Forensic Firearm Identification www.precisionforensictesting.com
History of Forensic Firearm Identification 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
Different Types of Firearms Semiautomatic Pistol A repeating firearm requiring a separate pull of the trigger for each shot fired, and which uses the energy of discharge to perform a portion of the operating or firing cycle* Revolver A firearm with a cylinder having several chambers so arranged as to rotate around an axis and be discharged successively by the same firing mechanism.* Double Action - A mechanism in which a single pull of the trigger cocks and release the hammer.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Different Types of Firearms Revolver Single Action - An action requiring the manual cocking of the hammer before sufficient pressure on the trigger releases the firing mechanism.* Bolt Action Rifle A firearm that is manually loaded by the reciprocation and engagement of a bolt * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Different Types of Firearms Lever Action A design wherein the breech mechanism is cycled by an external lever generally below the receiver.* Slide Action An action which features a movable forearm which is manually actuated in motion parallel to the barrel by the shooter. Also known as PUMP ACTION.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Firearm Nomenclature Slide Barrel Extractor Trigger Hammer Safety
Firearm Nomenclature Breechface Ejector Firing Pin Aperture Extractor
Firearm Nomenclature Cylinder Trigger Hammer Barrel Breechface Firing Pin
Centerfire Ammunition Cartridge (unfired) Bullet Gun Powder Cartridge Case Primer
Shotgun Ammunition Shotshell - A cartridge containing projectile(s) designed to be fired in a shotgun. The cartridge body may be metal, plastic or paper.* Shot Typically lead or steel Wadding Plastic cup which holds the shot * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Rifle Ammunition Bottleneck Cartridge - A cartridge case having a main diameter and a distinct angular shoulder stepping down to a smaller diameter at the neck position of the case.* Typically associated with rifle ammunition. * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Rimfire Ammunition Rimfire is a type of ammunition which has the priming compound around the circumference of the base.
Ammunition Headstamp - Numerals, letters and symbols (or combination thereof) stamped into the head of a cartridge case or shotshell to identify the manufacturer, caliber, gauge or give additional information.* * Association of Firearm and Tool Mark Examiners Glossary 4 th Edition
Types of Bullets Full Metal Jacket A projectile in which the bullet jacket encloses the entire bullet, with the usual exception of the base.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Jacketed Soft Point Cannelure - A circumferential groove generally of a knurled or plain appearance in a bullet or cartridge case.* Typically found on revolver and rifle bullets Types of Bullets A bullet designed with the soft lead core exposed at the nose. * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Types of Bullets Jacketed Hollow Point A bullet designed with a jacket, typically copper, surrounding the lower portion. The nose of the bullet has a hollow point.
Types of Bullets Lead Round Nose An elongated projectile made of a lead alloy with a rounded nose.
Types of Bullets Semi-wadcutter A bullet designed with a truncated nose and sharp shoulder
Types of Bullets Wadcutter A cylindrical bullet design having a sharp shouldered nose intended to cut target paper cleanly to facilitate easy and accurate scoring.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Boat Tail Types of Bullets A specific design of bullet having a tapered or a truncated conical base.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Bullets Bullets come in different shapes, sizes, and profiles. When bullets hit objects they can break apart or become deformed
Manufacturing of Firearms All surfaces of firearms are machined during the manufacturing process The machining process leaves marks which are specific to that particular method These marks can be rough enough to be seen with the naked eye or may be smoother, requiring the aid of a microscope
Manufacturing of Firearms Flat surfaces of firearm parts are machined on a milling machine The cutting tool of the milling machine is called the endmill
Manufacturing of Firearms Endmills can cut with either their side or the end When endmills cut using the end, the resulting surface has circular or arch marks
Manufacturing of Firearms Round parts are machined with a lathe
Manufacturing of Firearm Barrels Firearm barrels have grooves cut, or pressed, in the bore which produces RIFLING These 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 forging
