1. Ballistics

2. Job of Firearms Examiner
Analyze bullets/casings to determine the type of weapon used
Match bullet/casing to a specific weapon
Match bullet/casing to a sample from another crime
Crime scene reconstruction
a) distance between muzzle and victim
b) bullet trajectory

3. Ballistics
Ballistics is the science of the travel of a projectile in flight.
The flight path of a bullet includes:
Travel down the barrel
Path through the air
Path through a target

4. How a gun fires Pull trigger
Firing pin strikes a cylinder of primer in the shell of the bullet
Explosion pushes bullet through the gun’s barrel

5. Types of Guns Handguns a. revolver b. semiautomatic pistols
c. machine pistols (automatics)
Rifles
Shotguns

6. Handguns: Revolver Think westerns Cartridge revolves
Casing stays in cylinder
Limited to six shots
More accurate than semiautomatics

7. Handguns: Semiautomatic Pistols
Loaded using magazine or clip
Carry rounds
Clip is spring loaded
Fires once for each pull of the trigger
Empty case ejected

8. Automatic Weapons (machine pistols)
Fire repeatedly as long as the trigger is depressed

9. Rifles
Use a lever or sliding bolt to eject a spent cartridge and move next one into firing chamber
More accurate and shoot more powerful cartridges than handguns

10. Comparison of Handgun and Rifle Bullets
The metal casing encloses the powder, above which the bullet is seated.
The powder is ignited through the flash hole when the primer is struck
A case with a rim is found with revolver and lever action rifle cartridges, and also with some bolt action and semi-automatic rifles.

11. Shotguns Fire shells filled with pellets (shot)
Shot spreads out in circular pattern
Have no “rifling” inside the barrel
Note: “rifling” are the spiral grooves inside the gun barrel that make
the bullets spin.

12. Diagram of a Shotgun Shell
At close range, the pellets (shot) act as one mass. The entrance wound would be about 1 inch in diameter and the wound cavity would contain wadding.
At intermediate range (4-12 feet) the entrance wound is 2 inches in diameter and individual pellet markings are seen.
Most pellets will not penetrate skin beyond 80 yards.

13. Intermediate range gunshot wound

14. Analyzing Bullets
Always handle bullets carefully when collecting from a crime scene
A bullet pried from a doorjamb, for example, should be checked for attached paint, fibers, or flesh
Bullets removed from a body should be handled with surgical instruments during surgery

15. Types of bullets Low velocity – softer High velocity – harder
Bullet shape is important in the wounding potential of the bullet

16. Lead Bullets
Used in small caliber handguns and .22 and .25 caliber rifles They are soft and have less penetration

17. Lead Alloy Bullets
These lead bullets have other metals added for hardness
High velocity

18. Semi-Jacketed Bullets
Have a thin brass coating
Lead nose exposed
May have a hollow point

19. Full Metal Jackets Completely covered w/ copper
They are very high velocity
bullets used by the military
45 AUTO,
230 grain full-metal
-jacketed bullet. . .

20. Caliber Refers to the internal diameter of the barrel
Measured in inches or mm
Ex: .38 handgun –diameter of .38 inches

21. Shotgun Gauge Number of lead balls that it takes to weigh one pound
Ex. 20 gauge shotgun:
20 lead balls = one pound

22. Marks Left on Casings
1. Impression left by firing pin a. center fire (primer in a cup) b. rim-fire (primer around the edge) 2. Breechblock patterns

23. Marks left on casing 3. Headstamps- info stamped by manufacturer
4. Extractor and ejector marks
on side of casing
automatic and semiautomatic weapons
extractor: pulls next bullet into place
ejector: push spent shell from weapon

24. Rifling Rifling refers to the spiral grooves etched inside the barrel
They leave marks (striations) on bullets.
Lands- high parts
Grooves- low parts:
Smooth bore rifles (shotguns) have no rifling and are not as accurate

25. Different gun types have different characteristics in their rifling Ex Caliber Colt 6 lands and grooves with a left (counterclockwise) twist
Ex. .32 caliber Smith and Wesson handgun
5 lands and grooves with a right (clockwise) twist.

