1. Types of Firearms May be classified by their state of automation
single-shot (manual)
semiautomatic
automatic
May also be classified by aspects of their physical design
Rifled
Smoothbore

2. Handguns Designed to be fired with one hand
originally designed for cavalrymen who could only spare one hand from the reins of the horse
There are some single-shot handguns used for specialized target shooting
Handguns with revolving cylinders are called revolvers

3. A Colt .45

4. Rifles Designed to be fired with two hands, usually from the shoulder
There are some small bore sporting rifles that are single shot
Most are semiautomatic or automatic
redirect the energy from either the bullet recoil or hot propellant gases to extract & eject the cartridge casing, then cock & load a new bullet
Assault rifles may be used either in semi-automatic or automatic mode

5. Bullet Morphology

6. Cartridge Cases
Cutaway photos of three kinds of cartridge cases

7. Firing A Shot Chambered bullet
Firing pin hits primer & sending a flash to ignite the powder
Bullet is propelled forward though the gun barrel as the spent cartridge case is slammed back against breechblock

8. Smoothbore Firearms
Shotguns are the only smoothbore small arm currently in use
Fire multiple small projectiles (pellets or shot) so accurate aiming not an issue
barrels smooth rather than rifled
barrels shaped or indented to control the spread of the shot as it exits the muzzle
choke

9. Compression Formed Shotgun Shell
Pellets are separated from the propellant by one or more overpowder wads
seal the propellant gases behind the shot

10. The Rifled Barrel
Has a series of spiral cut-outs that run the length of the barrel
depressions
grooves
raised portions
lands

11. Interior View of a Rifled Gun Barrel
Horizontal striations on the grooves (G) come from the rifling process
Vertical striations on the lands (L) come from the initial reaming of the barrel
These markings impress the bullet as it travels through the barrel

12. Barrel Manufacture
Before 1940, grooves cut one at a time by drawing a scraper repeatedly down the inside of the barrel as it was rotated
Three modern methods of rifling
broaching
button rifling
hammer forging

13. Broaching
The diameter of the hole reamed in the steel will be the final diameter (caliber) of the barrel
Grooves cut with a tool called a gang broach
consists of a series of circular cutting tools with projecting teeth positioned a regular intervals on a rod

14. Broaching
The teeth cut away the metal in the grooves as the broach is forced through the barrel by hydraulic pressure
Successive cutting disks increase in diameter until the desired groove depth is reached

15. Bore Diameter of Rifled Barrels
Measured from the tops of opposing lands when there is an even number of lands & grooves
measured from a circle tangent to the tops of the lands if there is an odd number of lands & grooves

16. Bore Diameter
All firearms may be characterized by their bore diameter or caliber
the measure of the diameter in hundredths of an inch or in millimeters
American & British weapons are normally given in hundredths of an inch (.22; .45)
other countries are normally in mm (9 mm)
The larger the number, the larger the diameter
.22 is smaller than .45

17. Rifled Barrel
The # of lands & grooves; their direction & rate of twist are characteristic of a particular product from a specific manufacturer
class characteristics
Examples
.32 caliber Smith & Wesson revolvers
5 lands & grooves twisting to the right
.32 caliber Colt
6 lands & grooves twisting to the left

18. Firing Pin (Primer Pin)
Strikes the cartridge primer to initiate the firing process
Finished on a lathe or filing by hand
Can transfer striations to the soft metal of the primer cap

19. Primers
Since gunpowder is relatively stable, it I ignited via a more flammable or explosive primer
Types of systems
rimfire cartridge
primer placed in the rolled rim of the cartridge casing
centerfire cartridge

20. Some Rimfire Impressions

21. Firing Pin Match

22. How A Bullet Acquires Rifling Impressions

23. Bullet Comparisons
One bullet is rotated until a well-defined land or groove comes into view
The other bullet is then rotated in search of a matching region
Analyst must allow for distortion between bullets due to mutilation on impact

24. Moving Components
Some components of a firearm’s firing & cartridge ejection mechanism are of importance to the forensic examiner
the breechblock
the firing pin
the extractor
the ejector

25. Ammunition
Construction

26. Extractor & Ejector Extractor Ejector
extracts a spent cartridge from the chamber
Ejector
ejects the extracted cartridge from the side of the weapon body
Metal parts of these mechanisms can leave individualizing markings on cartridge cases

27. Moving Components
All of the moving components contact the cartridge rather than the bullet
can leave useful impressions on shotgun shell cartridges

28. Automatic
Fully automatic weapons will continue to fire & expend casings as long as the trigger is depressed and ammunition available

29. Machine & Submachine Guns
Machine guns have a heavy recoil
designed to be fired from some type of sturdy mounting
Submachine guns are designed to be fired while being held in the hands

30. Bullets When black powder was used as a propellant
projectiles had relatively low velocities
bullets were usually almost pure lead
With smokeless powders
burn rate & heat production much greater
pure lead bullets foul rifling

31. Common Types of Bullets For Rifled Firearms
Lead Alloy
lead hardened by addition of antimony
Semijacketed
have a copper-alloy or aluminum jacket that covers part of the bullet surface
usually nose is left exposed
nose configurations encourage penetration & expansion on impact
soft-point, hollow-point, bronze point, etc

