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Firearms and Toolmark Examinations

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chichi's version from 2016-10-27 14:22

Section 1

Question Answer
Striationsare caused by movement across two surfaces
impressionsare stamps caused by expansion that led to contact between surfaces
firing marksonly be left behind if weapon is fired
cycling marksare caused by loading and unloading weapon
identification/exclusionpositively conclude that bullet or casing was or was not fired by a particular firearm
inconclusivethere are not sufficient individual microscopic features needed for bullet and casing comparison
unsuitablecondition of firearm is not suitable for comparison
cycledunfired ammunition has been worked through the action of specific firearm
memorize

Section 2

Question Answer
casinghouses powder, primer, and projectile
bulletprojectile that leaves barrel when gun is fired and hits target
powderignites and propels bullet through barrel
primerpressure sensitive compound that ignites powder
riflingcauses the bullet to spin for better accuracy
leftclockwise
rightcounterclockwise
by examining the bullet, examiners can determinenumber of land and grooves; their width; direction of twist
most striation comparisons are done by examining _____________bullet groove
class characteristictype of breech face pattern
individual characteristicgrooves within overall pattern
firing pin drag mark ____ on soft material of primersoft
firing marknot seen with just cycling
memorize

Section 3

Question Answer
ejector markused to punch out the extracted casing
flat (horizontal) firing pin markdrag mark at 3 o'clock position
IBISIntegrated Ballistic Identification System
NIBINNational Integrated Ballistic Information Network
Harder surface leaves marking on ___________softer surface
Gross operationsreduces raw metal to intermediate form
Fine operationscreates final dimensions, with the exception of parts requiring hand fitting
IBIStechnology that compares
NIBINnetwork of all IBIS; record of breech face and firing pin marks
memorize

Section 4

Question Answer
broachgang broach is twisted and pulled thru barrel
hooksingle cutting surface is rotated thru barrel; repeated for each groove
button swagepushing or pulling harder metal through barrel to displace metal and create rifling
electrochemical riflingcontact with electrode eats away metal
cation riflingacid etching that needs to be neutralized when complete
hammer forgedreverse image is hammered by setting barrel on reusable mandrel
memorize