Firearms Flashcards
Two general categories of firearms
Handguns
Long guns
Handguns are generally designed to:
be held and fired with one hand
Two classifications of handguns
single action
double action
Single action handguns
requires that the hammer be manually cocked back before each shot is fired
double action handguns
will automatically cock the hammer back when the trigger is pulled
will also reload the firing chamber after the current round is fired
Three types of handguns
single shot handguns
revolvers
semi automatics
Single shot handgun
can only fire one shot at a time
chamber needs to be manually loaded with a cartridge before each shot is taken
Revolvers
multiple firing chambers
chambers located within a rotating cylinder
cylinder rotates clockwise or counter clockwise as each shot is fired
each chamber holds a single cartridge
chambers line up with the barrel when rotated
cartridge casings have to be manually removed/ejected
Three types: swing out, break top, solid frame
Semiautomatic Handguns
removable magazine within the grip of the weapon
magazine is loaded with cartridges (live rounds)
load first round by pulling back the slide and causing the hammer to cock
once the slide is released the cartridge is loaded into the firing chamber
when the cartridge is fired, gases cause the casing to eject, the hammer is cocked, and the next round is loaded
one shot per trigger pull
Long guns are either:
rifles
shotguns
Long guns are designed to:
be fired while resting on the shoulder of the operator
there are differences in ammunition and barrel
Rifle Ammunition
traditional cartridge but larger in size
Rifle Barrel
has lands and grooves
Shotgun ammunition
shell: contains ball shaped projectiles called “shot”
Shotgun barrel
smooth
no lands or grooves
choke: narrowing of the barrel
single or double barreled
Double barrel can be horizontally or vertically situated
Can have different choke diameters
When a barrel is hollowed out by drilling:
microscopic striation marks are left
Random and unique markings
No two rifled barrels have identical striation markings
Caliber
diameter of the bore
Calibers are calculated by:
measuring the diameter between opposite lands
Caliber may not be an exact measurement:
bore diameter may fall within range
Caliber can be recorded in two ways:
hundredths of an inch
millimeters
What happens when a weapon is fired?
When the trigger of a gun is squeezed, a firing pin makes contact with the back end of the cartridge and ignites the explosive charge contained in the primer
The primer then ignites the propellant, or gunpowder, which is the main explosive component of a cartridge
What path does a bullet take when fired?
Travels through barrel
engaged by rifling
grooves guide bullet through barrel
rapid spin results
bullet travels on a true and accurate course - steady through air, does not tumble end over end
When attempting to link a bullet with a suspecting weapon, what should be compared?
the bullet and a test fired bullet from the suspected weapon
Because shot guns have smooth barrels, projectiles that pass through have:
no characteristic markings
The shot recovered at a crime scene can be weighted and measured for:
determination of the size of shot used in the shell
The size and shape of the recovered wad may also help determine:
the gauge of the shotgun used and may indicate the manufacturer of the fired shell
DRUGFIRE
Developed by the FBI in the 1990s
Emphasized cartridge case imagery but also included bullets
Used microscope and video camera for identification of individual characteristics
IBIS
Integrated Ballistic Identification System
Developed by the ATF in the 1990s
Processed digital microscopic images on bullets and cartridge casings
Incorporated two software programs: Bullet proof (analyzed bullets) and brasscatcher (analyzed casings)
NIBIN
National Integrated Ballistics Information network
1999
The FBI and ATF join forces
Unified system that incorporates DRUGFIRE and IBIS technologies
ATF is responsible for system sites
FBI is responsible for communications network
Without a weapon, recognizable characteristics are used
What is observed around the bullet hole?
Heavy concentration of residue
Scorch marks from flame discharge of weapon
Melted fibers
Stellate patterns
Halo of vaporous lead
bullet wipe around hole
Clothing collected at a scene may be submitted to the laboratory for presence of GSR if:
not readily visible due to color or patterns of clothing
The Dos and Don’t of Firearms Collection
Do assume the weapon is loaded and ready to fire
Do wear gloves
Do not insert a pencil or other object into the barrel for collection
Do hold the gun by the grp if latent fingerprints are a concern
Do make a weapon safe for transport. If you do not know how, do not assume you can figure it out. ASK.
If the weapon is a revolver, do photograph the cylinder in its position. Mark the chamber that is lined up with the barrel.
Do make a record of the positions of the safety and hammer upon collection and before making the weapon safe.
Do photograph any casings still left in the cylinder.
Do record the state of the firearm.
Do document all information on the firearm including serial number, make, model, and any other markings present.
If a weapon is found underwater, do collect it in a container with enough of the same water is it found in to keep it submerged. DO NOT attempt to dry or clean the weapon.
Do remove the magazine from the weapon and document the number of cartridges loaded.
Do make a note as to which rounds were removed from a magazine and which were removed from the chamber
Do package the weapon in a firearms box and secure it with plastic ties
Do make sure the box the weapon is packaged in is sealed over every open space
Firearms identification
a discipline primarily concerned with determining whether a bullet or cartridge was fired by a particular weapon
grooves
the cut, or low lying portions between the lands in a rifled bore
rifling
the spiral grooves formed in the bore of a fire arm barrel that impart spin to the projectile when it is fired
bore
the interior of a firearm barrel
lands
the raised portion between the grooves in a rifled bore; the original portion of the bore left after the groove have been imparted into a barrel
Caliber
the diameter of the bore of a rifled firearm, generally expressed in hundredths of an inch or millimeters
Gauge
the size designation of a shotgun; originally the number of lead balls with the same diameter as the barrel that would equal a pound
Breech Face Mark
the rear part of a firearm barrel
Extractor
the mechanism in a firearm that withdraws a cartridge or fired casing from the chamber
Ejector
the mechanism in a firearm that throws the cartridge or fired casing from the firearm
choke
an interior constriction placed at or near the muzzle end of a shotgun’s barrel to control or concentrate shot dispersion
Greiss Test
a chemical test used to examine patterns of gunpowder residues around bullet holes
