1. Firearms and Toolmarks

2. Firearms Summary Guns (types and manufacturing) Ammunition
Firing a gun
Collecting Evidence
Analyzing Evidence

3. Firearms
Types of Guns

4. Types of Barrels Smooth Barrel: Hollow tube
Firearms
Types of Barrels
Smooth Barrel: Hollow tube
Rifled Barrel: Barrel of gun can be rifled to put spin on bullet; increases accuracy

5. Rifled Barrel Inside of barrel has hills (lands) and valleys (grooves)
Firearms
Rifled Barrel
Lands
Inside of barrel has hills (lands) and valleys (grooves)
Lands and grooves twist down length of gun
Grooves

6. Rifled Barrel Inside of barrel has hills (lands) and valleys (grooves)
Firearms
Rifled Barrel
Inside of barrel has hills (lands) and valleys (grooves)
Lands and grooves twist down length of gun

7. Rifled Barrel (manufacturing)
Firearms
Rifled Barrel (manufacturing)
Begin with a hollow tube
Lands and grooves made by forcing cutting tools through the tube.

8. Rifled Barrel (manufacturing)
Firearms
Rifled Barrel (manufacturing)
The minor differences in manufacturing leads to differences in the scratches (striations) on the fired bullet.

9. Handgun Designed to be held and fired with one hand Firearms Revolver
Semiautomatic pistol

10. Revolver Hammer pulled back manually or when trigger is pulled
Firearms
Revolver
Hammer
Bullets
Hammer pulled back manually or when trigger is pulled
Hammer hits back of bullet casing; causes explosion
Barrel rifled
Trigger

11. Semiautomatic pistol Hammer strikes bullet case when trigger pulled
Firearms
Semiautomatic pistol
Bullets
Hammer
Hammer strikes bullet case when trigger pulled
Bullet casing automatically ejected.
Barrel rifled
Trigger

12. Rifle Hammer strikes bullet case when trigger pulled
Firearms
Rifle
Hammer strikes bullet case when trigger pulled
Bullets
Bullets
Hammer
Bullet casing manually or automatically ejected.
Barrel rifled; fires bullet
Trigger

13. Shotgun Hammer strikes shotshell when trigger pulled
Firearms
Shotgun
Projectile
Hammer strikes shotshell when trigger pulled
Bullet casing manually or automatically ejected.
Barrel smooth; fires shot or slug
Trigger

14. Ammunition (Bullets) Firearms > Ammunition Bullet Cartridge
Propellant (inside cartridge)
Primer

15. Ammunition (Types of Bullets)
Firearms > Ammunition
Ammunition (Types of Bullets)
Lead or Lead Alloy: softer bullet; scraped up by the lands and grooves of barrel
Semijacketed bullet: brass jacket covers sides of lead bullet, except for tip
Bullet expands on impact
Jacket not scraped up as much
Jacket can be shed after hitting target

16. Ammunition (Types of Bullets)
Firearms > Ammunition
Ammunition (Types of Bullets)
Full Metal Jacket: lead core completely covered with brass

17. Fires many small round pellets
Firearms > Ammunition
Shotgun Shell
Shot (pellets)
Cartridge
Wad (plastic)
Propellant (inside cartridge)
Primer
Fires many small round pellets

18. Primer When hit with hammer, primer creates a small explosion
Firearms > Ammunition
Primer
When hit with hammer, primer creates a small explosion
This explosion lights propellant creating a large explosion (propels bullet)

19. Firearms > Ammunition
Propellant
Modern propellants are smokeless powders composed of nitrocellulose
Some contain nitrocellulose and nitroglycerin

20. Collection of Firearms evidence
Firearms > Collection
Collection of Firearms evidence
Important marks on the outside of the bullet can be damaged during collection.
Either collect the item containing embedded bullet or…
Use rubber coated forceps to remove bullet

21. Firearms > Collection
Fired Bullets

22. Collection of Firearms evidence
Firearms > Collection
Collection of Firearms evidence
Bullets and cartridges should probably not be physically marked by investigator.
Marks may damage important striations
Small evidence should be collected in sealed and marked containers
Pillbox, glass vials

23. Analysis of Firearms evidence
Firearms > Analysis
Analysis of Firearms evidence
Class Characteristics of bullets:
Caliber (size)
# of lands/grooves
Direction of rifling twist
Degree of twist
Width of lands/grooves

24. Analysis of Firearms evidence
Firearms > Analysis
Analysis of Firearms evidence
Class Characteristics of cartridges
Caliber (size)
Firing pin location
Firing pin size/shape
Extractor/ejector sizes
Relative location of extractor/ejector

25. Analysis of Firearms evidence
Firearms > Analysis
Analysis of Firearms evidence
If class characteristics of fired bullet and suspected gun match, a test bullet is fired for further analysis.

26. Comparison microscope is used to compare striations on bullets.
Firearms > Analysis
Comparison microscope is used to compare striations on bullets.

27. Comparison of Striations
Firearms > Analysis
Comparison of Striations
Striations – tiny scratches on bullet that can be specific to a single gun.

28. Conclusions of analysis
Firearms > Analysis
Conclusions of analysis
If class characteristics and striations match, can say the bullet was likely fired by the suspect gun.
If class characteristics (and striations) do not match, the suspect gun can be excluded.
If class characteristics match but striations do not, the results are inconclusive.

29. Range-of-fire estimation
Firearms
Range-of-fire estimation
The distance between the gun and victim can be estimated by looking at gunshot residue patterns
Long distance: no GSR on the victim
Close-range: GSR on victim - spread out
Near-contact: GSR on victim - concentrated circle
Contact shot: “Blown out” entrance wound

30. Tool Marks
Tools make specific marks when they cut or scrape a softer surface
Compression tool mark: shows outline of tool (hammer into wood)
Sliding tool mark: parallel striations when tool slides across material (screwdriver or crowbar)
Cutting tool mark: striations when tool cuts through material (scissors)

31. Tool Marks

32. Collection of Tool Marks
Notes, sketches, photographs
If possible, the tool mark should be taken back to the lab.
If not, a cast should be made.
Silicone rubber ideal material

33. Conclusions of analysis
Firearms > Analysis
Conclusions of analysis
If class characteristics and striations match, can say the tool mark was likely made by the suspect.
If class characteristics (and striations) do not match, the suspect tool can be excluded.
If class characteristics match but striations do not, the results are inconclusive.