Firearms and Ballistics - PowerPoint Presentation

Slide1

Firearms and BallisticsSlide2

Mankind has been fascinated by the idea of

launching a projectile at animals for thousands of years.Gunpowder was first used in China over 1000 years ago, but was primarily used in firecrackers and only rarely in military weapons.The use of gunpowder migrated to Europe in the 14

th

century. Once it was established that projectiles launched with gunpowder had a devastating effect on armored knights, its use in weaponry was vastly accelerated.

History of FirearmsSlide3

Gunpowder is made from a mixture of

sulfur, charcoal, and saltpeter (potassium nitrite).1 mole of solid gunpowder, when ignited, will produce 6 moles of gas—hence, a big whooooosh!Add this amount of

expanding gas

to a small metal tube and it will drive a projectile out at high speed in a specific direction. The firearm was born.

So, Why Gunpowder?Slide4

Modern methods of

manufacturing have refined gunpowder’s original ingredients to produce the maximum amount of expansion with the least amount of residue (leftover powder.)The manufacture of modern powders is standardized enough that gunpowder residue can be analyzed by methods which identify specific components, which can be used in forensic analysis

.

Modern GunpowderSlide5

Modern firearms are manufactured in a

variety of shapes and sizes to fit multiple purposes. The proliferation of guns in the U.S. has made the forensic scientist’s job very difficult. The sheer numbers of guns and the astonishing variety of makes keeps the scientists very busy.Today, virtually any military gun (including automatic weapons) can be found used by

gang members

, drug traffickers, paramilitary “survivalists,” or the “average” citizen.Forensic Analysis of FirearmsSlide6

Handguns were conceived as an easily-toted method for

self-defense. As such, handguns are compact to make them easy to hide and carry. They are heavily controlled and regulated in most states for these reasons.Since no one is guaranteed a perfect shot, handguns must be able to provide more than one shot.The two most common handgun types are double-action revolvers

and

semi-automatic pistols.Types of Firearms: HandgunsSlide7

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.Military rifles can be semi-automatic or automatic (

repeated firing with a single pull

.)Types of Firearms: Rifles Slide8

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.

Types of Firearms: ShotgunsSlide9

Automatic pistols

, like the Uzi, are used by some crime syndicates but are too expensive for the average criminal.Air guns (BB guns) shoot a projectile by using compressed air, instead of gun powder. A chamber of compressed CO2 is attached. In most states, air guns are not regulated as firearms, despite both homicides and suicides involving these machines.Other Types of FirearmsSlide10

The term

ballistics refers to 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, and path through a target.How much damage the

projectile

can produce is dependent upon the length of the barrel. Higher velocities can be generated with a longer chamber. Rifles cause more damage.

BallisticsSlide11

In the 18th century, gunsmiths discovered that putting

spiral grooves in the bore would impart a spin to the bullet that improved accuracy markedly. Modern weapons have metal lands and grooves with a twist inside the barrel of the gun, called rifling. This rifling is slightly different for each weapon, imparting different patterns of deformation on the bullet. These patterns can be used to identify

a

particular weapon used in a crime.RiflingSlide12

Ammunition

consists of projectiles, such as bullets and shot, together with their fuses and primers, that can be fired from guns or otherwise propelled. When shot from a gun, the bullet cartridge either stays in the chamber or is ejected after firing. AmmunitionSlide13

Bullets are made of

lead; sometimes jacketed with brass, copper, or steel.Bullet size is determined by the diameter which is called the caliber or gauge

. In general, the larger the diameter, the more

damage that is inflicted.BulletsSlide14

Whenever a gun is fired, the

shooter gets sprayed with an invisible blast of chemical residues that are byproducts of the incomplete combustion of gunpowder, primer, and lubricants. This is called gunshot residue.Gunshot residue can also be found on the victim’s body or clothing. Depending upon how far away the victim is from the weapon, different types of residue are seen.

Gunshot ResidueSlide15

If a bullet is recovered from the

scene or from the body, it may be compared to bullets obtained by test-firing the suspected weapon. This is done with similar ammunition.Bullets are marked in the 12 o’clock position so that a reference point can be compared. Test firings are then made into a tank of water

. The bullets are

recovered and compared for similar lands and grooves. This can be very difficult if the bullet has been deformed after firing.

Firearms EvidenceSlide16

Class characteristics

refers to the type of caliber and rifling. Rifling pattern may turn to the right or left, with a given rate of twist. The number and depth of grooves can vary also. The same type of gun will produce class characteristics.Individual characteristics refers to imperfections within the barrel of a particular gun. These comparisons allow a particular bullet to be linked to a

specific

firearm.Two Types of Bullet CharacteristicsSlide17

Bullet

TypeBullet CaliberBullet WeightLands and GroovesRifling

Cartridge Case

Head StampClass CharacteristicsSlide18

Striae

Firing Pin MarksBreech marks Extractor marksEjector MarksChamber

Marks

Individual CharacteristicsSlide19

Bullet and cartridge markings cannot be used with

shotguns, since they fire shot-containing cartridges. In many cases the shot rides inside a plastic sleeve that prevents it from ever touching the barrel, and even in cases where the shot does touch the barrel, the random movement of the shot down the barrel will not leave any consistent marks. However, shotgun cases can still be examined for

firing pin

marks. Ballistics Limitations