FIREARMS, TOOL MARKS, AND OTHER IMPRESSIONS Forensic Science - Chapter 16
Famous People Killed / Wounded with Guns • Abraham LincolnJohn LennonJohn F. KennedyRobert F. KennedyMartin Luther King Jr.Pope John Paul llMohandas GhandiFranz FerdinandMalcolm XBob MarleyRonald ReaganTheodore Roosevelt50 CentThe Notorious B.I.G.Tupac ShakurSean Taylor
Introduction • Structural variations and irregularities caused by scratches, nicks, breaks, and wear may permit the criminalist to relate: • A bullet to a gun • A scratch or abrasion mark to a single tool • A tire track to a particular automobile • Video part 1 Video Part 2 Video part 3 • Individualization, a goal of in all areas of criminalistics, frequently becomes an attainable reality in firearm and tool mark examination.
Father of Ballistics • Calvin Goddard, physician , acquired data from all known gun manufacturers in order to develop a comprehensive database. • Video FBI
Charles Waite - • Goddard his partner, Charles Waite, he catalogued the results of test-firings from every type of handgun made by 12 manufacturers. Waite also invented the comparison microscope. With this instrument, two bullets could be laid adjacent to one another for comparative examination.
TERMINOLOGY OF GUNS • Due to the multiple types, purposes, and cultures that have developed around firearms, a language of its own has developed. Before discussing the forensics of firearms, one must have a grasp on the terminology associated with guns. • We will look at different types of guns and their parts and uses.
TYPES OF GUNS • Modern firearms are manufactured in a variety of shapes and sizes to fit multiple purposes. • These include semi-automatic and even automatic weapons built primarily for military usage. Virtually any type of gun • can be found on the streets in use by youth gangs, persons involved in drug trafficking, "survivalists", and even what we would consider "ordinary" citizens.
HANDGUNS • Ahandgun was conceived as a compact weapon for self defense. • The two most common defensive handguns are the double action revolver and the semiautomatic pistol.
REVOLVERS • The revolver is the older type of handgun. It is less expensive, easy to use, simpler in design, and more reliable than semiautomatics. • However, compared to semiautomatic weapons, revolvers are limited to six shots, relatively slow to reload, less efficient, and the trigger pull is more difficult.
Revolvers • The revolver, the first multiple shot • hand gun, has several advantages they are less expensive, simpler in design, and more • reliable than semiautomatics. A revolver is • easy to use and are accurate. • However, compared to semiautomatic weapons, revolvers are limited to six shots, relatively slow to reload, less efficient, and the trigger pull is more difficult.
Revolvers Parts • If the barrel length is shorter, for ease of concealment, the gun becomes less accurate in hitting the target. • An ejector rod under the barrel is used to eject fired cartridges from the open cylinder before reloading. • The sights, which are lined up when aiming the weapon, on a revolver are usually a blade in the front and a notch on the rear.
Revolver Parts Continued • The frame is the largest part, and all other pieces attach to it. Frames are usually made of blued or plated steel, stainless steel, or lightweight alloys such as magnesium. The cylinder contains five or six holes for the cartridges and can be swung out for reloading. This must performed manually; the absence of cartridge cases at a crime scene may indicate the use of a revolver.
Parts of Revolver Continued • On a revolver, there is a gap between the cylinder and barrel to allow the cylinder to turn freely, this also allows gases and gun powder residue to escape laterally and allow the forensic pathologist to predict the location of a shooter more easily. • The inner mechanics of a revolver uses the energy from a trigger pull to rotate the cylinder, cocking the weapon, and then fall the hammer.
Revolver Parts continued Revolver with cylinder out for reloading Old Wild West Colt 45
Revolver Firing Mechanism • Revolvers can have one of two distinct • firing action designs. A single-action • revolver, the oldest and simplest action, • requires a shooter to cock the hammer back • before each pull of the trigger. SLOW. • In a double-actionweapon, a trigger pull will cock the weapon manually and fire the gun. This requires quite a bit more pressure and may compromise accuracy.
Semiautomatic Pistol • A more recent development than the revolver the pistol originated in the late 19th century. The advantages of semiautomatics stem from the use of recoil generated by the fired cartridge to eject the empty cartridge case, load the next cartridge, and cock the hammer. • This is more conducive to firing • multiple shots at multiple speeds. Many pistols are designed to carry 15 to 19 rounds.
HandgunsSemi-automatic Courtesy of C. Fanning Courtesy of C. Fanning Courtesy of C. Fanning
Semiautomatic Pistol Disadvantes • Disadvantages: • A more complicated mechanism requires more practice to use accurately, and is more likely to malfunction. • In addition, cartridge cases must be shorter to work well; because of this revolver cartridges are more powerful than semiautomatic cartridges.
