Firearms and Toolmarks Flashcards

1
Q

semi-automatic vs automatic firearms

A

semi-automatic = trigger fires one bullet at a time
automatic = trigger continuously fires (like a machine gun)

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2
Q

fireformed vs non-fireformed impressions

A

fireformed = can only occur if gun is fired
non-fireformed = can occur by simply loading cartridge into firearm

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3
Q

what are examples of non-fireformed impressions

A

extractor impression, ejector mark, magazine mark

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4
Q

extractor vs ejector

A

extractor = removes cartridge case from the chamber
ejector = expels cartridge case from gun

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5
Q

handgun vs long gun

A

handgun = one hand, no other support needed
long gun = two hands, shoulder, etc.

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6
Q

revolver vs pistol

A

revolver = revolving chamber
pistol = stationary chamber

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7
Q

rifle vs shotgun

A

rifle = single projectile
shotgun = cluster of pellets (sprays)

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8
Q

bolt action vs lever action vs pump

A

bolt action = pull forward and back on top of gun
lever action = pull lever out by trigger
pump action = pull forward and back on bottom of gun

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9
Q

single vs double action

A

single action = pull slide/cock hammer manually each time
double action = trigger cocks hammer for you

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10
Q

what does barrel rifling do?

A

allows bullet to fire straight

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11
Q

what are some class characteristics of rifling?

A
  • caliber
  • twist (R or L)
  • number of lands or grooves
  • width of lands and grooves
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12
Q

which way do the machining marks run for grooves? what about lands?

A

grooves = length of barrel (across)
lands = axis of barrel (up and down)

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13
Q

how do you find the caliber of rifling?

A

distance between the lands

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14
Q

what does the cartridge case contain?

A

primer, propellant, and bullet

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15
Q

what are cartridge cases usually made of?

A

brass (also use steel or aluminum)

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16
Q

what is single base propellent made of?

A

nitrocellulose (wood pulp + nitric acid)

16
Q

what are primers usually made of?

A

barium, antimony, and lead

17
Q

what is double base propellent made of?

A

nitrocellulose and nitroglycerine

18
Q

what is the fastest/slowest propellant shape to burn?

A

fastest = flake/lamel
slowest = rod

19
Q

what is the firing sequence of a gun?

A

1) firing pin strikes primer
2) primer ignites; powder ignited by primer flame
3) burning powder forms gases
4) expanding gases propel projectile

20
Q

full metal jacket (FMJ) vs total metal jacket (TMJ) vs hollow point (HP)

A

FMJ = covers entire bullet; goes straight through
TMJ = covers entire bullet besides the base; straight through
HP = covers in ring pattern “hollow”; slows down; flattens and sometimes breaks apart

21
Q

what is a tool?

A

an object that is harder and/or has a mechanical advantage over another object

22
Q

compression vs striated vs cutting

A

compression = pressed straight into substrate (class not individual)
striated = harder item is slid laterally across (individual not class)
cutting = first compressed, then striated (both individual and class)

23
Q

what are some examples of compression tools?

A

hammers, pliers, chisels

24
Q

what are some examples of striated tools?

A

pry bars, screwdrivers, extrusion dies

25
Q

what are some examples of cutting tools?

A

bolt cutters, wire cutters, shears/snips

26
Q

class vs subclass

A

class = intentional by manufacturer
subclass = smaller group; not intentional

27
Q

what are some sources of individual characteristics on tools?

A
  • manufacturing imperfections
  • use/abuse
  • decay/corrosion
28
Q

what is forging?

A
  • type of forming manufacturing
  • pounding metal into shape
29
Q

what is stamping?

A
  • a type of forming manufacturing
  • sheets of metal pressed into shape and/or cut by being stamped between two surfaces
30
Q

what is shearing?

A
  • a type of cutting manufacturing
  • force applied between two surfaces that are offset
31
Q

lathe vs milling

A
  • a type of cutting manufacturing
  • lathe = for items with radial symmetry; spinning workpiece against stationary cutting tool
  • milling = for items without radial symmetry; spinning cutting tool against stationary workpiece
32
Q

what is a drill press?

A
  • a type of cutting manufacturing
  • drill bit rotates to create round holes
  • impressions only come from blind holes NOT through holes
  • size and shape of drill bit creates class characteristics
33
Q

what is broaching?

A
  • a type of cutting manufacturing
  • series of progressively smaller teeth that slowly cuts away small amounts of material
  • can be used to turn circular holes into more complex shapes
  • rarely need to be sharpened (creates subclass characteristics)
34
Q

what is a grinder?

A
  • used for finishing process
  • abrasive wheel used to remove material (can create extremely smooth finish)
  • grinding wheel consumed, so new grit particles are continually exposed
35
Q

what is shotblasting/sandblasting?

A
  • used for finishing process
  • randomly bombard material with sand particles or steel pellets
  • VERY individual
36
Q

what is extrustion?

A
  • pliable solid material is forced through an opening under pressure
  • material assumes shape of opening
  • materials in form of sheets, pipe, tubing, wire, and complex shapes
  • any substance that can be rendered molten through heat and pressure but quickly hardens after cooling (metals, polymers, glass)
37
Q

what are the factors affecting toolmarks?

A
  • tool angle
  • longitudinal angle
  • substrate hardness
  • pressure
  • directionality
  • path
  • wear/weathering
  • alteration