a weapon used in a crime?
Primer residue on hands
Used to put hot wax on the suspected shooter’s hands to find nitrates (in the gunpowder)
Today, we test for chemicals only found in the primer

18. What else can we use to identify a weapon used in a crime?
Serial number restoration
The pressure applied while grinding the number in fact presses it into the body of the weapon
Acid can etch out this weakened metal

19. What else can we use to identify a weapon used in a crime?
Considerations when collecting firearms evidence
Safety!
Mark bullets for identification, but only on nose or base to protect rifling marks
Of course, everything tagged, numbered, etc
Bring to lab quickly