Presentation on theme: "Ballistics the study of projectiles (bullets) and firearms."— Presentation transcript:
Ballistics the study of projectiles (bullets) and firearms
FAQs in Forensic Ballistic examinations: 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?
History Over 1000 years ago: Chinese invented gunpowder (composed of KNO3, charcoal and sulfur). When ignited, it expands to 6X its original size, causing a violent explosion.
14th century in Europe: inventors learned that they could direct the explosive force of gunpowder down a cylinder to move a deadly projectile Muzzle-Loader weapons = gunpowder and projectile were loaded down the muzzle (firearms barrel) Matchlock gun = the earliest firearm in which wicks carried a flame to the gunpowder. Flintlock = replaced matchlock; used sparks from a chip of flint instead of wicks to ignite the powder. (allowed them to work even in damp weather).
1500s: introduction of cartridge (a case that holds a bullet, primer powder and gunpowder). Percussion firing = replaced the flintlock. A hammer hits the primer powder (which exploded) igniting the gunpowder. Cartridges are loaded into the gun from the opposite end of the barrel (the breech). Can be loaded more quickly and more effective in shooting in the desired direction.
2 Basic types of modern firearms: 1) Long guns – rifles and shotguns; requires the use of 2 hands for accurate firing. Rifles – fire bullets Shotguns – can fire either small round pellets (shot) or a single projectile (slug) 2) Handguns/pistols – fired with 1 hand. Revolvers – holds 6 cartridges in the cylinder Semi-automatic – permits the loading of up to 10 cartridges into a magazine (clip) which is locked into the grip of the firearm.
Difference between semiautomatic and fully automatic weapons: They both eject the empty cartridge and advance the next cartridge. Semiautomatic fire only 1 bullet per pull of the trigger. Fully automatic weapons fire repeatedly as long as the trigger is pressed.
Rifling = the spiral patterns of lands and grooves in the barrel of a firearm Lands and grooves = the ridges (lands) and depressions (grooves) found on the inside of a firearms barrel that are created during manufacturing. Causes the bullet to spiral when exiting the barrel of the gun.
EACH GUN HAS ITS OWN UNIQUE PATTERN. A bullet can be matched to the specific gun from which it was fired. A bullet can be matched to the specific gun from which it was fired.
Anatomy of a cartridge: The bullet (the projectile) can be composed of Pb, Cu or combinations of various metals. It can be metal-jacketed, hollow-pointed, or even plastic-coated. The primer powder mixture – initiates the contained explosion that pushes the bullet down the barrel. The pressure causes the powder to ignite. The firearms firing pin may strike the bottom of the cartridge casing in the centerfire cartridge, or it might strike anywhere on the rim of the rimfire cartridge.
The anvil and flash hole provide the mechanism of delivering the explosive charge from the primer powder to the gunpowder. The headstamp on the bottom of the cartridge casing identifies the caliber and manufacturer.
Bullets and their cartridges are named by caliber and length. Caliber = a measure of the diameter of the cartridge. Common calibers: (usually measured in hundredth of an inch) (35.7/100 inch, or 357/1000 inch) (45/100 inch = almost half and inch) The European calibers: (uses the metric system) 9mm
Examiners compare the barrel marks on each unknown bullet and cartridge casings with the lands and grooves of the known bullets and cartridge casings (fired from a suspected gun) side-by-side, on a comparison microscope. The weapons are test-fired into a water tank to capture the bullets without damaging it.
Marks used for identification and comparisons: Firing pin marks left on the cartridge cases as it strikes the cartridge can also be used to identify a firearm. Breechblock markings left on spent cartridge case as it hits the breechblock to prevent the cartridge from hitting the user as it recoils. Markings are unique to the firearm.
Extractor and ejector marks (minute scratches) produced as the cartridge is placed in the firing chamber (by the extractor) and removed from the chamber after firing (by the ejector). Only produced in semiautomatic and fully automatic weapons. (In revolvers, there are no extractor or ejector; cartridges are hand-fed and manually removed).