Firearms and Ballistics

Forensic Firearms Identification A scientific process of determining whether a bullet or cartridge cases was fired from a particular weapon. This is done by examining and evaluating the class and individual characteristics imparted onto the bullet or cartridge case.

Ballistics - definition Ballistics: to “throw” Ballistics is the science of the mechanics of motion, and the effects of projectiles (bullets) on targets. 3

Firearm Identification One can determine the following with the help of forensic ballistics: Type of bullet Type of firearm Serial number on weapon (even if it is sanded off) Gunshot residue (GSR) patterns on hands, clothes, wounds The estimation of muzzle-to-target distances

First, a little history lesson. The invention of gunpowder led to the development of firearms. Gunpowder first appeared in use in China over a thousand years ago, but was used primarily in firecrackers and only sparingly in weapons for military use (canons)

Types of Firearms Pistols Revolvers Rifles Shotguns

Pistols and Revolvers

Rifles and Shotguns

The Evolution of the Bullet Cartridge The next major innovation in the history of firearms was the bullet cartridge. Simply put, cartridges are a combination of a projectile (the bullet), a propellant (gunpowder, for example) and a primer (the explosive cap), all contained in one metal package.

Components of a Bullet Cartridge Cartridge –This is a self-contained unit that includes an outer casing, projectile (bullet), propellant (gunpowder), and primer (source of ignition).  Only the projectile is fired from the gun.  The remainder of the spent cartridge is ejected from the weapon. Cartridge casing –usually made of brass, steel and aluminum. Better quality cases can be reloaded and reused. Bullet –the projectile that is loaded into a cartridge and fired from a firearm.

Primer – The primer fits into the butt of the cartridge casing or shotgun shell.  It contains an explosive chemical. When the trigger is pulled on a firearm, a firing pin is slammed into the primer.  This collision causes the primer to explode and ignite the gunpowder. A primer is a small copper or brass cup, containing a precise amount of stable but shock-sensitive explosive mixture. Jacket – The metal covering over a bullet that overlies a core of different consistency.  Jackets are used to manipulate the degree of deformation that occurs upon impact.

More about bullets Bullets come in many shapes and sizes They are made of either soft metals like lead or hard ones like bronze. They can be hard if they are solid, or soft, if they have a hollowed tip (hollow-point or hollow-tip. They are either partially or completely covered by a jacket – usually made of copper. (Hence the phrase “Full Metal Jacket”)

Solid Bullets Made of bronze, copper-nickel alloys

Soft-point Bullet a.k.a soft-nose bullet A soft-point bullet, also known as a soft-nosed bullet, is a lead bullet with a copper or brass jacket that is left open at the tip, exposing some of the lead inside.

Hollow-point bullets a.k.a. hollow-nose Contain a hollow portion in the tip Hollow-tip bullets are designed to “mushroom” upon impact - to cause more tissue damage – used for hunting. They can be partially jacketed (soft-point) or fully jacketed If they are partially jacket, they are called soft-point hollow nose bullets Soft-point hollow nose Full metal jacket hollow nose

Expansion Physics One can observe the damage done by a projectile and determine the type it was (if it is not found) This is a 30 caliber soft-point bullet that mushroomed and probably caused more damage than just a hole the width of the original bullet.

The Firing of a Pistol

Rim-fire vs. Center-fire Cartridges Center-fire cartridges are usually more powerful than rim-fire ones.

Forensics of Firearms Structural variations and irregularities permit the forensic scientist to relate a bullet to a gun. Individualization is attainable! Not just through comparison of bullets, but through weapon comparison, restoration of serial numbers on weapons, gunpowder residues on garments and around wounds, powder residues on hands, and estimation of muzzle to target distance.

Class Characteristics of Firearms Class characteristics are measurable features of a specimen that indicate a group source. They result from design factors, and are determined prior to manufacture. Examples are caliber, firing pin shape, and general rifling characteristics.

