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Firearm ForensicsFirearms: Ballistics Ballistics - the science of the travel of a projectile in flight.The flight path of a bullet includes: travel down the barrel, paththrough the air, and path through a target.1Firearm Nomenclature: SemiautomaticFirearms Caliber - diameter of the bore; usually in 1/100 inchor mm (.22 cal or 9mm) Gauge- refers to the diameter of a shotgun barrel interms of # of lead balls it would take to weigh onepound (10 gauge, 12 gauge)SlideBarrelExtractorTrigger Firearm Identification:–––––2HammerSize and shape of bullet/caseRifling matchFiring pin/Case impression matchStriations on bullet matchSerial numbers (restoration)Safety341
Firearm NomenclatureAmmunitionBreechfaceEjectorFiring Pin ApertureExtractorCartridge (unfired)BulletGun PowderCartridge CasePrimer56Bullet cartridges A long, heavy needle would go right through the targetwithout dispersing any of its energy Spheres would be slowed down the greatest and releasemore energy, but might not get to the target72
Bullet DesignThree Main Shapes “Bullet” refers to the projectile(s) whichactually exits the barrel of the gun whenfired Bullets vary in shape and composition Most types are variations on three mainshapes and three basic compositions3
Round Nose Maximum penetration Cheapest shape to manufacture Easily loads into chambersWadCutter Used exclusively as a practice load Minimizes penetration Intended to cut target paper cleanly to facilitateeasy and accurate scoringHollow Point Spreads or mushrooms on impact Causes additional damage to target Inhibits penetrationThree Basic Compositions of Bullets Lead ½ Jacketed Jacketed (Full metal jacket)4
Basic Compositions of BulletsGun Comparisons Lead Round Nose -An elongated projectile made of a leadalloy with a rounded nose Cheap Dense but soft Easy to mold Gun barrels are a solid steel tube hollowed outby drilling. Inner tube has rifling to spin the bullet (bettertrajectory - no tumbling). ½ Jacketed- a lead bullet designed with a jacket, typicallycopper, surrounding the lower portion. Used primarily for hollow points Copper improves exit velocity Lead promotes mushrooming Jacketed (Full metal jacket) - the bullet jacket (copper)encloses the entire bullet Used to hold the shape of the bullet to maximizepenetration1718Manufacturing of Firearm BarrelsRifling Firearm barrels have grooves cut, or pressed, in the bore whichproduces RIFLING The grooves are cut in a spiral pattern Between the grooves are raised areas. These are called lands. Various rifling techniques include: broach cutting, button rifling,and hammer e)19205
Button RiflingRifling: Broach cutter Broach cutters : cutsall the groovessimultaneously byforcing cutter downbarrel and rotatingthe cutter. Button Rifling - Ahardened metal plug witha rifled cross section. It ispushed or pulled througha drilled barrel underhigh pressure. Uses nocutting but compressesmetal21Rifling: Hammer ForgingRifling Hammer Forging - A mandrelwith correct rifling is insertedinto an oversized bore and thebarrel compressed around themandrel by rolling orhammering Lands and grooves having arounded profile (Polygonal Rifling )* Association of Firearm and Tool Mark Examiners Glossary 4th Edition22 The faster the spin, the lesslikely a bullet will turnsideways and tumble. Increasing the twist of therifling to 1 in 7 will impartgreater spin than the typical 1in 12 spiral (one turn in 12inches of barrel).23246
Manufacturing of Firearm Barrels The results of rifling gives a barrel its classcharacteristicsBullets becomescarred by riflingas they traveldown the barrelof a gun Each barrel has four class characteristics1. Caliber2. Number of lands and grooves3. Direction of twist (Left or right)4. Width of lands and grooves25Class CharacteristicsGroves and Lands All class characteristicsare measurableEach class offirearm has fixedgroove-land infothat doesn't notchange Caliber Number of lands andgrooves Width of the lands andgrooves Direction of twist (left)2612327287
Bullet ComparisonComparison Microscope Impression are made on a soft bullet Since the rifling is worn away irregularly by each shot, thegrooves make a unique impression on the bullet (striations). No two rifled barrels, even those manufactured in succession,will have identical striation markings. Most important tool forfirearms examiner Two compound microscopescombined into one unit Viewer looks through theeyepiece and a field dividedinto two equal parts isobserved Bullet comparisons- requiresreflective light 29Comparison Microscope30Bullet Comparison Obtain sample bullet. Fire similar bullet from suspect gun (into watercotton-filled tank or ballistics gel).Split-imagecomparison of firingpin31328