32. Common Types of Bullets For Rifled Firearms
Full jacketed
consist of a lead core surrounded by a jacket of copper-nickel alloy or mild steel
usually core is left exposed at the base of the bullet
Semiautomatic pistols use full jacketed bullets
noses of bullets must slide up a ramp when rounds chambered

33. Bullet Shapes Influence aerodynamic properties
round 0r pointed noses reduce air resistance
increases striking power
some have boattailed bases
act as a rudder to reduce turbulance & decrease drag

34. Shotguns Typically characterized by their gauge
Gauge is a term which comes from the days when all firearms fired spherical lead balls
gauges were expressed as the number of appropriately-sized bullets that could be made from one pound of lead
10-gauge shotgun
10 lead balls of about the same diameter as the barrel could be made from a pound of lead

35. Cartridges Cases Made from brass Come in a variety of different shapes
may be nickel-plated to prevent corrosion
Come in a variety of different shapes
Revolvers fire straight rimmed cartridges
Self-loading pistols fire straight rimless cartridges
Can have cannelures rolled into them to prevent the bullet from being pushed back into the case

36. Cartridge Cases
Bullets may be held in place by criming or staking the mouth of the cartridge case into a cannelure on the bullet
May have nformation stamped on the head of the cartridge
identify manufacturer
identify caliber

37. Shotgun Shells Most contain pellets which come in a variety of sizes
the smaller the number, the larger the pellet
000 buckshot pellets are 0.36 inches in diameter
No. 12 birdshot pellets are 0.05 inches in diameter
The load in each shotshell depends on the gauge of the shell & the size of the pellets
12-gauge No. 1 buckshot contain 16 pellets
16-gauge no. 1 buckshot contains 12 pellets

38. Shotgun Gauge
The higher the gauge number, the smaller the diameter of the barrel
12-gauge shotgun has a bore diameter of inches
16-gauge shotgun has a bore diameter of inches
Exception
.410-gauge shotgun has a barrel inches in diameter

39. Shot gun Shells
Shotgun pellets may be made of pure lead (drop shot), lead alloy (chilled shot) or soft steel
Smaller size pellets are manufactured by pouring molten metal through a perforated plate & allowing it to fall some distance
solidifies as spheres
Larger size are made by pressing lengths of wire between cup-shaped dies

40. Bullet & Cartridge Comparisons
Impression Evidence
Bullet & Cartridge Comparisons

41. Rifling Impression Patterns

42. Bullet comparisons
Test bullet generated by firing into a water chamber or cotton box
Bullets are then examined using a comparison microscope

43. Cartridge Case Comparisions
Marks which might be found on a spent cartridge

44. Cartridge Case Comparisons
The hole in the center is the imprint from the primer pin
Striation within circle are breechblock impressions

45. Breechblock Comparison
Evidence Cartridge
Reference Cartridge

46. Breechblock Comparison
Breechblock Face
Microscopic Comparison

47. Bullet Matches

48. Extractor Matches

49. Automated Firearm Search Systems
National computerized networks have been developed to allow labs to search each other’s data
DRUGFIRE (FBI)
concentrates on cartridge markings although bullet striae can be stored as well
IBIS (Integrated Ballistic Identification System)

50. Automated Firearm Search Systems
IBIS (Integrated Ballistic Identification System)
developed by the Bureau of Alcohol Tobacco & Firearms (ATF)
incorporates two separate software programs
Bulletproof
for bullet-specific markings
Brasscatcher
for cartridge cases

51. Restoring an obliterated serial number.
Proper collection and preservation of firearm evidence.
Comparing suspect’s tool to a tool mark.
Significance of class and individual characteristics to the comparison of impressions.
Common field reagents for enhancing bloody footprints.

52. Firearms: a discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon. Not to be confused with ballistics, which is the study of a projectile in motion
Grooves: the cut or low-lying portions between the lands in a rifled
Rifling: the spiral grooves that are formed in the bore of a firearm barrel to impact a spin to the projectile when it is fired

53. Bore: the interior of a firearm
Lands: the raised portion between the grooves in a rifled bore
Caliber: the diameter of the bore of a rifled firearm. The caliber is usually expressed in hundredths of an inch or millimeters, e.g. .22 caliber and 9 mm

54. Gauge: size designation of a shotgun, originally the number of lead balls with the same diameter as the barrel that would make a pound. For example, a 12-gauge shotgun would have a bore diameter of a lead ball. 1/12 pound in weight. The only exception is the .410 shotgun, in which bore size is 0.41 inch
Breechblock: the rear part of a firearm barrel

55. Ejector: the mechanisms in a firearm that throws they cartridge or fired case from the firearm
Extractor: the mechanism in a firearm by which a cartridge of a fixed case in withdrawn from the chamber
Distance determination: the process of determining the distance between the firearm and a target usually based on the distribution of powder patte3rn or the spread of a shot pattern

56. Greiss Test: a chemical test to develop patterns of gunpowder residues around bullet holes
Choke: an interior constriction placed at or near the muzzle end of a shotgun’s barrel for the purpose of controlling shot dispersion

57. Tool Mark Comparison Examples
Matching evidence (L) and reference (R) prymarks