l8 Forensic Chemistry; Firearms and Toolmarks

Question 1

firearms identification

Answer 1

A discipline mainly concerned with
determining whether a bullet or
cartridge was fired by a particular
weapon; it is not to be confused
with ballistics, which is the study of
a projectile in motion.

Question 2

grooves

Answer 2

The cut or low-lying portions between the lands in a rifled bore.

Question 3

rifling

Answer 3

The spiral grooves formed in the bore of a firearm barrel that impart spin to the projectile when it is fired.

Question 4

bore

Answer 4

The interior of a firearm barrel.

Question 5

lands

Answer 5

The raised portion between the grooves in a rifled bore.

Question 6

caliber

Answer 6

The diameter of the bore of a
rifled firearm; the caliber is usually
expressed in hundredths of an inch
or millimeters—for example, .22
caliber and 9 mm.

Question 7

gauge

Answer 7

Size designation of a shotgun,
originally the number of lead balls
with the same diameter as the
barrel that would make a pound;
for example, a 12-gauge shotgun
would have a bore diameter of a
lead ball 1/12 pound in weight; the
only exception is the .410 shotgun,
in which bore size is 0.41 inch.

Question 8

breechface

Answer 8

The rear part of a firearm barrel.

Question 9

extractor

Answer 9

The mechanism in a firearm by
which a cartridge of a fired case is
withdrawn from the chamber.

Question 10

ejector

Answer 10

The mechanism in a firearm that
throws the fired cartridge case
from the firearm.

Question 11

distance determination

Answer 11

The process of determining the distance between the firearm and a target is usually based on the distribution of powder patterns or the spread of a shot pattern.

Question 12

choke

Answer 12

An interior constriction placed at or
near the muzzle end of a shotgun’s
barrel to control shot dispersion

Question 13

Greiss test

Answer 13

A chemical test used to develop patterns of gunpowder residues
around bullet holes.

Question 14

what is a tool mark?

Answer 14

Any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object

Question 15

careful examination of a tool mark impression can reveal..? and the presence of minute imperfections can..?

Answer 15

important class characteristics, impart individuality

Question 16

what are 4 common tasks of a forensic firearms laboratory?

Answer 16

1. Comparison of bullets and casings
2. Detection and characterization of gunpowder residues
   -Garments, wounds, and hands
3. Estimation of muzzle-to-target distances
4. Restoration of obliterated serial numbers on weapons

Question 17

briefly describe handguns

Answer 17

-designed to be fired with one hand
-common types: single shot, revolver and semi-auto
-can be single-action or double-action

Question 18

briefly describe long guns

Answer 18

-Designed to be fired while resting on the shoulder
-Can be single-shot, repeating, semi-automatic, or automatic
-shotguns and rifles

Question 19

briefly describe shotguns

Answer 19

-smooth barrels
-Shell ammunition contains numerous ball-shaped projectiles called shot

Question 20

briefly describe rifles

Answer 20

-barrels have lands and grooves
-Bullet ammunition is impressed with lands and grooves during firing

Question 21

list 4 parts of a gun that can leave ‘toolmarks’ on a bullet when fired

Answer 21

-barrel
-firing pin
-breechface
-ejector

Question 22

explain class characteristics of a gun

Answer 22

markings are peculiar to a particular type of gun

Question 23

explain how individual characteristics of a gun can be used to link suspects to crime

Answer 23

-bullet acquires features of the barrel as it is fired

If one bullet at the scene of a crime and another test-fired from a suspect’s gun show the same markings

–the suspect is linked to the crime

Question 24

what is the main source of both class and individual evidence of a gun?

Answer 24

the barrel

Question 25

list type and examples of characteristics from the rifling method?

Answer 25

defines class characteristics of a barrel - # of lands and grooves - width (caliber) - direction of twist (left or right handed)

Question 26

explain striations of a gun?

Answer 26

-fine lines found in the interior of the barrel due to imperfections in rifling methods, Imparted on a bullet as it passes through -microscopic and randomly irregular -unique to each barrel -form individual characteristics

Question 27

what is true of striations?

Answer 27

No two rifled barrels, even those manufactured in succession, have identical striation markings

Question 28

how are bullet markings compared?

Answer 28

-examiner must obtain “test bullets” fired through the suspect barrel for comparison -Initial stages of examination look at class characteristics -Any differences at this stage will exclude this barrel -same class characteristics, move onto matching striations with a comparison microscope

Question 29

3 things that exit a firearm when fired

Answer 29

-Bullet -Smoke -Unburned and partially burned gunpowder

Question 30

what allows for distance determination?

Answer 30

distribution of gunpowder particles and other discharge residues around a bullet hole

Question 31

how can an examiner assess distance?

Answer 31

comparison of powder-residue patterns from: -Patterns on victim’s clothing or skin -Test patterns generated from suspect weapon

Question 32

how can we determine whether or not an individual has recently fired a weapon?

Answer 32

-Gunpowder and primer residues are also blown back toward the shooter -often on the firing hand -detection of residues can provide info