Firearms Ballistics Gunshot Wounds Part I STEM Firearms

Firearms, Ballistics, & Gunshot Wounds: Part I STEM

Firearms Identification • Discipline of forensic science which has as its primary concern the examination of bullets, cartridge cases, and other ammunition components to determine if they were fired in/from a specific firearm

Forensic Firearms Expert: Questions They Ask • Did a suspect use this gun to kill that person? • Did these bullets come from that gun? • Was it self-defense? • Is this a case of suicide, or is foul play involved?

Firearms Identification • A branch of toolmark examination, which considers: –a harder object marks a softer one and imparts/transfers its microscopic irregularities to that object

Firearms Identification • Often confused with the term ballistics • Ballistics is actually the study of a projectile in motion: – Inside the firearm – After it leaves the barrel of the firearm – When it impacts the target • (these last two often deal with trajectory)

Bullet & Cartridge Casing Examinations • Was a particular bullet or cartridge case fired in/from a specific firearm? – A comparison is made between an evidence bullet or cartridge case to known tests fired from a firearm

Typical areas of Identification on Cartridge Cases • Breech Face • Firing Pin Impression • Ejector Marks

Class Identification of a shell/bullet • First, the Class a shell or bullet belongs to is determined (i. e. , 9 mm or. 22 caliber) • When class characteristics are identified, the examinations progress to where an attempt is made to identify fired components based on individual characteristics

Individual Characteristics • When a firearm is manufactured, the individual parts are made with tools that are in a constant state of change • As a result, no two guns will leave the same marks on the ammunition components • The marks found on cartridge cases and bullets are sometimes referred to as striations

Area of Identification (rifling) on bullet • Individual characteristics are located within the rifling impressions on a bullet • They’re microscopic striations (or scratches) like those on the bullet below: Exhibit Test Fire

Gun Manufacture Videos

Gun Type Videos

Other Examinations routinely conducted in Firearms Identification • • Firearm function testing Examination of unfired ammunition Muzzle to target distance determination Restoration of serial numbers and other identification data • Toolmark to tool comparisons • Bullet trajectory • Gunshot residue of hands

Firearms: A Quick History • Almost every gun is based on the same simple concept: You apply explosive pressure behind a projectile to launch it down a barrel. • The earliest & simplest application of this idea is the cannon.

The 1 st handheld guns were essentially mini-cannons; you loaded some gunpowder & a steel ball & lit a fuse.

• War typically resulted in the need for improved weapons technology. • In the late 1800’s, the revolver quickly became popular due to it’s size & quick loading. – It only had to be reloaded every 5 -6 shots instead of after each shot.

• Handguns reigned supreme for the past 200 years & to this day, remain the most popular & readily available firearm.

Pulling the Trigger • • Pulling the trigger releases the firing pin… The firing pin strikes the primer… The primer ignites the gun powder… The powder generates gas that propels the bullet forward through the barrel & ejects the spent cartridge case.

Caliber: the diameter of the gun barrel. • Caliber is recorded in: – hundredths of an inch (. 22 &. 38) – millimeters (9 mm)

Bullet Anatomy

Anatomy of a Bullet

Bullet Comparisons • Each gun leaves distinct markings on a bullet passing through it. • A gun barrel is made from a solid bar of steel that has been drilled/hallowed out. • The drill leaves microscopic marks on the barrel’s inner surface.

Bullet Comparisons • Gun manufacturers also add spiral grooves to the barrel. This is known as rifling. • Lands: the space between the grooves. • As a spinning bullet passes through the barrel, it is marked by these grooves.

Class Characteristics • Class Characteristics: Once a manufacturer chooses a rifling process, for a particular class of weapon, they keep it consistent. • Lands & Grooves are the same for a model. –. 32 caliber Smith & Wesson has 5 lands & grooves twisting to the right. –. 32 caliber Colt has 6 lands & grooves twisting to the left. • Class characteristics can eliminate certain makes but are not enough to ID a particular gun.

Individual Characteristics • Imperfections in the manufacturing process make each barrel unique. • Rifled barrels, even if made in succession will NOT have identical striation (scratchlike marks).

Bullet Comparisons • To match bullets to a gun, test bullets must be fired through a suspect barrel for comparison. • Goddard & Comparison Microscopes – Examined bullets side-by-side (to match striated markings).

Bullet Comparisons

Cartridge Markings All moving components that contact the cartridge rather than the bullet can leave useful impressions on a shell cartridge – Breechface marks – Firing pin impressions – Chamber marks – Extractor & Ejector markings

Breechface Marks

Actual Breech Marks & Firing Pin Impressions

Firing Pin Marks

Chamber Marks

Ejector Marks

Shotguns • Smooth barrel (no rifling) – Projectile NOT marked as it passes through • Fire small lead balls or pellets contained within a shell. • Characterized by: – diameter of the shot – size & shape of the wad – Gauge: diameter of the barrel • ( gauge diameter)

SERIAL NUMBER RESTORATION – When a serial number is stamped into a gun, the metal underneath the number is compressed & hardened. – If the number is filed-off, the hardened area may still be present. – By using an acid solution the metal can be slowly eaten away. • In this process the softer metal will be eaten away first and the number may reappear.

Before & After – Historically, serial numbers are successfully restored 63% of the time on steel & 54% of the time for aluminum or zinc.

FIREARMS EVIDENCE COLLECTION n n n Make sure it is unloaded!!!!! DO NOT put a pencil into a barrel REVOLVERS n n AUTOMATICS n n n Indicate location of fired & unfired ammunition Check magazine for number of rounds Fingerprint magazine Place ID tag on trigger guard

FIREARMS EVIDENCE COLLECTION n AMMUNITION n Write on base or nose n Package in pill box or envelope n Wrap in tissue to protect

FIREARMS EVIDENCE COLLECTION n CLOTHING Protect & preserve any residue n Air dry if wet n Package separately in paper bags n n Establish CHAIN OF CUSTODY

Firearms Database n NIBIN - National Integrated Ballistics Information Network n Unsolved database for firearms evidence (like AFIS for fingerprints)

DANGER GRAPHIC IMAGES! Oh My…. .

This is a contact gunshot Contact Gunshot wound entrance wound. Since the barrel contacts the skin, the gases released by the fired round go into the subcutaneous tissue & cause the star-shaped laceration.

Abrasion Ring The abrasion ring, and a very clear muzzle imprint, are seen in this contact range gunshot wound.

Displayed here is an entrance at the left and an exit at the right. Exit wounds vary considerably in size and shape because the bullet can be deformed in its transit through the body. This is a contact range gunshot entrance wound with grey-black discoloration from the burned powder. There may be no exit wound at all if the bullet's energy is absorbed by the tissues. Some bullets (such a a "hollowpoint") are designed to deform so that all their energy will be converted to tissue damage and not exit.

• Powder tattooing is seen in this intermediate range gunshot wound. The actual entrance site is somewhat irregular, because the bullet can tumble in flight.

• The surface of the skull demonstrates the heavy soot in this contact range entrance wound, as well as radiating fracture lines. The direction of fire was thus toward the back of this picture.

Blood Spatter With a contact or very close range gunshot wound, it is possible to have blood spatter as well as GSR on the hand of the person firing the weapon.

Trajectory