Ballistics and Explosives

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Ballistics and Explosives
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Ballistics

• The science of the motion of projectiles, such
  as bullets from a gun. It is divided into three
  branches
• interior ballistics,
• exterior ballistics,
• and terminal ballistics.

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3 Types of ballistics

• Interior ballistics studies the projectile in the
  gun while exterior ballistics studies the
  projectile in and through the air. Finally
  terminal ballistics is the study of penetration
  of solids by the projectile million (Silvia,
  1999. p. 69-70).

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History of ballistics

• Charles Waite considered father of forensic
  ballistics
• Opened private lab in New York City named The
  Bureau of Forensic Ballistics in 1927.
• Phillip Gravelle and John Fischer were his
  partners along with Dr. Calvin Goddard .

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Calvin Goddard

• In the late 1920s, the work of Calvin Goddard
  brought the FBI (formally named in 1932) even
  more fully into the application of science to
  detective work.  Goddard, a pioneer in forensic
  ballistics, was instrumental in the opening of
  the Scientific Crime Detection Laboratory, then
  affiliated with Northwestern University, in
  Chicago.  The Bureau learned much from Goddards
  lab and it supported many of the efforts made by
  this organization over the next several years.

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Bullets recovered from the bodies
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Goddard and his comparison microscope
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Modern Comparison Microscope
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The Bullet.
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Common types of rounds
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Proper Technique
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38 Caliber and 44 Caliber
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How a bullet is fired

• The bullet casing or shell is also marked or
  striated when it cycles through a gun.
• A firing pin striking the primer leaves a
  specific mark in the back of the shell
• Commonly, a semi- automatic or automatic firearm
  will eject the casing on its own immediately
  after being fired
• The mechanism that ejects the casings will also
  create its own striations on the shell.

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The Barrel rifling
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Rifling and Striations

• Many modern guns have rifling in their barrels
• The rifling adds spin to a bullet, causing it to
  travel straight.
• Because the bullet fits the barrel exactly, the
  rifling of the barrel leaves marks, or striations
  on the bullet.
• Since each gun is different, the marks a
  particular gun makes on a bullet shot through its
  barrel is unique, like a fingerprint.

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Striations

• Every gun leaves striations on every bullet and
  casing that travels through it.
• These striations are unique to each gun, no two
  are exactly alike.
• These striations are like fingerprints that can
  be compared and traced
• Obviously this is very helpful in identifying
  what weapon was used in a particular crime

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Lands and Grooves
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Comparison scope of lands and grooves match up.
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What must be collected

• Of course evidence must first be collected from
  the scene.
• Shell casings may be found on the ground near
  where the shooter was standing
• Bullets may be found lodged in surrounding items
  such as trees, walls, the ground, or they may be
  found still lodged in the victim.
• If possible the gun may even be uncovered at the
  scene.

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Compare their evidence

• The evidence must now be compared to other
  evidence.
• Bullets and casings can be compared to bullets
  and casings from other crimes or crime scenes
  using most often a microscope.
• If a weapon is found or seized, scientists can
  test fire the weapon and compare these new
  bullets and shells with bullets and shells from
  the original crime.

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Firing pin marks
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Comparison micrograph of firing pin marks
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Firing pin drag marks
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Extractor marks
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Ejector
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Exhibit 1 (cartridge case) could neither be
identified nor eliminated as having been fired by
Exhibit 2 (firearm).

• The above conclusion is reached if the cartridge
  case lacks sufficient action marks to be
  identified as having been fired by the questioned
  firearm or the firearm in question fails to
  produce reproducible individual characteristics
  on standards. 

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Exhibit 1 (cartridge case) could neither be
identified nor eliminated as having been fired by
Exhibit 2 (firearm).

• All general class characteristics such as caliber
  and firing pin shape would have to agree.  The
  image below shows a comparison between two
  cartridge cases that lack any individual
  characteristics but have a similar general
  appearance.

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Watertank
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Water tanks preserve the bullet

• In order to observe the striations in the
  bullets, scientists fire bullets into a tank of
  water.
• The water helps preserve the striations left on
  the bullet from the gun used.
• The scientist can then look at the bullet under a
  microscope and compare the striations to other
  bullets that have been used in a crime.

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Balistics Gelatin

• used by the shooting industry to simulate soft
  body tissue, Ballistic Gelatin provides an
  alternative to live animal or cadaver testing. 

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Exhibit 1 (cartridge case) was not fired by
Exhibit 2 (firearm).

• This conclusion can sometimes be reached when the
  submitted cartridge case exhibits very good
  individual characteristics that are very
  dissimilar to those produced on standards. 
• However, consideration must be given to the
  possibility that the firearm in question could
  have changed significantly. 
• If all dissimilarities can be accounted for, a
  negative conclusion will be reached.  The
  comparison image below shows two cartridge cases
  that exhibit noticeably different breech marks
  and firing pin impressions.

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Striae
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The survey says

• Based on the results of these tests, scientists
  can now prove or disprove weather or not two
  bullets were fired from the same gun, or weather
  or not a gun fired a certain bullet.
• This crucial evidence can often make or break a
  case in court, so long as it is presented in the
  right manner

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Possible Problems of Ballistics

• Shotguns and revolvers
• Bullet expansion and deformation
• No two bullets are EVER the same
• Barrels, along with the whole firearm can be
  altered, switched, or destroyed.

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Striations
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Striations Lands and Grooves
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Types of bullets

• A full metal jacket bullet is a bullet encased in
  a copper alloy.
• A hollow point bullet is a bullet that has a
  hollowed out shape in its tip.
• A frangible bullet is designed to disintegrate
  into tiny particles upon impact to minimize their
  penetration.
• A rubber bullet and plastic bullet are designed
  to be non-lethal, and are used in situations such
  as riot control.

