2 The vast majority of U.S. homicides involve guns. And they are more powerful than ever.Lansing State Journal, July 20071998--Deaths due to handguns US 11,789 Germany 373 Canada 151 Australia 57 England and Wales 54 Japan 19 In 2004 there were 29,569 gun deaths 56 percent suicides 40 homicide
3 Introduction Ballistics- is the study of bullets and firearms Firearm = a weapon, such as a gun, capable of firing a projectile using a confined explosiveQuestions that can be answered by analysis of ballistic evidenceWhat 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?
4 History of Gun Powder and Firearms Gunpowder invented over 1,000 yrs ago by chineseGunpowder is a mixture of potassium nitrate (saltpeter), charcoal, an sulfurWhen ignited gunpowder expands to six times its original size causing a violent explosionMatchlock –used wicks to ignite the gunpowderFlintlockMuzzle (barrel) LoadersGunpowder and projectile packed down barrelBarrel = the long, metal tube thatguides a projectile out of thefirearmMuzzle = end of the barrel of aPercussionCartridge and bullet
5 Long Guns and Handguns Long Guns Handguns Rifles- fire bullets Shotguns- fire either small round pellets (shot) or a single projectile called a sluggauge = the number of lead balls matching the barrels diameter that it takes to weigh one poundHandgunsPistols- handguns that can be fired with one handSingle shot initiallynot as powerful and/or accurate as riflesToday, can be classified as revolvers or semiautomaticsRevolvers- have a cylinder which contains several cartridges that can be fired in rapid successionInvented by Samuel Colt, patented in 1835Cylinder can hold several cartridgesSemiautomaticHold 10 cartridges in one magazine (clip)Fire one bullet per pull of triggerThe empty cartridge ejects and the next cartridge advances automaticallyFully automaticFire repeatedly as long as trigger is pressed
6 Firearms and RiflingAn archer will hit a target with greater accuracy if there is a twist on the end of the arrow feathersSame applies to guns and bulletsBarrel has lands and groovesRifling = spiral pattern of lands and grooves in the barrel of a firearmLands = raised areaGrooves = indentationsLands and grooves cause bullet to spiral like a footballThe “rifling pattern” left on the bullet is specific to each firearmNo two guns, even of same model, are rifled the same when madeProvides individual evidence
7 Anatomy of a CartridgeCartridge = a case that holds a bullet, primer powder, and gunpowderShell Casing = the metal (usually brass) housing from the gunpower of a firearmThe bullet can be composed of lead copper, or a combination of various metalsLeadLead alloy (lead mixed w/ other metalsSemijacketed- thin layer of brass coatingFully jacketed-jacketed-completely covered with brassGreater penetration powerThe primer powder mixture initiates the contained explosion that pushes the bullet down the barrelStruck by firing pin of firearm, pressure caused ignitionThe anvil and flash hole provide the mechanism of delivering the explosive charge from the primer powder to the gunpowderThe headstamp on the bottom of the cartridge case identifies the caliber and manufacturer
8 How a Firearm WorksPull the trigger and the firing pin of the firearm hits the base of the cartridge, igniting the primer powder mixtureThe tiny explosion (not much more than a spark) of the primer powder misture on the anvil delivers a spark through the flash hole to the main gunpowder suppyThe main gunpowder supply ignites, and the pressure of the explosion pushes the bullet from the casing and into the barrel of the firearm. The amount of gunpowder and mass of bullet determines the speed of the bulletThe bullet follows the lands and grooves pattern of the barrel and begins to spiral before it leaves the barrel
9 Caliber of the Cartridge Caliber- a measure of the inside diameter of a firearm barrelBullets (and their cartridges) are name by caliber and length.The caliber is a measure of the diameter of the cartridge.22, .25, .357, .44, and .45 are common calibersExample .45 = 45/100 of an inchEuropean method using metric system (example 9mm)Bullet removed from wound or crime scene can be linked to a gun by its caliber size
10 Marking on BulletsLands and grooves rifling pattern in barrel of gun leaves a unique pattern on bulletsuspected weapons can be test fired and bullets compared for individualizing evidence
11 Marks on a Spent Cartridge Marks left on bottom of cartridge by firing pins, can be analyzedBreechblock marks are produced on cartridge as it travels in opposite direction of bulletBreech is the rear part of a firearm barrelWhere cartridge is loaded, opposite muzzleCartridge hits breech block and mark is leftsuspected weapons can be test fired and cartridges compared for individualizing evidenceSome other marksExtractor and Ejector marksExtractor – mechanism that places cartridge into chamber of firearmEjector – mechanism that removes cartridge from chamber after firearm has fired
12 Gunshot ResiduesAll firearms explode gunpowder and produce gunshot residue (GSR)Residues are traces of smoke and particles of unburned powder carried sideways from the firearm by the expansion of gases as the bullet is firedGunshot residues contain nitrates and metalsResidues stick to the person holding the firearm and leave evidence on the shooterThe amount of GSR on the victim decreases as the distance between shooter and victim increases
13 Trajectory Trajectory is the path of the for the propelled bullet Used to determine the position of a shooterTrajectory can be calculated by finding two or more referenceIf ignoring gravity, it can be assumed that projectiles such as bullets travel in straight linesReference points can bebullet holes in objects or victimsAn entry point and exit point on a victimGunshot residue or spent cartridge casingsLasers can trace a straight-line path to determine the position of the shooter
14 Gravity and Trajectory Two major forces acting on a bullet after it has been firedForward force of the gunshot andDownward force of gravityIf shot from close to medium distances gravity can be negated in calculation of trajectoryGravity needs to be accounted for if shots are fired from greater distances
15 Determining Location of Shooter Building is 60 feet away along the horizon lineBullet hole is 4 feet above the groundWhere is the shooter located?
16 Triangulation B is where the shooter is located; find the length of BC The Abc triangle has the same proportions as the ABC triangleSo orAB = 732.3”
17 Triangulation Using Pythagorean’s theorem AB2 = AC2 + BC2 BC = √17717 (square root)BC = inchesBC = 11.1 feetWe know that the bullet hole in the seat is four feet above the ground, so the shooter is 15.1 feet above the ground
18 Sample 1 Ab = 32” Ac = 24 “ CALCULATE BC Building is 40 feet away along the horizon lineBullet hole is 4 feet above the ground
19 Sample 2 Ab = 22” Ac = 14“ Calculate BC Building is 20 feet away along the horizon lineBullet hole is 4 feet above the ground
20 Bullet WoundsWhy do entrance wounds tend to be smaller than exit wounds? Bullet enters body small May pick bone and tissue as it travels through body tumbling effect If the bullet penetrates clothing, what can fibers embedded in the wound indicate? entrance vs exit wound Where is gunshot residue usually found? usually only around entrance wounds If the gun is fired with the muzzle touching the victim’s skin, what telltale mark may show up? burn mark on skin Will larger or will smaller caliber bullets tend to lodge within the body rather than passing through? Why? smaller caliber-less velocity (speed)
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