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BALLISTICSHandguns & Rifles
Introduction Structural variations and irregularities
caused by scratches, nicks, breaks, and wear may permit the criminalist to relate: A bullet to a gun A scratch or abrasion mark to a single tool A tire track to a particular automobile
Individualization, a goal of in all areas of criminalistics, frequently becomes an attainable reality in firearm and tool mark examination.
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HANDGUNS
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Firearm Investigation• Firearms produce
characteristics on the ammunition to help identify the type of weapon that was used to fire it.
• If only fired ammunition is found, it may be possible to determine the model of firearm that was involved
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Aspects of Firearm Investigation
• Identifying the type of ammunition from used bullets, cartridge cases, marks and residue
• Linking crimes when the same weapon was used
• Estimating the distance the weapon was from the target when it was fired
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Aspects of Firearm Investigation
• Determining the location of the shooter from the direction of travel of bullets and location of spent cartridge shells
• Restoring serial numbers that have been scratched off in effort to disguise a weapon
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Evidence
Typical evidence left on scene may include
1. Recovered weapons
2. Fired and unfired cartridges
3. Silencers
4. Magazines
Firearm Evidence Collection Firearms are collected by holding the weapon
by the edge of the trigger guard or by the checkered portions of the grip.
Before the weapon is sent to the laboratory, all precautions must be taken to prevent accidental discharge of a loaded weapon.
In most cases, it will be necessary to unload the weapon.
When a revolver is recovered, the chambers, their positions, and corresponding cartridges must be recorded.
Firearm evidence must be marked for identification (usually a tag on the trigger guard) and a chain of custody must be established.
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Firearm Evidence Collection Bullets recovered at the crime scene are scribed with
the investigator’s initials, either on the base or the nose of the bullet.
The obliteration of striation markings that may be present on the bullet must be scrupulously avoided.
The investigator must protect the bullet by wrapping it in tissue paper before placing it in a pillbox or an envelope for shipment to the crime laboratory.
Fired casings must be identified by the investigator’s initials placed near the outside or inside mouth of the shell.
Discharged shotgun shells are initialed on the paper or plastic tube remaining on the shell or on the metal nearest the mouth of the shell.
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The Modern Cartridge
1. The bullet itself, which serves as the projectile
2. The casing which holds all parts together
3. The explosive, for example gunpowder or which serves as a propellant
4. The rim, at the base of the cartridge
5. The primer which ignites the propellant.
A modern cartridge is made up of five components:
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Types of Bullets
• Full Metal Jacket
• Round Nose
• Hollow Point
• Wadcutter
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FMJ vs. Hollow-Point• Ball ammunition - designed to keep
it's shape and form upon impact. • Hollow-point/defensive ammunition is
meant to deform & expand upon hitting a solid obstacle.
• Self-defense rounds tend to leave their energy in the object hit
• Ball ammunition will continue through the object and thus tend to damage less but risk possible over penetration.
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Ball Ammunition
• Projectiles will keep their shape and mass when hitting an object and continue on
• Will not cause a large temporary or permanent wound cavity.
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Hollow Point Ammunition• Specifically designed to expand when it
strikes solid material. The hollow-point projectiles have a hollow indentation at the front of the projectile which is designed to mushroom open upon contact.
• Energy contained in the round is expanded very quickly in a small distance, and the temporary wound cavity as well as the permanent wound volume is much larger than that of practice rounds.
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Hollow Point Ammo
Handguns Single-shot pistols
Fire only one round at a time Revolvers
Feature several firing chambers within a revolving cylinder
Include swing-out revolvers, break-top revolvers, and solid frame revolvers
Semi-automatic pistols Feature a removable magazine Fire one shot per trigger pull
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Revolver• Handgun that has a cylinder with
holes that contain cartridges. The cylinder revolves to bring the cartridge into position to be fired.
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Revolver
• Less expensive
• Simple design
• More reliable and accurate than semi-autos
• Able to fire the most powerful and largest cartridges
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Revolver
• Cylinder contains on average 5 to 7 holes for the cartridges and can be swung out for easy reloading. No cartridge cases will be found at a crime scene unless the suspect stopped to reload or picked up the empty cases
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Revolver
• There is a gap between the cylinder and barrel to allow the cylinder to turn freely, but this allows gases to escape, which at close range may deposit gunshot residue on surrounding areas and allow the CSI to reconstruct the scene.
