1. Firearms and Ballistics
Mrs. Schultz

2. Forensic examiners are most likely to run into:
Handguns
Shotguns
Rifles
Submachine guns

3. A Casing in Cross-Section

4. Parts of a Handgun

5. Parts of a Shotgun

6. Parts of a Rifle

7. Submachine Gun

8. Ballistics is the study of bullet motion
Internal Ballistics: The events that transpire within the firearm such as the striking of the firing pin and the scratching of the bullet by the rifling or by striations.
External Ballistics: The events that transpire after the bullet leaves the gun but before it hits the target. These events help determine where the perpetrator was standing in relation to the victim.
Terminal Ballistics: Refers to what happens when the bullet hits the target. Medical examiners can determine whether the bullet passed front to back or back to front.

9. We will look in more detail at internal ballistics.

10. Firearm Accuracy Accuracy improves by lengthening the barrel.
The barrel is made by boring through a solid rod of steel. The drill leaves marks on the steel, individualizing the barrel.
Adding grooves in the bore causes the bullet to spin, improving accuracy. Spiral grooves are called rifling. Different manufacturers use different groove patterns. Those grooves leave marks on bullets, individualizing bullets.

11. This barrel has 8 grooves

12. Do you notice the rifling differences in these two guns?
Would bullets coming out of these two guns looks different?

13. Caliber is measured from a land on the left to a land on the right
Caliber is measured in hundredths of an inch, such as a .38 caliber gun
For European guns, caliber is measured in millimeters, such as a 9mm hand gun

14. The bigger the caliber the bigger the……U L E T

15. Class vs. Individual Characteristics
The number of lands and grooves, and their direction and rate of twist are characteristic of a particular product from a specific manufacturer. The marks the lands and grooves leave on bullets are class characteristics. Examiners can tell what type of gun fired the bullet but can’t identify a particular gun.
As grooves are cut through the barrel, the broach cutter leaves fine lines, called striations. Striations are unique and are therefore individual characteristics.

16. Cut away of the Inside of a barrel
Broach cutter
Cut away of the Inside of a barrel

17. Striations on a crime scene bullet and on one test fired from the recovered gun

18. Bullets are often damaged when they hit their target
Watch for inaccuracies in crime shows….how often do they recover a perfect bullet from a victim?
This rifle bullet was recovered from a deer who was shot in North Carolina.

19. What if there is no bullet
What if there is no bullet? What else might be left at a crime scene involving a firearm?

20. What happens when a gun is fired?
The bullet is enclosed in a cartridge/shell/casing.
The firing pin (hammer) strikes the primer. The primer holds a small amount of shock sensitive explosive mixture.
The primer material explodes, causing gunpowder to explode.
The expanding gases cause the bullet to shoot out of the barrel.
The breechblock prevents the spent cartridge from leaving the gun.
The spent cartridge/shell casing is extracted from the chamber and ejected from the gun.

23. What a shell can tell…
Shell casings can give class characteristics such as manufacturer and caliber.
What type of gun fired the bullet that was in this casing?

24. What about this casing?

25. What a shell can tell…
Individual characteristics are formed on shells from
the firing pin, the breechblock, and the extractor
and ejector mechanism that removes the shell.

26. IBIS Cartridge Match (Integrated Ballistic Identification System)

27. Breechblock Comparison Parallel vs. Circular

28. Crime scene cartridge extractor marks

29. Test cartridge extractor marks

30. Matching extractor striations on crime scene cartridge and test cartridge

31. What else can forensic scientists do?

32. Serial number restoration

33. Serial number restoration
Licensed gun dealers must keep records of serial numbers and the name of the person who purchased a particular gun.
Studies have shown that 15% of guns recovered by police have had their serial numbers removed.
Serial numbers can be restored through two methods: Magnaflux method and acid etching method.

34. Magnaflux Method Works on serial numbers imprinted in iron or steel.
Grind smooth the obliterated surface.
Attach a magnet to the opposite side.
Add a mixture of iron filings and oil to the obliterated mark.
The metal filings arrange themselves in a shadow of each number.

35. Acid Etching Method
Works on serial numbers imprinted in iron or aluminum.
Grind smooth the obliterated surface.
Add Fry’s reagent, Vinella’s reagent, or Hume-Rothery solution. Scratches will dissolve away.
Once the number is visible, the acid will continue to react, so photograph quickly.
Etching cannot be done a second time.

36. Forensic Scientists Can Also Check For Gun Shot Residue (GSR)

37. What part of the hand will most likely test positive?
The back of the hand and the webbing between the thumb and forefinger

38. GSR can help scientists determine distance from shooter to target
A LOT of variables come into play. Look at the pattern difference below.

39. In general, you can expect:
If the gun is in contact or less than 1 inch from target, you will see a heavy concentration of vaporous lead around the bullet hole

40. In general, you can expect:
If the gun was inches away, you will see a halo of vaporous lead and scattered specks of burned and unburned gunpowder.
This bullet hole was made by a gun fired 15 inches away

41. In general, you can expect:
If the gun is over three feet away, you will see a dark ring around the bullet entrance, called a bullet wipe.
This bullet hole was made by a gun fired from 10 feet away

42. Contact Shot Distance Animation

43. To test if someone fired a gun
Look for lead, barium, or antimony on hand swabs.
This can be complicated because residue is only on the hand for a short amount of time. Some labs won’t work with samples taken 6 or more hours after the suspected firing incident.
The swab can be tested with neutron activation analysis, flameless atomic absorption spectrophotometry or with an SEM linked to an X-ray analyzer.

44. The Greiss Test
Involves testing for nitrites around bullet holes by pressing a chemically treated gelatin-coated photographic paper to the target surface and then applying heat.