Chapter 8

Firearms Characteristics
All barrel irrespective of the type of the weapons for which they are made, are

manufactured from a solid piece of metal. The metal from which the barrel is made is

carefully selected for its chemical and metallurgical properties, thus assuring a high-

quality product after the various machine operations and heat treatment are completed.

Stages in the manufacture of barrel

A. Drilling

A special deep-hole is used through the center of which lubricating oil is forced

under pressure. This operation results to a comparatively rough hole of uniform

diameter from one end of the barrel to other. At this stage the interior surface of the

barrel will bears numerous sears and scratches resulting from the irregular cutting of

the drill and the metal chips, which mark the finish.

B. Reaming

In this process some of the scars or scratches left by the drilling operation are

remove. The reamer removes metal from the entire surface because it is slightly

larger in diameter than the drill, which completes the bore operations. It includes

roughly, finishing and burnishing reamer to have a smooth bore barrel.

C. Rifling

This process necessary for the making of the helical groves inside the barrel and

such can be performed in any of the following methods:

1. Hook – cutter system (cutter)

2. Scrape – cutter system (scraper)

3. Broaching system – (broach)

4. Button – system (button)

D. Lapped

This is the polishing operation in which a lead plug closely fitting the inside of

the barrel is drawn back and forth on a rod carrying with is a polishing compound.

This will remove large imperfection on the side surface of the barrel both to the lands

and the grooves. What is important about this process is that no matter how many

times we polish or finish large imperfections maybe eliminated but not the minute
imperfections making a series of striations that will be impressed on every bullet that

will pass through it. This is the basis for which firearms is identified.

The Breech face

Just like any barrel of every firearm, the breech face also bears with it the same

important. It is that portion of the firearms against which the shell or the cartridge case

and the primer is pressed backward every time that a cartridge is fired in the chamber. If

these things happen the base of the cartridge will be marked by the gun.

This is due to the fact that every breech face of a firearm just like the barrel are

made up of a harder metal than any cartridge case or bullet, thus, the principle that

when a softer surface comes in contact with a harder on it is always the softer surface

that characteristic that harder surface has.

Types of Characteristics in Firearms

A. Class Characteristics = are those properties or attributes of a firearms which

can be determined even before the manufacture of the gun. This is true for such

characteristics are considered to be a manufacture’s designs or specifications and

security.

Class Characteristics of Firearms

1. Bore diameter (caliber or gauge) it is diameter to which the bore was

reamed. The distance measured between two opposite lands inside the bore in a

hundredths or thousandths of an inch. In most express in either caliber in inch or

in millimeters such Cal. .22, .25, .30, .32, . 38, .380, .357, .44, .45, .50, etc. or

5.56mm, 6.35mm, 9mm, 11mm, etc. in shotgun they are either in gauge or in

inch , such as in 10 gauge (), 12 gauge (.729), 20 gauge (.615), 24 gauge (579),

30 gauge (.537)36 gauge (.615), 30 gauge (.729), 20 gauge (.615), 24 gauge

(.579),30 gauge (.537) 36 gauge (.506) and the smallest which is .410.

2. Number of lands and grooves = the number of lands an grooves inside

the barrel of a given firearm are always the same or equal. It may run from 3 to 8,

but the most in the modern firearm are five and six.

Lands = are the elevated portion of the bore of the firearm.

Grooves = are the depressed portion of the bore between the lands.
3. Width of the lands = is dependent upon the bore diameter of the gun,

grooves, width and number. The lands are the remainders of the circumference

after subtracting all the grooves width.

4. Width of the Grooves = is measured as the shortest distance between the

two dies or edge of a grooves.

5. Direction of Twist = rifling inside the barrel of the gun is either twisted to

the left or to the right which cause bullet to rotate as it passes through the bore,

in order to ensure gyroscopic stability in its flight.

6. Pitch of Rifling = it is the measure of the twisting of the lands and

grooves. It refers to the measure of the distance advance by the rifling in order to

make a complete turn inside the barrel.

7. Depth of the Grooves = the groove’s depth if measured on a radius of the

bore. Grooves are usually few thousandths of an inch deep, which equal to the

height of the lands.