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Semi Automatic
• Forces generated by the burning gunpowder force the slide backwards against a spring. Cartridges are loaded into a spring-loaded magazine and inserted into the grip of a weapon. As the slide is forced back by the firing of the weapon, the empty cartridge case is extracted from the chamber and ejected from the weapon, and a new cartridge is stripped off the magazine and fed into the chamber as the slide moves forward.
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Semi Automatic
• The advantage of semi-auto handguns is the use of recoil generated by the fired cartridge to eject the empty cartridge cases, load the next cartridge, and cock the hammer.
• Able to carry numerous rounds; some up to 20
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Semi Automatic Casings
• Empty cartridge cases may land from 2-20ft. from the fired gun.
• Ejected cases may be hard to find as they may roll into a hiding place such as grass or under objects. Ejected cases will virtually always be left behind at the scene
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Firearm Barrel
• The barrel of a firearm is a metal tube made by drilling out a steel rod. The barrel is typically rifled
Gun Barrel Markings The inner surface of the barrel of a gun
leaves its markings on a bullet passing through it.
These markings are peculiar to each gun. The gun barrel is produced from a solid
bar of steel that has been hollowed out by drilling.
The microscopic drill marks left on the barrel’s inner surface are randomly irregular and serve to impart a uniqueness to each barrel.
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Gun Barrel Markings The manufacture of a barrel also requires
impressing its inner surface with spiral grooves, a step known as rifling.
The surfaces of the original bore remaining
between the grooves are called lands.
The grooves serve to guide a fired bullet through the barrel, imparting a rapid spin to insure accuracy.
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Gun Barrel Markings The diameter of the gun barrel, measured
between opposite lands, is known as caliber.
Once a manufacturer chooses a rifling process, the class characteristics of the weapon’s barrel will remain consistent, each will have the same number of lands and grooves, with the same approximate width and direction of twist.
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Striations Striations, which are fine lines found in the interior
of the barrel, are impressed into the metal as the negatives of minute imperfections found on the rifling cutter’s surface, or they are produced by minute chips of steel pushed against the barrel’s inner surface by a moving broach cutter.
These striations form the individual characteristics of the barrel.
It is the inner surface of the barrel of a gun that leaves its striation markings on a bullet passing through it.
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Bullet Examination No two rifled barrels, even those manufactured
in succession, will have identical striation markings.
The number of lands and grooves and their direction of twist are obvious points of comparison during the initial stages of an examination between an evidence bullet and a test-fired bullet.
Any differences in these class characteristics immediately serve to eliminate the possibility that both bullets traveled through the same barrel.
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The Comparison Microscope
The comparison microscope serves as the single most important tool to a firearms examiner.
Two bullets can be observed and compared simultaneously within the same field of view.
Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide.
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The Comparison MicroscopeGoddard – Inventor of the Comparison Microscope
The Comparison Microscope
Consists of two microscopes connected to an optical bridge that results in a split view window.
A device used to analyze side-by-side specimens is called a comparison microscope.
Used in forensic sciences to be able to compare microscope patterns and identify or deny their common origin. Handguns predominated as the firearm of choices in shooting-related crimes, especially in the United States of America
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Land and Groove Impressions
Rifling refers to the groves cut inside the surface of the barrel.
The uncut metal is known as the land.
As the bullet travels along the barrel, it will scrape against the rifling as it heads out the muzzle.
The bullet will now show the marks of the groves in the rifled barrel
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Land and Groove
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Land and Groove• Each barrel has
its own unique set of imperfections in the rifling
• Close examination of a bullet for these marks allows it to be matched to a particular weapon that fired it
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Distinctive Marks
• When the weapon is fired, the firing pin strikes the primer of the cartridge resulting in contact marks and indentations
• When the cartridge is ejected from the gun, this may leave gouged impressions on the rim and head of the case
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RIFLES and SHOTGUNS
Long Guns
Long guns may be single-shot, repeating, semi-automatic, or automatic.
Shotguns Shell ammunition contains numerous ball-shaped
projectiles, called shot Narrowing of the smooth barrel, called the choke
of the shotgun, can concentrate shot when fired
Rifles Feature a barrel with lands and grooves Bullet ammunition is impressed with lands and
grooves during firing 39
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Pump Action
Rifle
Shotgun
With a pump action weapon a suspect could easily clean up spent
cartridges or shells.
