Intrductin Ballistic evidence helps explain: What type f firearm was used The caliber f the bullet The number f bullets fired Where the shter was lcated Whether a weapn was fired recently If a firearm was used in previus crimes 1 Frensic Science: Fundamentals & Investigatins, Chapter 17
Vcabulary Ballistics is the study f bullets and firearms. A firearm is a weapn, such as a gun, capable f firing a prjectile using a cnfined explsive. Gunpwder is ptassium nitrate, charcal, and sulfur. When ignited, it expands t 6 times its riginal size, causing a vilent explsin. 2 Frensic Science: Fundamentals & Investigatins, Chapter 17
Bullet pinted prjectile cmpsed f lead, cpper, r cmbinatin f varius metals. Can be metal-jacketed, hallw-pinted, r even plastic cated. Primer pwer mixture initiates the cntained explsin that pushes the bullet dwn the barrel. Struck by firing pin. Firing pin strikes the cartridge casing and leaves an impressin. 3 Frensic Science: Fundamentals & Investigatins, Chapter 17
Anvil and flash hle prvide the mechanism f delivery the explsive charge frm the primer pwer t the gunpwder. Headstamp n bttm f cartridge casing identifies the caliber and manufacturer f bullet. 4 Frensic Science: Fundamentals & Investigatins, Chapter 17
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Histry f Gunpwder and Firearms 8 Chinese invented gunpwder ver a thusand years ag (ptassium nitrate, charcal, and sulfur. Muzzle-lading matchlcks used wicks t ignite the gunpwder Muzzle-lading gunpwder and prjectile laded dwn the firearm s barrel (muzzle) Flintlck weapns, which used sparks frm a chip f flint instead f wicks t ignite gun pwer. Can be used in damp weather. Frensic Science: Fundamentals & Investigatins, Chapter 17
Histry cntinued 9 Percussin firing Cartridge and breech lading Cartridge case that hlds a bullet The Percussin rifle was a type f rifle (r musket ) that utilized the percussin lck (r caplck) mechanism t fire a bullet r musket ball. The Percussin lck mechanism was an evlutin f the Flintlck mechanism used n earlier muskets and rifles, with the Percussin rifle being intrduced frm arund 1820. Frensic Science: Fundamentals & Investigatins, Chapter 17
Breech - ppsite end f barrel A breech-lading weapn is a firearm in which the cartridge r shell is inserted r laded int a chamber integral t the rear prtin f a barrel. Revlver, semi-autmatic, and autmatic handguns 10 Frensic Science: Fundamentals & Investigatins, Chapter 17
Mdern firearms divided int Lng Guns and Handguns 11 Lng guns (require use f tw hands fr accuracy) Rifles fire bullets Shtguns fire pellets (sht) r a single prjectile (slug) Handguns Pistls are fired with ne hand Revlvers have a cylinder that hlds usually six cartridges and fire in rapid successin. Fully Autmatic and Semi-autmatic hlds 10 cartridges, but fires nly ne bullet per pull f trigger.
Autmatic fires repeatedly as lng as the trigger is pressed. Semi-autmatic hlds 10 cartridges called a magazine r clip, but fires nly ne bullet per pull f trigger. Bth the empty cartridge ejects and the next cartridge advances autmatically. 12 Frensic Science: Fundamentals & Investigatins, Chapter 17
Firearms and Rifling Wrd Rifle riginally referred t the grves in indentatins in the rifle s barrel. 13 Grves and ridges (lands) in the barrel f a gun prduce the twisting that adds accuracy This leaves a rifling pattern n the bullet that is unique fr each gun. Therefre, a bullet can be matched t the specific gun frm which is was fired Frensic Science: Fundamentals & Investigatins, Chapter 17
Bullets, Cartridges, and Calibers A significant part f ballistics invlves examining used bullets and their spent cartridge casing fr telltale markings left n them by the firearm that sht them. 14 Cartridge a case that hlds a bullet, primer pwder, and gunpwder The bullet, usually f metal, is ut frnt with the cartridge, hlding the primer and prpellant pwders, behind. Bullets are named by their caliber and length, Smetimes a cartridge is incrrectly referred t as a bullet Frensic Science: Fundamentals & Investigatins, Chapter 17
Hw a Firearm Wrks 1. The firing pin hits the base f the cartridge, igniting the primer pwder 15 2. The primer pwder sparks thrugh the flash hle t the main prpellant supply Frensic Science: Fundamentals & Investigatins, Chapter 17
Hw a Firearm Wrks 3. The pressure f the explsin pushes the bullet frm the casing int the barrel 16 4. The bullet fllws the lands and grves spiraling ut f the barrel Frensic Science: Fundamentals & Investigatins, Chapter 17
Caliber f the Cartridge Caliber a measure f the diameter f the cartridge In hundredths f an inch Cmmn calibers include.22,.25,.357,.38,.44, and.45 Why shuld the caliber f ammunitin match the firearm that shts it? If they d nt match, what culd g wrng? 17 Frensic Science: Fundamentals & Investigatins, Chapter 17
Naming f Bullets and Cartridges Bullets and cartridges are named basis the diameter f the bullet and the length f the cartridge frm base t case rim. 18 Frensic Science: Fundamentals & Investigatins, Chapter 17
The Study f Bullets and Cartridge Casings 1. As a gun is fired, the barrel marks each bullet with its wn unique pattern f lands and grves. 2. Investigatrs match bullet t the gun it was fired. 3. Spent cartridge casings frm crime scene with bullets and spent cartridges sht frm suspected firearms are cmpared. 19
T get a knwn bullet fr cmparisn, investigatrs test-fire the weapn int a water tank r gel blck. This captures the bullet withut damaging it. Then they can cmpare the markings n knwn bullets with thse n the suspect bullets. 20 Frensic Science: Fundamentals & Investigatins, Chapter 17
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22 Marks n the Spent Cartridge Casings Firing pin marks appear n the bttm rim r center f the spent cartridge can be used t match a cartridge t a firearm Breechblck marks prduced when the cartridge casing slams backward and strikes the breechblck Extractr marks minute scratches prduced as the cartridge is placed in firing chamber. Ejectr marks when cartridge is remved frm chamber.
