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semiautomatic pistol
requires a separate pull of the trigger for each shot
uses energy of discharge to perform a portion of the operating or firing cycle
Pistol nomenclature
slide
barrel
extractor
hammer
breechface
firing pin aperture
extractor
revolver
rotating cylinder with chambers
can be discharged successively by the same firing mechanism
revolver nomenclature
cylinder
hammer
barrel
breechface
firing pin
Ammunition
headstamp - numerals, letters and symbols stamped into the head of the cartridge case
identifies the manufacturer, caliber, gauge or give additional information
Centerfire ammunition
cartridge (unfired)
bullet
gun powder
cartridge case
primer
types of bullets/characteristics
semi-jacketed soft point - soft lead core exposed at the nose
cannelure - a circumferential grove generally of a knurled or plain appearance (bullet or cartridge case)
Types of Bullets
full metal jacket
total metal jacket
semi-jacketed hollow point
lead round nose
semi wadcutter
wadcutter
full metal jacket
The bullet jacket encloses the entire bullet, except the base
total metal jacket
fully encases, including base
semi-jacketed hollow point
jacket, typically copper, surrounding the lower portion. lead nose of the bullet has a hollow point
lead round nose
an elongated projectile made of a lead alloy with a rounded nose
semi-wadcutter
designed with a truncated nose and a sharp shoulder
wadcutter
cylindrical with the sharp-shouldered nose intended to cut target paper cleanly to facilitate easy and accurate scoring
class characteristics
all discernable class characteristics are measurable
nominal caliber - diameter
number of land and groove impressions
width of the land and groove impression
direction of twist
damaged bullets
How can we determine the number of land/groove impressions if not all are visible
If you know the circumference and can measure a land and a groove impression, Circumference/distance across one land and groove impression
How can we determine the diameter if the bullet is misshapen?
detemine the # of land/groove impressions
calculate the C
remember C = (pi)diameter - C/pi =d
Rifling
Grooves are cut in a spiral pattern
between the grooves are raised areas called lands
Types of riflling
conventional
produces rifling with sharp edges
made by a broach cutter or button
polygonal rifling
produced with hammer forging
marks are not well defined
Bullet comparison
once a class characterisics are established, individual characteristics are evaluated
individual characteristics are unique marks
these marks cause striations and other imperfections used for comparison purposes
agreement of class characteristics - if are different, no further comparison
agreement of individual characteristics
Comparison microscope
allows viewing of two items simultaneously
magnification is typically adjustable from 4X to 40X magnification
cartridge case comparison
evaluation of class markings
breech face marks
firing pin impressions
extractor marks
ejector marks
chamber marks
parallel breechface marks
parallel marks from the breechface transferred to the cartridge case
other kinds of breechface marks include:
circuler
arched
breechface comparison
using a comparison microscope, both cartridge cases can be viewed simultaneously
firing pin impressions
firing pins have different shapes = different markings on cartridges
class shapes
elliptical
rectangular
hemispherical
circular
extractor marks
the extractor - metal hook
pulls the cartridge case from the chamber of the barrel after firing
markings both on and inside the rim of the cartridge case
can be uniquely identified to a particular extractor
Ejector marks
designed to eject the fired cartridge case'
The ejector comes in contact with the cartridge as the slide moves rearward
When the ejector hits the cartridge, it is kicked from the slide and out of the firearm
the contact between the cartridge case and the ejector results in an ejector mark
Ejection port marks
tornado marks
seen in Glock pistols, among others
Chamber marks
caused by imperfections in the barrel chamber
passed on to the cartridge case when it expands and is removed
can also be identified to a particular chamber