1. Forensics: Ballistics

2. Vocabulary
Ballistics – the study of projectiles (bullets) and firearms
Barrel – the long, metal tube that guides a projectile out of a firearm
Bullet – the projectile that is released when a firearm is discharged
Caliber – a measure of the inside diameter of a firearm barrel
Cartridge – a case that holds a bullet, primer powder, and gunpowder

3. Vocabulary
Firearm – a weapon capable of firing a projectile using a confined explosive as a propellant
Fully automatic – a firearm with a clip-fed mechanism that fires repeatedly as long as the trigger is pressed
Gunshot residue (GSR) – the tiny particles expelled from a firearm when it is fired
Lands and Grooves – the ridges (lands) and the depressions (grooves) found on the inside of a firearm’s barrel that are created when the firearm is manufactured

4. Vocabulary
Muzzle – the end of the barrel from which the projectile exits a firearm
Pistol – a handheld firearm
Revolver – a pistol with a revolving cylinder
Rifle – a firearm that has a long barrel; a long gun
Rifling – the spiral pattern of lands and grooves in the barrel of a firearm

5. Vocabulary
Semiautomatic – a pistol with a clip-fed mechanism that fires one shot per pull of the trigger; the empty cartridge ejects and the next cartridge advances automatically
Shell casing – the metal (usually brass) housing for the gunpowder of a firearm
Trajectory – the path of flight of a projectile

6. What we will learn
The differences between a handgun, a rifle, and a shotgun
Distinguishing between a bullet and cartridge
The rifling on the gun barrel and how it affects the flight of a projectile
Relationship between barrel size and caliber
How bullets are test-fired and matched
Role of ballistics recovery and examination at the crime scene
Position of the shooter based on bullet trajectory

7. What questions does ballistics help answer at a crime scene?
What type of firearm was used?
What was the caliber of the bullet?
How many bullets were fired?
Where was the shooter standing?
What was the angle of impact?
Has this firearm been used in a previous crime?

8. History of Firearms Chinese invented gunpowder
Potassium nitrate, charcoal, and sulfur
Expands to 6 times original size
14th century – directed explosives down a cylinder and move a deadly projectile
Matchlock weapons
Flintlock weapons
Muzzle-loaders
Breech-loaders

9. Firearms in Forensics
1835 – London, England. Mold mark used to make bullet from molten lead used as evidence in homicide case
1863 – Examination of the bullet type and design used to shoot Gen. Stonewall Jackson showed he was shot by one of his own men
1879 – Minnesota. Rifling marks from a revolver used in court to differentiate two revolvers
1925 – The comparison microscope is developed by Philip Gravelle

10. Modern Firearms Two basic Types
Long guns – use of two hands for accurate firing
Handguns – fired with one hand (pistols)

11. Firearms Continued Rifles – fire cartridges
Long Guns
Rifles – fire cartridges
Shotguns – fire small round pellets (shot) or single projectile called slug

12. Handguns
Revolver – cylinder that holds cartridges turns as it fires
Usually Holds up to 6 cartridges in the cylinder
Semiautomatic – fire only one bullet per pull of trigger
Holds up to 20 cartridges in a clip (magazine)
Fully Automatic – fire repeatedly as long as trigger is pressed

13. Rifling
Lands and grooves cause bullet to spiral when exiting the barrel
Impossible to produce two identically rifled gun barrels
Barrel marks each bullet with own specific pattern

15. How lands and grooves are made

16. Bullets and Cartridges
Anatomy of a Cartridge
Bullet – made of lead, copper, or combination
Can be metal-jacketed, hollow-pointed, plastic-coated
Primer powder – initiates explosion that pushes bullet down barrel
Anvil and Flash Hole – deliver the explosive charge from primer powder to gun powder
Headstamp – on bottom of cartridge casing identifies caliber and manufacturer

18. How a Firearm Works
Pull the trigger – firing pin hits base of cartridge & ignites primer powder mixture
Tiny explosion of primer powder on anvil shoots spark through flash hole to gunpowder supply
Gunpowder ignites & pressure of explosion pushes bullet from casing into barrel of firearm.
Bullet follows lands and grooves pattern of barrel and spirals before leaving the barrel

