Firearms and Toolmarks

Question 1

semi-automatic vs automatic firearms

Answer 1

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

Question 2

fireformed vs non-fireformed impressions

Answer 2

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

Question 3

what are examples of non-fireformed impressions

Answer 3

extractor impression, ejector mark, magazine mark

Question 4

extractor vs ejector

Answer 4

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

Question 5

handgun vs long gun

Answer 5

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

Question 6

revolver vs pistol

Answer 6

revolver = revolving chamber
pistol = stationary chamber

Question 7

rifle vs shotgun

Answer 7

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

Question 8

bolt action vs lever action vs pump

Answer 8

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

Question 9

single vs double action

Answer 9

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

Question 10

what does barrel rifling do?

Answer 10

allows bullet to fire straight

Question 11

what are some class characteristics of rifling?

Answer 11

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

Question 12

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

Answer 12

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

Question 13

how do you find the caliber of rifling?

Answer 13

distance between the lands

Question 14

what does the cartridge case contain?

Answer 14

primer, propellant, and bullet

Question 15

what are cartridge cases usually made of?

Answer 15

brass (also use steel or aluminum)

Question 16

what is single base propellent made of?

Answer 16

nitrocellulose (wood pulp + nitric acid)

Question 16

what are primers usually made of?

Answer 16

barium, antimony, and lead

Question 17

what is double base propellent made of?

Answer 17

nitrocellulose and nitroglycerine

Question 18

what is the fastest/slowest propellant shape to burn?

Answer 18

fastest = flake/lamel
slowest = rod

Question 19

what is the firing sequence of a gun?

Answer 19

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

Question 20

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

Answer 20

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

Question 21

what is a tool?

Answer 21

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

Question 22

compression vs striated vs cutting

Answer 22

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)

Question 23

what are some examples of compression tools?

Answer 23

hammers, pliers, chisels

Question 24

what are some examples of striated tools?

Answer 24

pry bars, screwdrivers, extrusion dies

Question 25

what are some examples of cutting tools?

Answer 25

bolt cutters, wire cutters, shears/snips

Question 26

class vs subclass

Answer 26

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

Question 27

what are some sources of individual characteristics on tools?

Answer 27

- manufacturing imperfections - use/abuse - decay/corrosion

Question 28

what is forging?

Answer 28

- type of forming manufacturing - pounding metal into shape

Question 29

what is stamping?

Answer 29

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

Question 30

what is shearing?

Answer 30

- a type of cutting manufacturing - force applied between two surfaces that are offset

Question 31

lathe vs milling

Answer 31

- 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

Question 32

what is a drill press?

Answer 32

- 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

Question 33

what is broaching?

Answer 33

- 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)

Question 34

what is a grinder?

Answer 34

- 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

Question 35

what is shotblasting/sandblasting?

Answer 35

- used for finishing process - randomly bombard material with sand particles or steel pellets - VERY individual

Question 36

what is extrustion?

Answer 36

- 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)

Question 37

what are the factors affecting toolmarks?

Answer 37

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