Gun Barrel Markings The inner surface of the barrel of a gun leaves its markings on a bullet passing through it. These markings are particular 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 uniqueness to each barrel.

Caliber The diameter of the gun barrel is measured between opposite lands, this is known as the caliber of the weapon. It is usually expressed in hundredths of an inch (.22) or millimeters (9 mm). So if the diameter is .32 inches, it is a .32 caliber bullet. The decimal point is generally dropped when spoken, making it “thirty-two caliber".

Caliber Caliber – the diameter of the bore of a rifled firearm.

RIFLING Helical grooves impressed in the bore of a firearm barrel to impart rotary motion to a projectile. Grooves – the indentations Lands – The surfaces of the original bore.

RIFLING

GENERAL RIFLING CHARACTERISTICS The number, width and direction of twist of the rifling grooves in a barrel of a given caliber firearm.

What is the purpose of rifling? It imparts spin to the projectile when it is fired and prevents the bullet from tumbling when it leaves the barrel.

Rifling Every firearms manufacturer chooses a rifling process that is best suited to meet the production standards and requirements of its product. Once the choice is made, the class characteristics of the weapons barrel will remain consistent; each will have the same number of lands and grooves, the same approximate width and directions of twist. Rifling does NOT impart individual characteristics to the barrel!

For example … .32 caliber Smith & Wesson revolvers have five lands and grooves twisting to the right. .32 caliber Colt revolvers exhibit six lands and grooves twisting to the left.

Firing a Weapon Pulling the trigger serves to release the weapon’s firing pin, causing it to strike the primer, which in turn ignites the powder. The expanding gases generated by the burning gunpowder propel the bullet forward through the gun barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechblock. The shell is impressed with markings by its contact with the metal surfaces of the weapon’s firing and loading mechanisms.

The Firing of a Pistol

Manual, Semi-automatic and Automatic In manual guns, the user must insert a round into the chamber, either manually or through the action of the weapon between shots. In semi-automatics, a trigger pull is needed per round fired. For example, to fire ten rounds in a semi-automatic firearm, the trigger would need to be pulled ten times (once for each round fired) In contrast, a fully automatic firearm, can continue to fire as long as the trigger is held pulled or until it runs out of ammunition.

Cartridge Case Markings The shape of the firing pin will be impressed into the relatively soft material of the primer on the cartridge case. The cartridge case, in its rearward thrust, is impressed with the surface markings of the breechblock.

Cartridge Case Markings Other distinctive markings that may appear on the shell as a result of metal to metal contact are caused by the: Extractor, which is the mechanism in a firearm by which a cartridge of a fired case is withdrawn from the firing chamber. Ejector, which is the mechanism in a firearm that throws the cartridge or fired case from the firearm. Magazine or clip, which is the mechanism that in a firearm holds the bullets.

Breech face of a firearm. Arc breech face marks. Breech face of a firearm.

PARALLEL BREECH FACE MARKS

BREECH FACE GRANULAR MARKS CIRCULAR MARKS

FIRING PIN IMPRESSION

OTHER MARKS Ejector marks Extractor marks

Ejector and Extractor Marks Used cartridge casings are first removed from the chamber by extractor mechanisms. The casings are then dragged across the edge of the ejection port as they are ejected from the weapon. These extractor and ejector marks can be matched.

BULLET EXAMINATIONS Striations, which are fine lines found in the interior of the barrel, are impressed into the metal of the bullet as it passes through. These striations are produced during the rifling process. Striations form the individual character of the barrel. It is the inner surface of the barrel of a gun that leaves its striation markings on a bullet passing through it.

BULLET EXAMINATION The random distribution and irregularities of the striations are impossible to duplicate exactly in any two barrels. The number of lands and grooves and their direction of twist can serve as class characteristics, but the striations are the individual characteristics necessary to determine a match.

SHOOTING TANK

COMPARISON MICROSCOPE

BULLET COMPARISON The striations of the bullet are lined up and compared.