19. Caliber of the Cartridge
Named by caliber and length
Common calibers: .22,.25,.357,.38,.44,.45
Usually measured in hundredths of an inch
.45 caliber – 45/100 of an inch
European method – metric system (mm)
Caliber also refers to diameter of a barrel
Caliber of ammunition should match caliber of firearm that shoots it

20. Bullets and Cartridge Casings at Crime Scenes
Investigators compare bullets and spent cartridges from crime scene with bullets and spent cartridges from suspected weapon
Test-fire weapon into water tank or gel block to capture bullet without damaging it
Compared using comparison microscope

23. Marks on Spent Cartridge Casings
Firing pin marks are left on spent cartridge
Also individual to each gun
Left on cartridge when firing pin strikes bottom of cartridge when firearm is shot
Other markings:
Breech marks
Extractor markers
Ejector marks
*** extractor and ejector do not happen in revolver

24. Class vs. Individual Characteristics
What is a class characteristic?
The properties that all the members of a certain group of objects or substances have in common
What is an individual characteristic?
Properties of evidence that can be attributed to a common source with extremely high degree of certainty

25. Class vs. Individual Characteristics of Firearms
Type of gun (long gun, handgun, rifle, shotgun, pistol, revolver)
Manufacturer (Beretta, Smith & Wesson, Winchester)
Caliber
Individual:
Rifling (lands and grooves)
Spent casing markings
Firing pin marks

26. Gunshot Residue (GSR)
Traces of smoke and particles of unburned powder carried sideways from firearm by expansion of gases as bullet is fired
Contain nitrates – stick to shooter and area fired
Amount found decreases as distance between firearm and victim increases
GSR looked for to recreate crime scene and find suspect.

28. Databases
Can be searched to match crime-scene evidence to registered weapons
NIBIS (National Integrated Bullet Identification System) – computer files of ballistic markings used in previous crimes
Drugfire – FBI database focuses on cartridge casings
2002 – merged to form NIBIN (National Integrated Ballistics Network)

29. Trajectory
Helps to determine where the shooter was located during a crime
Calculating trajectory – two reference points along the flight path of projectile are used to assume that a shooter discharged firearm somewhere along that line
** ignoring gravity

30. Calculating Trajectory
Reference points – bullet holes in an object or bullet wound on a victim
Less specific reference points – GSR on objects, spent cartridge casings.
Victim’s body – entrance wound and exit wound
Tools such as lasers and repositioning corpse to position at time of impact are helpful
**Exceptions** - bullets can ricochet, become damaged and not provide direct path

32. Gravity and Trajectory
Two major forces act on bullet once fired:
Forward force of gunshot
Downward force of gravity
Bullet begins to drop as soon as shot
farther the shooter – greater the effect
Wind speed and direction also effect shooter angle

33. Determining the Location of a Shooter
Scenario: Bullet is found in upholstery of car’s front driver’s seat. Bullet hole is found in front driver side window.
Shot seems to have come from a window in some apartments across the street.
What are the two reference points to predict a path of trajectory?
bullet in seat, hole in window
Police use a laser to project path

34. Wind shield Path of bullet building Horizon Distance along path of
bullet to window, 23.9”
Distance along
horizon to
window, 23.5” y x
60 feet
building

35. Calculation Which window? Formula:
Distance from car to building: 60 feet or 720”
Distance from window to car seat (along horizon): 23.5”
Distance from window to car seat (along bullet path): 23.9”
Formula:
Distance to window along bullet path = distance to shooter (x)
Distance to window along horizon distance to building

36. Bullet Wounds
Entrance wounds – generally smaller because skin is elastic
Exit wounds – bigger because bullet may pick up tissue, bone, etc as it goes through body
Clues near body:
If bullet penetrates clothing first, fibers may be imbedded into wound in direction of penetration
GSR – found around entrance wounds
If in contact with skin, hot gases may burn skin

37. Bullet wounds Fate of a bullet in body:
May ricochet off bone and do internal damage before exiting
May not exit the body at all

38. Factors that influence fate:
High speed – may pass directly through
Much more likely than low velocity
Small caliber bullets – more likely to be lodged
Larger caliber bullets – likely to pass right through