Manufacturing of Firearm Barrels Broach Rifling - A tool having a series of cutting edges of slightly increasing height used to cut the spiral grooves in a barrel. All grooves are cut with a single pass of the broach.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Manufacturing of Firearm Barrels Button Rifling - A hardened metal plug with a rifled cross section configuration. It is pushed or pulled through a drilled and reamed barrel so as to cold form the spiral grooves to the desired depth and twist.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Manufacturing of Firearm Barrels Hammer Forging - An internal mandrel with rifling configuration which forms rifling in the barrel by means of external hammering.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Cut Rifling - Rifling made by a broach cutter or button with produce rifling with sharp edges Types of Rifling
Polygonal Rifling - Lands and grooves having a rounded profile. This type of rifling is produced with Hammer Forging Types of Rifling
Manufacturing of Firearm Barrels The results of rifling gives a barrel its class characteristics Measurable features of a specimen which indicate a restricted group source. They result from design factors, and are therefore determined prior to manufacture.* * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Manufacturing of Firearm Barrels Each barrel has four class characteristics 1. Caliber (bore diameter:.357,.22,.45) 2. Number of lands and grooves 3. Direction of twist 4. Width of the lands and grooves
All class characteristics are measurable Caliber Class Characteristics Number of lands and grooves Width of the lands and grooves Direction of twist 1 2 3
Theory of Firearm Identification The surfaces of firearms are machined. Marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. They are unique to that tool and distinguish it from all other tools.* Bullets and cartridge cases can be compared using marks left on them through their contact with a firearm. * Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Functioning of a Firearm Video compliments of www.firearmsid.com and Hi-Point firearms
Comparison Microscope Allows viewing of two items simultaneously Magnification is typically adjustable from 4X to 40X magnification
Bullet Comparison When firearms are used in crimes, quite often bullets are recovered from crime scenes or at autopsy Markings left on bullets by the machining process and cutting of the rifling in the barrel are called striations and are used for comparison
Bullet Comparison The first step in comparing fired bullets is examining the land and groove width These bullets have different land and groove width
Bullet Comparison Once we establish the agreement of the class characteristics, we evaluate the individual characteristics Individual characteristics are unique marks caused by the manufacturing process. These marks cause striations on the bullet which can be used for comparison purposes.
Bullet Comparison Agreement of class characteristics Agreement of individual characteristics
Cartridge Case Comparisons Areas of comparison Breech face marks Firing Pin impressions Extractor marks Ejector marks Chamber marks
The marks on the breechface are caused by the manufacturing process. These marks are individual to that firearm. Different markings will be made by different manufacturing techniques and tool surfaces The marks from the breechface are transferred to the cartridge case during the firing process. Breechface Marks
Parallel Breechface Marks Parallel marks from the breechface transferred to the cartridge case
Parallel Breechface Marks
Parallel Breechface Marks
Circular Breechface Marks
Circular Breechface Marks
Arched Breechface Marks
Breechface Comparisons Using a comparison microscope, both cartridges can be viewed simultaneously.
Firing Pin Impressions Firing pins have different shapes which result in different markings on cartridges Firing pins are machined items and typically have markings from that machining process
Rectangular Firing Pin Marks
Rectangular Firing Pin Marks
Hemispherical Firing Pin Marks
Hemispherical Firing Pin Marks Notice the circular marks within the firing pin impression
Firing Pin Comparisons The individual characteristics within the firing pin impression can be viewed with a comparison microscope
The extractor is a piece of metal with a hook on the end designed to pull the cartridge from the barrel after firing. Extractor Marks
Extractor Marks The interaction of the extractor with the cartridge case results in markings both on and inside the rim of the cartridge case.
Extractor Comparison The marks made by the contact of the extractor with the rim of the cartridge case can be used for comparison
The ejector is designed to eject the fired cartridge case from the firearm Ejector Marks
Ejector Marks The ejector comes in contact with the cartridge as the slide moves rearward. When the ejector hits the cartridge, it is kicked from the slide and out of the firearm.
The contact between the cartridge case and the ejector results in an ejector mark Ejector Marks
Ejector Comparison Ejector marks can be used to compare cartridge cases under the comparison microscope
Chamber Marks Chamber marks are caused by imperfections in the barrel chamber. The marks are passed on to the cartridge case when it expands and is removed