B. Individual Characteristics = are meant for those characteristics which are

being determined only after the firearm was already been manufactured. They are

the product of machine imperfections and some later due to the used of the firearms.

Types of Rifling

1. Steyer Type= is the type of rifling having four (4) lands and grooves, right

twist and the width of the lands grooves. (4 RG=L)

2. Carbine Type = rifling having (4) lands and grooves, right twist, the width

of the grooves is two (2) times the width of the lands (4RG2X).

3. Smith and Wesson = rifling having (5) lands and grooves, right hand

twist , the width of the land and grooves are equal. (5RG=L)

4. Colt = type of rifling having six (6) lands and grooves, left twist, the width of

the grooves is twice (2) the width of the lands. (6LG2X)

5. Browning = type of rifling having (6) lands and grooves, right hand twist,

the width of the grooves is twice the width of the lands. (6RG2X)

6. Webley = Rifling having seven (7) lands and grooves, right hand twist, the

width of the groove is three time larger than the boarder of the lands. (7RG3X)
7. Winchester = Rifling having six (6) lands and grooves, right hand twist, the

width of the grooves is three time larger the width of the lands.

Individual Characteristics in Firearms

Individual Characteristics in firearms are usually determined by the test

firing which will give us both the test bullet and the test shell that will show the

individuality of its property based on the left marks on every bullet and shell fired

from it. Such marks are so minute that the use of the lens with high magnification

is necessary to discover individuality.

Marks left on fired shells or fired bullets are generally categorized as

to either accidental or repetitive. Accidental marks are those marks that may bare

some importance to the investigation but are considered of not much value in the

identification of the particular firearm or weapon since they are not regularly

formed in the operation of the gun. On the other hand, Repetitive marks are

those marks, which are very useful in identifying a firearm. They show identity of

performance.

Marks found of Fired Bullets

1. Land Marks = marks left on a

Land Mark
fired bullet caused by its contact to the

elevated portion (lands) of the bore of

the firearm. It appears as slight

depressions or scratches the

Groove
cylindrical surface of the fired bullet. Mark

This considered as one of the most important mark found on a fired bullet used

for the purposes of identification.

2. Groove Marks = marks found on a fired bullet caused by the grooves of

the barrel which is the same number as that of the landmarks.

3. Skid Marks = Marks that are generally found on fired bullet from a

revolver. It is more or less located at the anterior portion of the fired bullet due to

its forward movement from the chamber to the barrel of the gun before it initially

rotates.
4. Stripping Marks = marks found on those bullet fired from a “loose-fit”

barrel wherein the rifling are already been badly worn-out.

Worn-out in the rifling of the firearms can be cause by either chemical

reaction brought about by rust (corrosion) or through excessive use (erosion)

5. Shaving Marks = marks commonly found on bullet fired from a revolver

cause by its forward movement to the barrel that is poorly aligned to the cylinder.

6. Slippage Marks = marks found on fired bullets passing through either on

oily or oversize barrel.

Marks found on Fired Shells

1. Firing Pin Mark = mark generally

found at the base portion of the cartridge

case more specifically near center of the

primer cup in a center fire cartridge or at the

rim cavity of a rim-fire cartridge.

Considered as one of the most important

marks for identification of firearms using fired

shell.

2. Breech Face Mark = mark found at

the base portion of the shell cause by backward movement to the breech face of

the block of the firearm. This is also one of the important marks in shell

identification.

3. Extractor Mark = mark mostly found at the extracting groove of the fired

cartridge case. Cause by its withdrawal from the chamber.

4. Ejector mark = mark generally found on cartridge case fired from an

automatic firearms. It is located near the rim of the case cause by the throwing of

shell from the firearm to the area of shooting.

5. Shearing Mark = sometimes called “Secondary Firing Pin mark” found in

the primer near the firing pin mark.

6. Magazine Lip Mark = marking found at the two sides of the rim cause by

the magazine lips during the loading of the cartridge into the magazine for firing.
7. Chamber Mark = mark mostly found around the body of the fired cartridge

case cause bi the irregularities of nips inside the walls of the chamber.

In fired cartridge case either of the Firing pin mark and the Breech face

marks can be used as basis for identification, in the absence or none use of

these two, both the ejector and extractor marks can be utilized as secondary

choice.