Transcript Firearms and Ballistics

History of Firearms
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 14th century. Once it
was established that projectiles
launched with gunpowder had a
devastating effect on armored
knights, its use in weaponry was
vastly accelerated.
So, Why Gunpowder?
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.
Modern Gunpowder
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.
Forensic Analysis of Firearms
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.
Types of Firearms: Handguns
Handguns were conceived as an
easily-toted method for selfdefense. 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: Rifles
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 semiautomatic or automatic
(repeated firing with a single
pull.)
Types of Firearms: Shotguns
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.
Other Types of Firearms
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.
Ballistics
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.
Rifling
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.
Ammunition
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.
Bullets
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.
Gunshot Residue
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.
Firearms Evidence
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.
Two Types of Bullet Characteristics
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.
Class Characteristics
• Bullet Type
• Bullet Caliber
• Bullet Weight
• Lands and Grooves
• Rifling
• Cartridge Case
• Head Stamp
Individual Characteristics
• Striae
• Firing Pin Marks
• Breech marks
• Extractor marks
• Ejector Marks
• Chamber Marks
Ballistics Limitations
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.