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Semi-Automatic
Shotgun
Rifle
This weapon would spray spent cartridges all over the place,
investigators would most likely find spent cartridges.
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Bolt-Action
Rifle
This would enable a suspect to take the cartridge with them.
Shoatgun
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Other
Side by side
Over/Under
Suspect can take spent shells.
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Muzzleloader
Most commonly a rifle, but they do make shotguns. If this were used in a crime it would leave a lot of evidence do the burning of black powder. You may find a sabot and a primer but no cartridge.
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Automatic
This is illegal to own in the United States
Military and law enforcement agencies use them.
Criminals do get a hold of them and they usually have the high capacity magazines to go with them.
Leaves spent cartridges all over the place.
This M-4 can be equipped with a 90 round magazine. This magazine is legal to purchase in most states.
Shotguns Unlike rifled firearms, a shotgun has a smooth
barrel.
Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon.
The diameter of the shotgun barrel is expressed by the term gauge.
The higher the gauge number, the smaller the barrel’s diameter. 46
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Shotgun Shells
12ga
2 3/4
12ga
3
12ga
3 1/2
These come in 10,12,16,20,28 gauge and .410 caliper. Smaller the number bigger the shell. They are filled with different types of shot for different purposes.
All these types of shot leave a different mark.
12ga
2 3/4
12ga
3
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Rifle Cartridges
Rifles fire a bullet. It rides down the barrel and the rifling in the barrel forces it to spin making it stable in flight. The rifling also leaves a mark on the bullet “Lands and Groves”. Investigators can use these marks to find out what kind of gun the bullet came from.
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Caliber
30-06 Springfield, 458 Winch.
Caliber is 100ths of an inch, for example 1 inch is 100 caliber. Rifle cartridges come in hundreds of sizes. Each gun is made for a specific cartridge. If investigators find a bullet at a crime scene they can find out what caliber it is and what kind of lands and grooves it has. Then they might be able to find out what kind of gun fired it.
45-70 Gov’t., 223 Remington
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Shot
Wad
Slug
Buffer/Gas Seal
Shell “Hull”
Evidence One Might Find at a Crime Scene
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Shotgun Evidence
Possible pieces of evidence that might be found if a SHOT GUN was used. The suspect could take the hull depending on the action used, but it is unlikely they would find the other parts of the shell. Where these parts are found could show the direction of fire.
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Bullets
Cartridges
This is what you might would find at the scene of a crime if a RIFLE was
used.
Evidence One Might Find At A Crime Scene
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Any time a gun is fired there will be gun shot residue. It is possible to match gun shot residue at
a crime scene to gun shot residue on a suspect. When the gun is fired the person firing it gets the
residue on their hands.
Gun Shot Residue
Gun shot residue under a microscope
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Firing Pin Drag Marks
A mark is left on the primer after a round is fired. These marks can be used to find out
what gun the round was fired out of.
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These are CENTERFIRE cartridges. They are called this because the primer is in the
center. The firing pin mark on the left is off center on the primer. This can be used to
identify the weapon that fired it.
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This is a RIMFIRE cartridge. You can not see the primer because it runs around the
rim of the cartridge. The firing pin mark would be on the edge.
Firing a Weapon The act of pulling the trigger serves to release the
weapon’s firing pin, causing it to strike the primer, which in turn ignites the powder.
The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechblock.
The shell is impressed with markings by its contact with the metal surfaces of the weapon’s firing and loading mechanisms.
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Cartridge Case Comparison The firing pin, breechblock, and ejector and
extractor mechanism also offer a highly distinctive signature for individualization of cartridge cases.
The shape of the firing pin will be impressed into the relatively soft metal of the primer on the cartridge case.
The cartridge case, in its rearward thrust, is impressed with the surface markings of the breechblock.
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Cartridge Case Comparison Other distinctive markings that may appear
on the shell as a result of metal to metal contact are caused by the: Ejector, which is the mechanism in a firearm that
throws the cartridge or fired case from the firearm.
Extractor, which is the mechanism in a firearm by which a cartridge of a fired case is withdrawn from the firing chamber.
Magazine or clip, which is the mechanism that in a firearm holds the bullets.
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Computerized Imaging The advent of computerized imaging technology
has made possible the storage of bullet and cartridge surface characteristics in a manner analogous to automated fingerprint files.
