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

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Firearms (and a little Ballistics) When a gun barrel is manufactured, the rifling formula is registered with the FBI. Specific measurements would include: Depth ... – PowerPoint PPT presentation

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


1
Firearms (and a little Ballistics)
2
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?

3
  • 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.

4
  • 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.

5
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.

6
Got Firearms?
7
Got Firearms?
8
The Famous Polish Handgun
9
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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13
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.

14
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.

15
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.

16
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.

21
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.

22
Rifles
  • Rifles have a lever or a sliding bolt to eject a
    spent cartridge and bring the next one into the
    firing chamber.

23
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.

24
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?
27
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.

28
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.

29
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.

30
  • 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

31
  • 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.

32
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.

33
  • 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.

34
  • 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

35
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.

36
Comparison Microscope
  • This microscope has the ability to enlarge two
    objects at the same time and line them up side by
    side.

37
Comparison Microscope
38
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.

39
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.

40
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

41
Confirmatory tests
  • Chemical test color changing diphenylamine
    will turn blue in the presence of GSR

42
  • Tools used to find the angle of a bullets path

43
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)

44
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

45
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

46
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

47
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

48
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.
49
OK, OKready?. The Chinese invented.
50
Aside from gunpowder
  • Paper making
  • Printing
  • The compass
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