SHOTGUNS Unlike, rifles, shotguns have a smooth barrel. Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon. The diameter of the shotgun barrel is expressed by the term gauge. The higher the gauge number, the smaller the diameter.

Shotgun Shells The “bullet” part of the shotgun shell can either be tiny pellets or “shot” that spray out or a single “slug”. (Wad)

SHOTGUNS The examination of the shot pellets or buckshot can determine the size or gauge of the shotgun. Gauge – the number of lead pellets with the same diameter as the barrel that would make a pound. For example, a 12 gauge shotgun would have a bore diameter of a lead pellet 1/12 lb. **These are not the pellets that are fired from the shotgun! Only used to measure gauge.

SHOTSHELL COMPONENTS

BUCK SHOT

Chokes Chokes are often used on shotguns to constrict the end of the barrel. A narrow choke will increase both the speed and distance that the shot will travel.

IBIS and NIBIN Automated Ballistic Identification Systems (ABIS) are specialized computer hardware/software combinations designed to capture, store and rapidly compare digital images of bullets and cartridge casings. Integrated Ballistic Identification System Automated firearms identification Developed for the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) Uses several computer programs to help identify firearms In 1999, the FBI and ATF consolidated their resources and came up with the NIBIN (National Integrated Ballistics Identification Network)

SERIAL NUMBER RESTORATIONS Obliterated and/or altered firearm serial numbers can sometimes be restored. Chemical, electrolytic, and magnetic particle inspection are some of the methods used.

Before restoration. After restoration.

GUNPOWDER RESIDUE When a firearm is discharged, unburned and partially burned particles of gunpowder in addition to smoke are propelled out of the barrel along with the bullet toward the target. If the muzzle of the weapon is sufficiently close, these products will be deposited onto the target. The distribution of gunpowder particles and other discharge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired.

GUNPOWDER RESIDUE The precise distance from which a handgun or rifle has been fired must be determined by means of a careful comparison of the powder-residue pattern located on the victim’s clothing or skin against test patterns made when the suspect weapon is fired at varying distances from a target. By comparing the test and evidence patterns, the examiner may find enough similarity in shape and density upon which to base an opinion as to the distance from which the shot was fired.

GUNPOWDER RESIDUE In cases where the weapon is held in contact with or less than one inch from the target, a star-shaped (stellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead is usually present. A halo of vaporous lead (smoke) deposited around a bullet hole is normally indicative of a discharge of 12 to 18 inches or less. The presence of scattered specks of unburned and partially burned powder grains without any accompanying soot is often observed at distances up to 25 inches (and occasionally as far as 36 inches). More than three feet will usually not deposit any powder residues, and the only visual indication is a dark ring around the hole, known as a bullet wipe.

Contact Pattern Shotgun

THREE INCH PATTERN

GUNPOWDER RESIDUE When garments or other evidence relevant to a shooting are received in the crime laboratory, the surfaces of all items are first examined microscopically for the presence of gunpowder residue. Chemical tests, such as the Greiss test, may be needed to detect gunpowder residues that are not visible. The firing distances involving shotguns must again be related to test firing. The muzzle to target distances can be established by measuring the spread of the discharged shot.

Greiss Test A test conducted on or around bullet holes to pick up residues of unspent gun powder. Nitrites are a found in incompletely burned powder (Nitrocellulose is found in modern smokeless powders and nitrites are the “leftovers”) When the Greiss reagent is added to a nitrite-containing sample, it turns pink.

Positive Greiss Test

PRIMER RESIDUE ON HANDS The firing of a weapon not only propels residues toward the target, but gunpowder and primer residues are also blown back toward the shooter. As a result, traces of these residues are often deposited on the firing hand of the shooter.

PRIMER RESIDUE ON HANDS Examiners measure the amount of barium and antimony on the relevant portion of the suspect’s hands, such as the thumb web, the back of the hand, and the palm.