Firearms Ballistics Firearms A Quick History Almost every

Firearms & Ballistics

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.

Firearms Identification • Often confused with the term ballistics • Ballistics is the study of a projectile in motion. – Inside the firearm – After it leaves the firearm – When it impacts the target

Firearms Identification of Firearms is based upon this basic idea: A harder object marks a softer one & imparts/transfers its microscopic irregularities to that object.

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

Forensic Firearms Expert • Bullet Comparison • Weapons Function – Is it safe? Has it been modified? • Serial Number Restoration • Gunpowder Residue Detection – on clothes, hands, & wounds • Muzzle-to-Target Distances

Pulling the Trigger • Pulling the trigger releases the firing pin… • The firing pin strikes the primer cup which holds the primer (explosive material and fuel) • The primer ignites the gun powder… • The powder generates large amounts of gas that propels the bullet forward through the barrel • The empty cartridge case is pushed out of the firing chamber by the extractor • Case is then pushed out of the gun by the ejector

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 into water and the casings and bullets are retrieved for comparison. • Goddard & Comparison Microscopes – Examined bullets side-by-side (to match striated markings).

Bullet Comparisons

Cartridge Markings All moving components contact the cartridge rather than the bullet can leave useful impressions on shell cartridges – Breechface marks- on rear of cartridge case of bullet – Firing pin impressions- on rear of cartridge case – Chamber marks- on side of casing – Extractor marks- on rims of case – Ejector marks- on side of case

Breechface Marks

Actual Breech Marks

Firing Pin Marks

Chamber Marks

Ejector Marks

Other Factors • Perfect matches sometimes difficult b/c: – Presence of grit & rust in a barrel – Recovered bullets too mutilated or distorted on impact • A spent bullet’s weight can sometimes determine the gun make. • General Rifling Characteristics File – FBI database of known land/groove width for all weapons.

Results can be: • Positive- striations match nicely and the suspect gun shot the questioned bullet found at the crime scene. • Negative- striations do not match at all and the suspect gun did not shoot the questioned bullet found at the crime scene. • Consistent- some striations match but others do not- inconclusive

Shotguns • Smooth barrel – 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)

Gunshot Residue (GSR) • GSR- substance released when a person shoots a gun • GSR Sources: – victim, clothing or target – shooter’s hands • Gunpowder Chemistry – Major detectable elements are: lead (Pb), barium (Ba) & antimony (Sb) – Virtually all cartridge cases are made of brass (copper & zinc); also detectable.

What do GSR Patterns Tell Us? • Interpretation of GSR pattern depends on the weapon and the kind and size of ammunition used. • Used to determine who fired the gun, the distance of the muzzle from the target, how recently the gun was fired, and the relative locations of multiple targets. • Point-blank- soot deposits are found around the bullet hole, no unburned powder will be found • Close range- GSR are deposited around the bullet hole with black soot and smoke, the pattern is small and dense. As the distance increases, the size of the pattern also increases. • Medium range- Between 1. 5 -3 feet, scattered gunshot residue will be seen around the bullet hole but without any black soot deposits. The pattern spreads out further as the distance between the shooter and the victim increases. • Long Distance range- Greater than 5 feet, GSR is usually not seen on the victim.

Collecting GRS at the Crime Scene. Should be collected as soon as possible and before fingerprinting is done. • 3 possible methods – GSR Adhesive Discs- collect GSR with adhesive disc and place disc in a sealed container, properly labeled. – Swabs- swabs are moistened with a 5% nitric acid solution, GSR is collected and swab is sealed in a container which is then labeled. – Send entire item to the lab for analysis (car or clothing).

Results of GSR Hand Test • Negative results may be caused by: – Washing the hands – Shooter may have been wearing gloves – Lead free ammunition • A rifle or shotgun may not deposit GSR on hands

GSR on the hand of a suicide victim, proving he was holding the weapon when it was fired.

DANGER GRAPHIC IMAGES!

Contact Gunshot wound This is a contact gunshot 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. An abrasion ring, formed when the force of the gases entering below the skin blow the skin surface back against the muzzle of the gun, is seen here in this contact range gunshot wound to the right temple.

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.

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.

END GRAPHIC IMAGES!

Bullet Trajectory Information bullet trajectories can help investigators discover♦ Where the shooter was standing ♦ Where the victim was standing ♦ Direction the gun was pointed ♦ Number of shots ♦ How far away the shooter was from the victim ♦ Possible sequence of several shots fired ♦ Bullet entry and exit holes ♦ Ricochet patterns

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 A. Photograph n B. C. • • • n n n n Sketch in position at the crime scene. Good Notes. When the firearm was found Was the safety on or off Was there live ammunition in the gun Make, model, caliber, and serial number of the gun. Location of any spent bullets or casings found Documentation of any bullet holes, or bullet damage

FIREARMS EVIDENCE COLLECTION n n D. Guns • Never wipe off the gun • Loaded guns should be unloaded at the scene, but documentation of live rounds in the gun should occur prior to unloading. E. Bullets and casings should be individually wrapped to prevent further scratches and when a doctor is removing a bullet from a victim, forceps should not be used.

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