Firearms%20(and%20a%20little%20Ballistics)

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Firearms (and a little Ballistics)
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Once upon a time...more than 1000 years ago

• the Chinese discovered black powder.
• Black powder, (gunpowder or smokeless powder)
  was considered one of the Four Great Inventions
  of the Chinese. Do you know the other 3?

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• Anyway, it wasnt until the 14th century, that
  gunpowder was used in guns.
• The first guns were cannons large fixed, metal
  devices that were better at making noise than
  anything else.

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• Eventually cannons became more accurate and
  useful and the idea of pushing a projectile out
  of a metal barrel using gunpowder became part of
  modern warfare.
• The next big step in the evolution of firearms
  occurred when cannons were made small enough for
  one person to handle.

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One hand or two?

• Guns that needed 2 hands were called long guns.
• Guns that needed only one hand were called hand
  guns.
• Seems to make sense.

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Got Firearms?
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Got Firearms?
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The Famous Polish Handgun
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Where do we stand now with guns?

• If you watch TV you will see guns everywhere.
  Old Westerns, gang movies, police shows, good guy
  vs. bad guy stuff you know what I mean.
• In reality, guns are commonly used in criminal
  activity. Murder or injury is a common reason to
  shoot someone but many times a gun is merely used
  to gain control over a situation. Having a gun
  used in armed robberies, abductions, or rape can
  convince any victim to comply.

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• Deaths from gunshots can be accidental,
  suicidal, or homicidal. In homicide, evidence
  from the gun or ammunition often proves to be the
  perpetrator's undoing.
• So, how does a gun or bullet give a perpetrator
  away?

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Firearms Identification

• A discipline mainly concerned with determining
  whether a bullet or cartridge was fired by a
  particular weapon.
• Not to be confused with ballistics, which is the
  study of a projectile in motion.

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Firearms examiners also do ballistics.

• Examiners commonly have to
• Analyze bullets and shell casings found at a
  crime scene to determine what type of weapon
  fired them
• Help with crime-scene reconstruction by
  estimating the distance between the gun muzzle
  and the victim or by working out the trajectory
  of the bullets.
• Match a bullet or shell casing to a particular
  weapon or to a sample from a different crime
  scene to link the two.

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How do guns work?

• Basically, guns work by starting an explosion
  that sends a bullet racing out of the barrel.
  When you pull the trigger of a gun, its firing
  pin strikes a cylinder of the primer in the shell
  of the bullet and ignites it, causing the
  gunpowder in the shell to explode. The explosion
  pushes the bullet through and out of the guns
  barrel.

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Guns are classified into 3 categories

• Handguns
• Rifles
• Shotguns

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Handguns

• There are three basic types
• Revolvers You see these in old westerns. They
  have that revolving cylinder thingy holding the
  cartridges. It fires once with each trigger
  pull.
• Semiautomatic pistols The magazine or clip is
  spring loaded holding a stack of cartridges. It
  fires once with each trigger pull.
• Machine pistols The pistol fires repeatedly as
  long as you hold the trigger down.

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• Here is a picture of the interior of a
  semiautomatic handgun.

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Did you know.

• Early handguns were first invented in Pistoja, a
  town in Tuscany, Italy. These were very ornately
  decorated dueling handguns often having the name
  of the town inscribed on them. This is where we
  get the name pistol for a handgun.

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Rifles

• Rifles have a lever or a sliding bolt to eject a
  spent cartridge and bring the next one into the
  firing chamber.

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Shotguns

• Shotguns dont fire bullets but rather shells
  filled with groups of pellets (shot). As the
  shot exit the barrel, they spread out in a
  circular pattern which means shotguns dont
  require much aiming. Just point in the intended
  direction.

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So, what does it mean by the term caliber or
gauge?

• The caliber of a weapon is a measurement of the
  internal diameter of its barrel.
• Example A .38 caliber handgun has a barrel
  with a 0.38 inch barrel.
• The gauge of a shotgun is determined by counting
  the number of lead balls (matching the barrels
  diameter) that it would take to weigh one pound.
• Example Twenty lead balls the diameter of a 20
  gauge shotgun barrel weigh one pound.

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So, what were the other 3 great Chinese
inventions?
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Getting Info from the Ammo

• Nowadays investigators rarely find a gun at a
  crime scene criminals are getting smarter.
  Bullets found, however, can lead to the type of
  gun and even the individual gun used.
• During the collection and handling of any
  crime-scene bullets, the investigator must take
  great care not to damage or alter them.even when
  a ME takes a bullet out of a body during an
  autopsy.