26. Rifling
FBI database keeps general rifling characteristic files for all weapons
Machine that does the rifling becomes worn with use so each barrel is different

27. Rifling Firing of a gun wears down lands and grooves
first bullet fired will have different striations than 100th bullet fired
To confirm a match you need identical patterns on at least three consecutive striations on each bullet

28. Bullet patterns
Patterns of Striations on Bullets

29. How to Make a Comparison
Get an intact bullet from suspect weapon
Fire bullet using the suspect weapon into a test firing chamber
Compare lab-fired bullet to crime scene bullet using a comparison microscope

30. Databases
Databases can be used if a suspect weapon is not available for comparison. The databases most commonly used are:
IBIS- Integrated Bullet ID system (ATF)
can connect two or more cases
DRUGFIRE- FBI, focuses more on shell casings
An expert makes the final match, not the computer.

31. Gunshot Residue (GSR)
GSR occurs when gases and particulate matter escape through openings in the weapon and cling to hands, arms, clothing, face, walls, or the victim
Pattern affected by wind, rain
GSR can aid in distinguishing entrance from exit wounds (entrance will have more GSR)
It can also help determine who fired a weapon—since it will appear on the shooter’s hands

32. GSR -Gunshot residue
Soot on hand of a suicide victim, giving an indication that he was holding the weapon when it was fired

33. Griess Test Griess test is used to detect GSR
Photographic or acetic acid paper is pressed over the area and soaked in reagent that will show the pattern of GSR
Fades in 2 hours
Detects byproducts of combustion such as lead, barium, antimony

34. Griess test

35. Gunshot residue
Other testing is done by a swab of the area with filter paper
Treat the paper with diphenylamine : ID metals by undergoing a color change. (blue is a positive result)
False positives can be caused by: fertilizer, tobacco, cosmetics, urine
Need confirmatory testing

36. Gunshot residue
SEM- (scanning electron microscope) detects tiny GSR particles that have been exposed to high temp, are melted, and deformed

37. Determining Distance
How GSR affects the wound area varies with the distance from the shooter to the victim
Residue pattern on skin or clothing changes w/ distance
Generally speaking, the more distance between the shooter and the victim, the wider the spread of GSR

38. Determining distance
Test by use the suspect weapon on similar fabric at various distances such as:
6 inches, 1 ft, 18 inches, 2 ft, 3 ft
Compare to victim’s clothing for match

39. Mechanism of ballistic injury

40. Gunshot Wounds Gunshot wounds are typically classified as
Contact —have soot on the outside of the skin, and muzzle imprint, or laceration of the skin from effects of gases. (Close range = less than 6”)
Intermediate range —show a wide zone of powder stippling, but lack a muzzle imprint and laceration. (6”-30”)
Distance range —lack powder stippling and usually exhibit a hole roughly the caliber of the projectile fired. (greater than 30”)

41. The upper diagram illustrates the basic differences between the skin appearance of a contact, close (intermediate), and distant (indeterminant) range gunshot wound. The appearance of the wounding characteristics in the skull is shown in the lower diagram in which there is bevelling of the skull outward away from the direction of origin of the bullet.

42. Entrance wound on the left
Exit wound on the right—vary in size and shape because the bullet can be deformed as it passes through the body. No exit wound means all the bullet’s energy was absorbed by the tissues.

43. Gunshot entrance wound to skull—notice heavy soot and radiating fracture lines

44. Exit wound
No soot or powder, wound is a slit

45. Blood spatter
Blood collects on hand of shooter

46. Terminal ballistics

47. Websites http://www.firearmstactical.com/wound.htm
excellent: tons of photos
great case studies with photos

48. Shot Number 12 shot .05 inches smallest Number 8 shot Number 4 shot
largest