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Civil war bullets

• Round projectiles not accurate past a short
  distance. Gasses blowing by the round sice it was
  not a snug fit. To remedy this a cloth was added
  around the round to make up any gap that existed.

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Links

• http//www.youtube.com/watch?vtTHo0K2Sc0g
• http//www.youtube.com/watch?vQ7w4M-LNXuQfeature
  endscreen
• http//www.youtube.com/watch?v_eUlpPY96Ok
• http//www.youtube.com/watch?v65cNVA_OCtE

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Cavitation
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Shotgun Slug vs. Shot
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Bullet in body X-Ray
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Summary of wound types
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General Features of Entrance Wounds

• A dirt ring around the wound caused by the bullet
  'cleaning' itself off on the skin as it passes
  through fibers may be found in the wound from
  clothing covering the wound a smaller defect than
  the diameter of the bullet due to elastic recoil
  of the skin.
• Powder blackening may indicate direction of fire
  (ex. a circular zone of blackening from a shot
  fired at right angles to the skin surface,
  compared to an oblique zone from an oblique shot
  etc) stippling/ tattooing of the skin charring of
  the skin entry wounds caused by shots fired at a
  distance.
• Entrance wounds into skull bone typically
  produces beveling, or coning, of the bone at the
  surface away from the weapon on the inner table.
  In thin areas such as the temple, this may not be
  observed. Sternum, iliac crest, scapula, or rib
  may show similar features. 

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General Features of Entrance Wounds

• Tangential entrance wounds into bone may produce
  "keyhole" defects with entrance and exit
  side-by-side, so that the arrangement of beveling
  can be used to determine the direction of fire. 
• Use of silencers (or "muzzle brakes" to deflect
  gas and recoil) may produce atypical entrance
  wounds. A silencer is a device, often homemade,
  fitting over the muzzle that attempts to reduce
  noise by baffling the rapid escape of gases.
  Entrance wounds may appear atypical at close
  range.

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General Features of Exit Wounds

• A larger wound than the entrance wound, due to
  the bullet tumbling in it's passage through the
  body, and bony fragments being forced out through
  the skin can be of any size or shape, but are
  usually irregular (slit-like or square). May be
  similar to the entrance wound in size if the
  bullet was fired from a high velocity rifle shot
  at long distance (ex. a military rifle) a
  'shored' exit wound occurs where the wound edges
  are abraded against an overlying object pressed
  firmly against the skin, as the skin is pushed
  out from the body by the bullet. The features
  were directly proportional to the KE of the
  projectile and the rigidity of the shoring
  material.
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X-ray of .38 to skull
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X-Ray of shotgun pellets to abdomen
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CT of head showing boney fragments pushed in to
brain area
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9mm semi automatic
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Revolver
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Firearm Anatomy
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Firearm Anatomy
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Semi-auto rifle
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Handgun vs. rifle bullet
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Bullets after striking a target
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Handgun Caliber

• Caliber is used to describe the size of a rifle
  or handgun bore and the size of cartridges
  designed for different bores. Caliber is usually
  measured as the diameter of the bore from land to
  opposite land and is expressed in hundredths of
  an inch, thousandths of an inch, or millimeters.
  For example, a .270-caliber rifle bore measures
  270/1000ths of an inch in diameter between the
  lands and has a larger bore diameter than a
  .223-caliber rifle. However, there is no standard
  set for designating caliber. In some cases, the
  caliber is given as the diameter of the bullet,
  which is the distance between the grooves.
  Caliber designations sometimes have a second
  number that has nothing to do with the diameter.
  For example, the popular .30-30 is a .30-caliber
  cartridge, but the second number is a holdover
  from the days when the cartridge took 30 grains
  of powder. The "06" in .30-06 refers to the year
  (1906) it became the official ammunition of the
  U.S. military. Circles show bore sizes of common
  cartridges. Having the same bore size does not
  mean different cartridges are interchangeable.

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Handgun Caliber

• Every rifle or handgun is designed for a specific
  cartridge. The ammunition must match the data
  stamp on the firearm. For example, there are
  several .30-caliber firearms that use the same
  bullet size but are designed for different
  cartridges (the .30-30, .30-06, .308, and the
  .300 Savage). If you cannot find the caliber
  stamped on the firearm, take it to a qualified
  gunsmith.

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Handgun Caliber picture
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Shotgun Gauge

• Shotgun gauges are determined by the number of
  lead balls of a given diameter required to make
  one pound of that size ball. Thus 10 balls of 10
  gauge diameter are required to make one pound of
  such balls, or 20 balls of 20 gauge diameter are
  required to make one pound, and so forth.

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Gauge sizing
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Shotgun Parts
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Choke types To control spread and impact point of
shot
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Shot Shell
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Miscellaneous Ammo

• Breaching rounds - Shotguns are commonly used in
  the military to "unlock" doors when troops don't
  know what lies on the other side. Because
  traditional ammo tends to ricochet and may end up
  hitting the shooter or someone inside the room,
  breakable "breaching rounds" are often used.
  These shells contain a metallic powder that
  disperses on contact.
• Bean bags - Bean bags are used as shotgun ammo in
  crowd control situations, as in most cases they
  stun the victim but do not inflict lasting
  damage.
• CS gas grenades - Combat shotguns can be used to
  disperse tear gas and similar chemicals.
• Rock salt - Rock salt is a popular home defense
  ammunition because it reportedly causes severe
  pain but usually no permanent damage.

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Alternative shotgun shells
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Shotgun Shot (pellet) sizing
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Shotgun Gauge Comparison Video

• http//www.youtube.com/watch?vBXz_Aftj8rEfeature
  related