The National Integrated Ballistics Information Network, NIBIN, produces database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, often linking a specific weapon to multiple crimes.
It is important to remember, however, that the ultimate decision for making a final comparison will be determined by the forensic examiner through traditional microscopic methods.
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Gunpowder Residue When a firearm is discharged, unburned and
partially burned particles of gunpowder in addition to smoke are propelled out of the barrel along with the bullet toward the target.
If the muzzle of the weapon is sufficiently close, these products will be deposited onto the target.
The distribution of gunpowder particles and other discharge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired.
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Gunpowder Residue The precise distance from which a handgun or rifle
has been fired must be determined by means of a careful comparison of the powder-residue pattern located on the victim’s clothing or skin against test patterns made when the suspect weapon is fired at varying distances from a target.
By comparing the test and evidence patterns, the examiner may find enough similarity in shape and density upon which to base an opinion as to the distance from which the shot was fired.
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Gunpowder Residue In cases where the weapon is held in contact with or
less than 1 inch from the target, a star-shaped (stellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead is usually present.
A halo of vaporous lead (smoke) deposited around a bullet hole is normally indicative of a discharge of 12 to 18 inches or less.
The presence of scattered specks of unburned and partially burned powder grains without any accompanying soot is often observed at distances up to 25 inches (and occasionally as far as 36 inches).
More than 3 feet, will usually not deposit any powder residues, and the only visual indication is a dark ring around the hole, known as a bullet wipe.
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Gunpowder Residue When garments or other evidence relevant to a shooting
are received in the crime laboratory, the surfaces of all items are first examined microscopically for the presence of gunpowder residue.
Chemical tests, such as the Greiss test, may be needed to detect gunpowder residues that are not visible.
The firing distances involving shotguns must again be related to test firing.
The muzzle to target distances can be established by measuring the spread of the discharged shot.
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Primer Residue on Hands
The firing of a weapon not only propels residues toward the target, but gunpowder and primer residues are also blown back toward the shooter.
As a result, traces of these residues are often deposited on the firing hand of the shooter, and their detection can provide valuable information as to whether or not an individual has recently fired a weapon.
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Primer Residue on Hands Examiners measure the amount of barium and
antimony on the relevant portion of the suspect’s hands, such as the thumb web, the back of the hand, and the palm.
They may also characterize the morphology of particles containing these elements to determine whether or not a person has fired, handled a weapon, or was near a discharged firearm.
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Serial Numbers
Increasingly, the criminalist is requested to restore a serial number when it has been removed or obliterated by grinding, rifling, or punching.
Restoration of serial numbers is possible through chemical etching because the metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath the original numbers.
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Tool Marks A tool mark is considered to be any impression,
cut, gouge, or abrasion caused by a tool coming into contact with another object.
A careful examination of the impression can
reveal important class characteristics, such as the size and shape of the tool.
But it is the presence of any minute imperfections on a tool that imparts individuality to that tool.
The shape and pattern of such imperfections are further modified by damage and wear during the life of the tool.
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Tool Marks The comparison microscope is used to compare
crime-scene toolmarks with test impressions made with the suspect tool.
When practical, the entire object or the part of the
object bearing the tool mark should be submitted to the crime laboratory for examination.
Under no circumstances must the crime scene investigator attempt to fit the suspect tool into the tool mark. Any contact between the tool and the marked
surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence. 70
Other Impressions Impressions of other kinds, such as shoe, tire or
fabric impressions, may be important evidence.
Before any impression is moved or otherwise handled, it must be photographed (including a scale) to show all the observable details of the impression.
If the impression is on a readily recoverable item, such as glass, paper, or floor tile, the evidence is transported intact to the laboratory.
If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the print in a manner similar to lifting a fingerprint.
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Other Impressions
When shoe and tire marks are impressed into soft earth at a crime scene, their preservation is best accomplished by photography and casting.
In areas where a bloody footwear impression is very faint or where the subject has tracked through blood leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions.
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Points of Comparison A sufficient number of points of comparison or the
uniqueness of such points will support a finding that both the questioned and test impressions originated from one and only one source.
New computer software and web sites may be able to assist in making shoe print and tire impression comparisons.
Also, bite mark impressions on skin and foodstuffs have proven to be important evidence in a number of homicide and rape cases.
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The EndThe End