Natinal Data Bases Search all registered firearms. 23 Frensic Science: Fundamentals & Investigatins, Chapter 17
Gunsht Residues 24 Gunsht Residues (GSR) Particles f unburned pwder (nitrates) and traces f smke Leave traces n the hand, arm, face, hair, r clthing f the shter and/r victim Chemical testing can detect residue even if remval is attempted Distance frm victim t shter can be determined by examining the residue pattern n the victim. GSR decreases as distance between firearm and victim increases.
Trajectry path f the prpelled bullet. Tw reference pints are needed t define the trajectry Investigatrs can figure the shter discharged the firearm smewhere alng that line 25 Frensic Science: Fundamentals & Investigatins, Chapter 17
Trajectry Reference pints can be bullet hles in bjects r victims An entry pint and exit pint n a victim Gunsht residue r spent cartridge casings Lasers can trace a straight-line path t determine the psitin f the shter 26 Frensic Science: Fundamentals & Investigatins, Chapter 17
Trajectry and Gravity Bullet s path is slightly curved Gravity pulls it dwnward as the bullet mves frward 27 Frensic Science: Fundamentals & Investigatins, Chapter 17 Diagram is highly exaggerated
Determining the Lcatin f the Shter Building is 60 feet away alng the hrizn line Bullet hle is 4 feet abve the grund Where is the shter lcated? 28 Frensic Science: Fundamentals & Investigatins, Chapter 17
Triangulatin B is where the shter is lcated; find the length f BC The Abc triangle has the same prprtins as the ABC triangle Ab Ac AB AC S r AB = 732.3 23.9" 23.5" AB 720" 29 Frensic Science: Fundamentals & Investigatins, Chapter 17
Triangulatin 30 Using Pythagrean s therem AB 2 = AC 2 + BC 2 732.3 2 = 720 2 + BC 2 BC 2 = 732.3 2 720 2 BC 2 = 536117 518400 BC = 17717 (square rt) BC = 133.1 inches BC = 11.1 feet Frensic Science: Fundamentals & Investigatins, Chapter 17 We knw that the bullet hle in the seat is fur feet abve the grund, s the shter is 15.1 feet abve the grund
Bullet Wunds investigated t cnfirm r dispute witness s stry. 1. Entrance wunds are smaller than exit because the skin is smewhat elastic and it stretches when a bullet enters the bdy. S wund is smaller than bullet. 2. Exit wunds are larger because the bullet mves thrugh the bdy, it may cllect and carry bdy tissue and bne with it. 3. When a bullet penetrates clthing first, fibers may be embedded in the wund. 4. Gunsht residue usually fund at entrance wunds. 31 Frensic Science: Fundamentals & Investigatins, Chapter 17
1. If the gun is fired with the muzzle tuching the victim s skin, ht gases released frm the muzzle flash may burn the skin, leaving a telltale mark. High-speed bullets are mre likely t pass thrugh a bdy than lw-velcity bullets. Small-caliber bullets, (.22,.25 etc) tend t ldge within the bdy, while large-caliber bullets will pass thrugh. 32 Frensic Science: Fundamentals & Investigatins, Chapter 17
............. Summary.... Ballistics is the study f bullets and firearms. Firearms are divided int tw grups lng guns and hand guns. Fired bullets shw patterns f lands and grves that match the rifling pattern in the barrel. A cartridge cnsists f primer pwder, gunpwder, a bullet and the casing material. The caliber f a cartridge usually is a measure f its diameter. 33 Frensic Science: Fundamentals & Investigatins, Chapter 17
................. Summary Investigatrs als check fr firing pin, breechblck, extractr, and ejectr marks. Gunsht residue can help recreate a crime. Using at least tw reference pints, an investigatr can recreate a bullets trajectry and determine where the shter was lcated. Examining bdy wunds can determine where a bullet entered and exited the victim. 34 Frensic Science: Fundamentals & Investigatins, Chapter 17