Ballistics

Job of Firearms Examiner Analyze bullets/casings to determine the type of weapon used Match bullet/casing to a specific weapon Match bullet/casing to a sample from another crime Crime scene reconstruction a) distance between muzzle and victim b) bullet trajectory

Ballistics Ballistics is 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 Path through a target

How a gun fires Pull trigger Firing pin strikes a cylinder of primer in the shell of the bullet Explosion pushes bullet through the gun’s barrel

Types of Guns Handguns a. revolver b. semiautomatic pistols c. machine pistols (automatics) Rifles Shotguns

Handguns: Revolver Think westerns Cartridge revolves Casing stays in cylinder Limited to six shots More accurate than semiautomatics

Handguns: Semiautomatic Pistols Loaded using magazine or clip Carry 15-19 rounds Clip is spring loaded Fires once for each pull of the trigger Empty case ejected

Automatic Weapons (machine pistols) Fire repeatedly as long as the trigger is depressed

Rifles Use a lever or sliding bolt to eject a spent cartridge and move next one into firing chamber More accurate and shoot more powerful cartridges than handguns

Comparison of Handgun and Rifle Bullets The metal casing encloses the powder, above which the bullet is seated. The powder is ignited through the flash hole when the primer is struck A case with a rim is found with revolver and lever action rifle cartridges, and also with some bolt action and semi-automatic rifles.

Shotguns Fire shells filled with pellets (shot) Shot spreads out in circular pattern Have no “rifling” inside the barrel Note: “rifling” are the spiral grooves inside the gun barrel that make the bullets spin.

Diagram of a Shotgun Shell At close range, the pellets (shot) act as one mass. The entrance wound would be about 1 inch in diameter and the wound cavity would contain wadding. At intermediate range (4-12 feet) the entrance wound is 2 inches in diameter and individual pellet markings are seen. Most pellets will not penetrate skin beyond 80 yards.

Intermediate range gunshot wound

Analyzing Bullets Always handle bullets carefully when collecting from a crime scene A bullet pried from a doorjamb, for example, should be checked for attached paint, fibers, or flesh Bullets removed from a body should be handled with surgical instruments during surgery

Types of bullets Low velocity – softer High velocity – harder Bullet shape is important in the wounding potential of the bullet

Lead Bullets Used in small caliber handguns and .22 and .25 caliber rifles They are soft and have less penetration

Lead Alloy Bullets These lead bullets have other metals added for hardness High velocity

Semi-Jacketed Bullets Have a thin brass coating Lead nose exposed May have a hollow point

Full Metal Jackets Completely covered w/ copper They are very high velocity bullets used by the military 45 AUTO, 230 grain full-metal -jacketed bullet. . .

Caliber Refers to the internal diameter of the barrel Measured in inches or mm Ex: .38 handgun –diameter of .38 inches

Shotgun Gauge Number of lead balls that it takes to weigh one pound Ex. 20 gauge shotgun: 20 lead balls = one pound

Marks Left on Casings 1. Impression left by firing pin a. center fire (primer in a cup) b. rim-fire (primer around the edge) 2. Breechblock patterns

Marks left on casing 3. Headstamps- info stamped by manufacturer 4. Extractor and ejector marks on side of casing automatic and semiautomatic weapons extractor: pulls next bullet into place ejector: push spent shell from weapon

Rifling Rifling refers to the spiral grooves etched inside the barrel They leave marks (striations) on bullets. Lands- high parts Grooves- low parts: Smooth bore rifles (shotguns) have no rifling and are not as accurate

Different gun types have different characteristics in their rifling. Ex. .32 Caliber Colt 6 lands and grooves with a left (counterclockwise) twist Ex. .32 caliber Smith and Wesson handgun 5 lands and grooves with a right (clockwise) twist.

Rifling FBI database keeps general rifling characteristic files for all weapons Machine that does the rifling becomes worn with use so each barrel is different

Rifling Firing of a gun wears down lands and grooves first bullet fired will have different striations than 100th bullet fired To confirm a match you need identical patterns on at least three consecutive striations on each bullet

Bullet patterns Patterns of Striations on Bullets

How to Make a Comparison Get an intact bullet from suspect weapon Fire bullet using the suspect weapon into a test firing chamber Compare lab-fired bullet to crime scene bullet using a comparison microscope

Databases Databases can be used if a suspect weapon is not available for comparison. The databases most commonly used are: IBIS- Integrated Bullet ID system (ATF) can connect two or more cases DRUGFIRE- FBI, focuses more on shell casings An expert makes the final match, not the computer.

Gunshot Residue (GSR) GSR occurs when gases and particulate matter escape through openings in the weapon and cling to hands, arms, clothing, face, walls, or the victim Pattern affected by wind, rain GSR can aid in distinguishing entrance from exit wounds (entrance will have more GSR) It can also help determine who fired a weapon—since it will appear on the shooter’s hands

GSR -Gunshot residue Soot on hand of a suicide victim, giving an indication that he was holding the weapon when it was fired

Griess Test Griess test is used to detect GSR Photographic or acetic acid paper is pressed over the area and soaked in reagent that will show the pattern of GSR Fades in 2 hours Detects byproducts of combustion such as lead, barium, antimony

Griess test

Gunshot residue Other testing is done by a swab of the area with filter paper Treat the paper with diphenylamine : ID metals by undergoing a color change. (blue is a positive result) False positives can be caused by: fertilizer, tobacco, cosmetics, urine Need confirmatory testing

Gunshot residue SEM- (scanning electron microscope) detects tiny GSR particles that have been exposed to high temp, are melted, and deformed

Determining Distance How GSR affects the wound area varies with the distance from the shooter to the victim Residue pattern on skin or clothing changes w/ distance Generally speaking, the more distance between the shooter and the victim, the wider the spread of GSR

Determining distance Test by use the suspect weapon on similar fabric at various distances such as: 6 inches, 1 ft, 18 inches, 2 ft, 3 ft Compare to victim’s clothing for match

Mechanism of ballistic injury

Gunshot Wounds Gunshot wounds are typically classified as Contact —have soot on the outside of the skin, and muzzle imprint, or laceration of the skin from effects of gases. (Close range = less than 6”) Intermediate range —show a wide zone of powder stippling, but lack a muzzle imprint and laceration. (6”-30”) Distance range —lack powder stippling and usually exhibit a hole roughly the caliber of the projectile fired. (greater than 30”)

The upper diagram illustrates the basic differences between the skin appearance of a contact, close (intermediate), and distant (indeterminant) range gunshot wound. The appearance of the wounding characteristics in the skull is shown in the lower diagram in which there is bevelling of the skull outward away from the direction of origin of the bullet.

Entrance wound on the left Exit wound on the right—vary in size and shape because the bullet can be deformed as it passes through the body. No exit wound means all the bullet’s energy was absorbed by the tissues.

Gunshot entrance wound to skull—notice heavy soot and radiating fracture lines

Exit wound No soot or powder, wound is a slit

Blood spatter Blood collects on hand of shooter

Terminal ballistics

Websites http://www.firearmstactical.com/wound.htm http://medlib.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNBLST.html excellent: tons of photos http://www.firearmsid.com/new_index.htm http://www.firearmsid.com/Case%20Profiles/FirearmID/FirearmID.htm great case studies with photos

Shot Number 12 shot .05 inches smallest Number 8 shot Number 4 shot largest