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forensic chemistry > firearms > Flashcards

firearms Flashcards

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1
Q

what is a magazine

A

it holds several cartridges of ammunition

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2
Q

how do firearms work

A

the cartridge is loaded in the firing chamber. the firing pin in the chamber strikes and ignites the primer which, in turn, ignites the gunpowder

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3
Q

what component is on the top of the bullet

A

bullet

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4
Q

what component is inside of the bullet

A

propellant

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5
Q

what component is surrounding the bullet

A

casing

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6
Q

what component is surrounding the bottom of the bullet

A

rim

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7
Q

what component is directly at the bottom of the bullet

A

primer

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8
Q

what are shotguns

A
  1. smooth barrel
  2. has pellet or small lead ball ammunition
  3. gauge: describes the diameter of the shotgun barrel
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9
Q

firearms manufacturing: what are the impressions in the inner surface of the barrel

A
  • grooves: spiral impressions cut or impressed into the inner surface of the barrel
  • lands: the remaining surfaces produced by the original drill bore
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10
Q

firearms manufacturing: what are buttons

A
  • a type of broach
  • contain the groove pattern which is impressed onto the barrel or passed through the barrel using high pressure
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11
Q

firearms manufacturing: what are cutters

A
  • a type of broach
  • concentric steel rings that were used in the production of pre-1940 weapons
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12
Q

what are the individual characteristics of firearms

A
  • metal fragments impressed at random into the metal in the barrel manufacture process
  • wear and tear from use and improper cleaning
  • micro grooving features
  • ejector and extraction markings
    longitudinal striations
    scratches
  • nicks
  • abrasion
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13
Q

how to handle a weapon before unloading

A
  1. hold at the edge of the trigger guard or the checkered portions of the grip
  2. tag the weapon on the trigger guard
  3. record the chambers containing the cartridges and their positions
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14
Q

what are firearms test fires

A

it is a method used to compare an evidence bullet with a bullet from their ammunition case that has been fired with a weapon in question that may have been used in a crime

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15
Q

how to do a comparison microscopy of firearms/stereomicroscopy

A
  • as bullets pass through the barrel, its surface is cast with impressions of the rifled markings, grooves, twist, striations and wear characteristics of the weapon
  • evidence and test fire bullets and cartridge cases can be examined simultaneously in the same field of view using a comparison microscope
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16
Q

what are the impressions on fired ammunition

A
  • a trigger pull causes the firing pin to release and strike the primer in the primer cup of the cartridge case
  • the ignition of the primer causes the gunpowder in the primer cup to ignite
  • the burning gases propel the bullet forward while the cartridge case is pushed backward against the breechblock
  • the firing pin marking may be centered, off-center or distorted and striations and impressions associated with its contact with the cartridge case can be individualizing
  • the cartridge case may also be impressed with markings from the surface of the breechblock including machining imperfections
  • extractor markings from removing the cartridge from the firing chamber
  • ejector markings may be present from this mechanism used to eject, or throw, the spend cartridge case from the firearm
17
Q

what is an integrated ballistic identification system (IBIS)

A
  • automated firearms search system
  • firearms database, comparison and image retrieval tools
  • networked labs can share firearms examination casework and comparison data by attached a video camera/microscope camera
18
Q

what is gunshot reside (GSR)

A
  • nitrocellulose-containing smokeless powder that produces gases upon ignition that propel the bullet forward
  • after the weapon is fired, traces of GSR and unburned smokeless powder are often recovered from the shooter, victim and / or target surface
19
Q

fire patterns: d=12-18” (inches)

A

when fabric is present, the fibers around the hole are burned. If the weapon is fired at a distance of 12-18”, a smoke halo stippling of GSR will be present on the target

20
Q

fire patterns: d=25-36”

A

at a distance of 25-36”, unburned gunpowder residues can be found on the target in the form of scattered specks but no pattern

21
Q

fire patterns: d= >36”

A

at distances greater than 36”, no powder residue will be recovered but a bullet wipe, or dark ring around the hole, will be present

22
Q

how to analyze gunshot residue

A
  • partially burned and unburned gunpowder particles may be recovered both from the target and the shooter. GSR can be recovered from the hands of suspects who recently fired a weapon (less than two hours from the time of fire), victims and other targets by swabbing or through the use of adhesive disks that captures the gunpowder and gunshot residue
  • sampling the thumb web, palm and back of the suspect’s hand can help to determine if a suspect has recently fired, handled, or was near a recently fired weapon
  • fabrics and surfaces of items receiving the bullet are examined using an infrared light and microscope to locate any traces of gunpowder residue
23
Q

gunshot residue analysis: griess test

A
  • nitrites can be used to tentatively identify gunpowder residue
  • pink
24
Q

gunshot residue analysis: dermal nitrate test

A
  • for the presence of unburned nitrates using diphenylamine
  • blue
25
Q

what is SEM-EDS of primer residue

A
  • SEM can be used to identify GSR by the characteristic size and shape of the particles
  • the EDX attachment is used to perform an elemental analysis of the GSR residue and can identify barium, lead and antimony present in the sample
  • atomic absorption spectroscopy and neutron activation analysis can also be used to analyze the elemental composition and primer residue on evidence.

forensic chemistry (2 decks)

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