Rifle Types • Rifles differ from handguns in the length of the barrel and the presence of a butt stock. • They are harder to carry, are poorly concealable, and more loosely regulated than handguns. • However, they are much more accurate and shoot more powerful cartridges than handguns. Rifles may be manufactured as • single shot; but, most commonly rifles possess bolt action, like. Military rifles are semiautomatic or automatic, having a detachable magazine holding 5 to 50 rounds.
Rifle Types Old Fashion Lever type rifle. Bolt action hunting rifle Semi-automatic hunting rifle
AUTOMATIC RIFLES • Automatic weapons are those weapons which will fire repeated rounds when the trigger is pulled and held. This allows the weapon to fire, reload and fire again as fast as the gun can possibly move. The most widely know automatic weapons are machine guns. • Most of these weapons are not legal, for personal use. It is possible for a skilled gunsmith to convert a semiautomatic • into a fully automatic weapon.
Parts of a Semiautomatic Rifle M1 carbine will fire each time you pull the trigger without manually reloading. The shells are held in the vertical clip under the receiver.
ASSAULT WEAPONS • Assault weapons are those weapons designed to kill mass numbers of people at a time. • The classification includes automatic weapons, machine guns, sawed off shotguns, grenade • launchers, and many other weapons used by the military.
Automatic Assault Rifles The most deadly gun that is commonly hand carried by the shooter. It can fire many rounds without reloading; as fast as you can pull the trigger and can be set to fully automatic mode.
Ballistic Fingerprinting • Ballistic fingerprinting refers to a set of forensic techniques that rely on marks that firearms leave on bullets to match a bullet to the gun it was fired with. Video – Ohio State forensics Class
Gun Barrel Markings • The inner surface of the barrel of a gun leaves its markings on a bullet passing through it. • These markings are peculiar to each gun. • The gun barrel is produced from a solid bar of steel that has been hollowed out by drilling. • The microscopic drill marks left on the barrel’s inner surface are randomly irregular and serve to impart a uniqueness to each barrel.
Bullet Recovery Tank • Each gun submitted is test fired and the recovered bullets and cartridge cases are retained for use in further analysis.
Recovered Bullets Video Alias Forensics video
Gun Barrel Markings • The manufacture of a barrel also requires impressing its inner surface with spiral grooves, a step known as rifling. • The surfaces of the original bore remaining between the grooves are called lands. • The grooves serve to guide a fired bullet through the barrel, imparting a rapid spin to insure accuracy.
Riflings in a Barrell Riflings are the groves that cause a bullet to spin and gain stability for a more accurate shot
Lands and Grooves Land Diameter Caliber Groove
Gun Barrel Markings • The diameter of the gun barrel, measured between opposite lands, is known as caliber. Most older guns’ calibers are measured in fraction of inches across the islands. So a 45 caliber bullet is 0.45 inches across. Some newer bullets are measured in millimeters. • Once a manufacturer chooses a rifling process, the class characteristics of the weapon’s barrel will remain consistent, each will have the same number of lands and grooves, with the same approximate width and direction of twist.
Striations • Striations, which are fine lines found in the interior of the barrel, are impressed into the metal as the negatives of minute imperfections found on the rifling cutter’s surface, or they are produced by minute chips of steel pushed against the barrel’s inner surface by a moving broach cutter. • These striations form the individual characteristics of the barrel.
Bullet Striations from the Barrel The striations on the bullet can make identifiable and unique markings that trace it back to a particular firearm.
Striations • It is the inner surface of the barrel of a gun that leaves its striation markings on a bullet passing through it. Courtesy of C. Fanning
Bullet Examination • No two rifled barrels, even those manufactured in succession, will have identical striation markings. • The number of lands and grooves and their direction of twist are obvious points of comparison during the initial stages of an examination between an evidence bullet and a test-fired bullet. • Any differences in these class characteristics immediately serve to eliminate the possibility that both bullets traveled through the same barrel.
The Comparison Microscope • The comparison microscope serves as the single most important tool to a firearms examiner. • Two bullets can be observed and compared simultaneously within the same field of view. • Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide.
Machine Guns Fully automatic machine guns can fire up to 1200 bullets per minute.
Rapid Fire Machine Gun Typical cyclic rates of fire are 500–900 RPM for assault rifles, 900-1,200 RPM for submachine guns and machine pistols, and 600-1,200 RPM for machine guns. M134
SHOTGUNS • Shotguns have a similar external appearance to rifles, but differ in the lack of rifling • inside the barrel, which is the basis for their legal definition. A shotgun shell may contain one large projectile (called a slug), a few pellets of large shot, or many tiny pellets. Shotguns are available in single shot (break action), double barrel, pump action, and semiautomatic. Unlike rifled firearms, a shotgun has a smooth barrel.