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Trace evidence

• Bullets can have important trace evidence
  attached. Paint, fibers, and other materials
  may cling to the bullet as it passes through or
  ricochets off walls, doors, bricks or window
  screens. Sometimes small bits of flesh and blood
  found on a bullet can yield great DNA evidence.

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Shell casings

• A shell casing is the part of the cartridge that
  remains after the powder explodes and the bullet
  is gone. They really take a beating but this is
  good news. The more marks found on them, the
  more info they reveal.
• So, what can they tell you.

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• Firing pin impressions - The casing shows where a
  firing pin struck revealing whether the shell had
  a primer cup (a center-fire) or had a primer
  around the rim (rim-fire)
• Breechblock patterns When the powder in the
  casing detonates, it pushes the shell backwards
  against the breechblock leaving an impression

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• Headstamps Cartridge manufacturers stamp info
  onto the casing
• Extractor and ejector marks These are marks
  etched into the casing which come from automatic
  and semiautomatic weapons which seat the bullet
  into place or eject it from the weapon. They
  leave unique scratches on the sides of the shell
  casings.

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Rifling

• A spinning bullet is more accurate than a bullet
  that does not spin. Spinning objects that are
  propelled forward tend to go more in a straight
  line. (You knowjust like spinning football.)
• So, a most guns are rifled (have spiral grooves
  in the barrel) to make bullets spin as they
  leave.

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• Rifling consists of lands and grooves. The high
  parts are the lands and the deep cut-in parts are
  the grooves. This is a cross section of lands
  and grooves.
• This is a bullet with rifling markings. You can
  see the lands and grooves.

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• When a gun barrel is manufactured, the rifling
  formula is registered with the FBI. Specific
  measurements would include
• Depth of the groove
• Width of the lands
• Degree of twist
• Clockwise twist or counterclockwise twist
• Number of grooves

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Striations

• When lands and grooves grab and spin a bullet,
  they leave markings down the side of the bullet.
  They are linear and parallel to the long axis of
  the bullet. These striations are the heart of
  firearms identification.

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Comparison Microscope

• This microscope has the ability to enlarge two
  objects at the same time and line them up side by
  side.

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Comparison Microscope
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Databases

• IBIS Integrated Bullet Identification System .
  Records all bullets/casings inspected from any
  crime scene
• DRUGFIRE focuses more on shell casings but also
  contains bullet striation patterns
• NIBIN National Integrated Ballistics
  Information Network All scanned bullets and
  casing from a comparison microscope are stored in
  here.

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GSR

• When a gun is fired much of the explosive gases
  and matter dont completely follow the bullet
  down the barrel. Some materials escape through
  openings in the weapon. The chemical and
  particles of these gases, called gunshot residue
  (GSR) clings onto the shooters hand, arm
  clothing, face, nearby walls furniture, victim,
  etc basically anywhere near the shooter.

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GSR Presumptive tests

• Infrared photography
• The Griess test a filter paper test which when
  pressed over the area is then immersed in a
  reagent revealing GSR patterns

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Confirmatory tests

• Chemical test color changing diphenylamine
  will turn blue in the presence of GSR

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• Tools used to find the angle of a bullets path

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So, what things can you learn from a GSW?

• A gunshot wound (GSW) depends on certain
  factors
• the distance between the muzzle of a gun and the
  victim
• The caliber and velocity of the bullet
• The angle of entry
• Whether the bullet remained within the victim or
  passed through completely exiting the body (a
  through-and-through gunshot wound)

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Distance from muzzle to victim

• A. 2 ft away . small hole abrasion collar
  some black smudging may occur because the skin
  wipes the bullet clean

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Distance from muzzle to victim

• B. Between 6 and 2 feet skin is tattooed or
  stippled tiny gun powder particles are embedded
  in the skincausing hemorrhages (red dots or
  blood) a speckled pattern

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Distance from muzzle to victim

• C. 6 produces a hole, a compact area of
  stippling a surrounding area of charring a
  bright red hue to the wound tissue

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Distance from muzzle to victim

• D. If the muzzle is pressed against the victim
  when fired hot gases and matter are driven
  directly into the skin greater charring ripping
  of the skin in a star shape or stellate pattern

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Exit wounds are larger than entry wounds because
the bullet cuts and tears the tissue as it forces
its way through the body.Believe it or not, the
way a bullet effects the skin depends on what the
victim is wearing.
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OK, OKready?. The Chinese invented.
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Aside from gunpowder

• Paper making
• Printing
• The compass