Firearm Identification
Laboratory Exercises
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Exercise #1: Measuring the Class Characteristics
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All of the measurements
we will be doing require
the use of vernier calipers
Calipers are used to
measure small distances
within .05 of a millimeter.
All measurements are to
be measured in
millimeters then
converted to inches for
use in the exercises.
Measuring the Class Characteristics
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Caliber
Number of Lands/Grooves
Direction of Twist
Width of Lands/Grooves
Measuring Caliber
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Using a vernier caliper,
measure the base of the bullet
to the hundredths of a
millimeter.
This bullet measures 11.50
millimeters
Multiply millimeters by
0.0394 to determine inch
measurement
11.5 x 0.0394 = .453 (approx.
.45 inches)
Record your results
11
.50
Types of Rifling
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Rifling is classified
as being either
“Cut” or “Polygonal”
Polygonal (P) rifling
has a smooth
transition between
lands and grooves
Cut (C) rifling has
defined shoulders
Polygonal Rifling
Cut Rifling
Counting the Lands and Grooves
The grooves of the
bullet are counted
It may be necessary
to place a small mark
with a felt tip pen in
the location where
counting begins.
1
2
3
Direction of Twist
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The twist is determined by sitting the bullet on
a flat surface and observing the direction of the
rifling.
Left
Right
Width of the Lands and Grooves
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Calipers are used to
measure the width of
the bullet lands and
grooves
Weighing the bullet
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The bullet weight is
recorded in grams
Convert the weight from
grams to grains
1 gram = 15.43 grains
Bullet Type
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Using the bullet
diameter, weight, and
construction
characteristics,
determine the bullet
type.
Exercise #2: Determining the Possible Make
of Firearm Based on Class Characteristics
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Using the
measurements of the
class characteristics, a
list of possible makes
of firearms can be
established
Exercise #2: Determining the Possible Make
of Firearm Based on Class Characteristics
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Use the appropriate
GRC (General Rifling
Characteristics) chart
based on the bullet
type being examined
(9mm, .38/.357, .40,
etc)
Exercise #2: Determining the Possible Make
of Firearm Based on Class Characteristics
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Use the rifling type
in this column for
determining type
of firearm
Exercise #2: Determining the Possible Make
of Firearm Based on Class Characteristics
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Next we use the
number of
lands/grooves and
direction of twist in
evaluating possible
makes of firearm
Exercise #2: Determining the Possible Make
of Firearm Based on Class Characteristics
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The last step of determining the
possible make of firearm is to
use the bullet land and groove
width
When using the GRC chart,
remember that the bullet groove
that you measured was made by
the barrel land. Therefore, use
the data from your bullet
groove in the LAND column.
The bullet land was produced
by the barrel groove and should
be used in the GROOVE
column
Exercise #2: Determining the Possible Make
of Firearm Based on Class Characteristics
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The results of using the
GRC chart will often
result in multiple
possibilities that fall
within that bracket of
measurements
Exercise #3: Cartridge Case Characteristics
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The headstamp markings
are located on the base
of the cartridge
The caliber is a numerical
designation typically
stamped on the base
You will need to note the
markings present on the
cartridge cases you
examine.
Exercise #3: Cartridge Case Characteristics
The breechface marks are
made from the cartridge
case coming in contact
with the breechface of the
slide of the firearm.
The marks can come in a
variety of patterns
including: parallel, circular,
smooth, and arched.
The breechface marks
present on the cartridge
cases will need to be
documented.
Exercise #3: Cartridge Case Characteristics
Firing pins are made in a
variety of shapes and sizes and
leave different types of marks.
You will be asked to sketch the
markings you observe in the
firing pin of the cartridge cases.
Exercise #3: Cartridge Case Characteristics
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The primer finish will
generally be either
nickel or brass.
The finish will need to
be noted on the
worksheet.
Exercise #3: Cartridge Case Characteristics
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Cartridge cases are
typically made from brass,
nickel plated brass, or
aluminum.
Nickel plated brass is shiny
and silver in color.
Aluminum cases are lighter
in weight than brass cases
and have a dull silver color
The cartridge case finish
will need to be
documented
Aluminum
Brass
Nickel
Plated
Exercise #3: Cartridge Case Characteristics
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Additional notes and
diagrams can include
any information
observed on the
cartridge including:
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Extractor Marks
Ejector Marks
Chamber Marks