StriationsBullet Comparison Striations form the individual characteristics of thebarrel. The first step incomparing firedbullets is examiningthe land and groovewidth These bullets havedifferent land andgroove width333435369
Cartridge CasesCartridge Case Comparisons Pulling trigger releases the firing pin that then strikesthe primer and ignites the powder. The bullet case is propelled backwards (as the bulletmoves forward) and is imprinted by the breechblock(back of barrel). The shape of the firing pin will be impressed into therelatively soft metal of the primer on the cartridgecase. Spent case extractors also leave identifiable marks. Areas of comparison– Breech face marks– Firing Pin impressions– Extractor marks– Ejector marks– Chamber marks37Computerized ImagingGunpowder Residues Make it possible to store bullet and cartridge surfacecharacteristics National Integrated Ballistics Information Network (NIBIN)produces database files from bullets and cartridge casingsretrieved from crime scenes or test fires from retrievedfirearms, often linking a specific weapon to multiple crimes. Final comparison will be determined by the forensicexaminer through traditional microscopic methods. The firing pin of a firearm strikes the primer of a cartridge. Gunpowder in the cartridge case burns, causing it to changefrom a solid material to a gas creating pressure. When the bullet exits the muzzle, pressure behind it blows thegunshot residues out of the firearm's barrel under highvelocity. Used to link multiple crimes to a single weapon.Visible gunshotresidues aroundbullet entrance hole.394010
Tests done:Gunpowder ResiduesExamine microscopically for presence of gunpowderresidue Sodium rhodizoante test (lead) Greiss test – presence of Nitrates Firing a weapon does not fully consume all thegunpowder Unburned and partially burned propellant withsmoke are emitted. Can be used to determine firing distance (if smoke,etc. is on victim, pattern of residue deposition, etc.). Chemical analysis ofresidues.Gunpowderparticulate residuearound bulletentrance hole.4142GRIESS TESTSODIUM RHODIZONATE TESTTests for the presence of nitrites. Converts nitrites to nitrates. Tests for the presence of lead. Converts lead to lead rhodizonate. 434411
Gunpowder Residues (GSR)Gunpowder ResiduesSoot is seen on the hand of a suicide victim, giving an indicationthat he was holding the weapon when it was fired.Scanning ElectronMicrograph of GSRDiagram of the SEM pattern of GSRMost primers containlead, antimony andbarium containingcompounds.45Serial Number Restoration Many manufactured items made of metal have serialnumbers stamped in them for 46Serial Number Restoration Scratched out serialnumbers can be restoredsince stamping marks onmetal deforms layers deepinto the metal structure. Apply etching agent toshow original numbers. Magnaflux method: Usesmagnetic properties (ironor steel) – non destructive4812
4950Tool MarksDefined as any impression, cut, gouge, or abrasioncaused by a tool coming into contact with anotherobject Typical features (classcharacteristics) Cuts, tears, gouges orother wear marks areused to individualize thetool.Rubberhoses cutby thesameknife515213
Tool Marks: Preserving EvidenceUNDER NO CIRCUMSTANCESHOULD THE CRIME SCENE INVESTIGATORATTEMPT TO FIT THE SUSPECT TOOL INTOTHE TOOL MARKSiliconecastingmaterialSi Cast53Other Impression Evidence54Other Impression Evidence Footprints Bitemarks Tire/wheel tracks Footprints555614
FootprintsFootprints57Dental/Bite Marks58Dental/Bite Marks Dental Impression of gum,food, vicitms, etc. At Left: A. Chewing gumfound at crime scene. B.dental impressions ofvictim and suspect.Unique root canal work ofsuspect found on gum.59Ted Bundy Ted Bundy picked up for murder two sororitywomen at FSU using fake name and ID. One victim had bite marks on buttock. Casting of Bundy’s teeth taken (forcibly). Found tooverlay (match) exactly the bite wound. Defended himself but convicted and sentenced todeath. Before execution admitted to more than 40 othermurders (but gave no info or details).6015
Firearm Forensics 1 Firearms: Ballistics Ballistics - the science of the travel of a projectile in flight. The flight path of a bullet includes: travel down the barrel, path through the air, and path through a target.
