GENERAL DISCUSSION
Definitions
a. Cartridge. A complete assembly
consisting of all the components necessary to fire
a weapon once; i.e., the cartridge case, primer,
propellant, and bullet or shot.
b. Cartridge Case. A container
designed to hold an ammunition primer and
propellant to which a bullet may be affixed. Its
profile and size conform to that of the chamber of
the weapon in which the cartridge is fired.
c. Primer. An assembly which
ignites the propellant.
d. Propellant. A low explosive
substance of fine granulation which, through
burning, pro-duces gases at a controlled rate to
provide the energy necessary to propel a bullet or
missile.
e. Bullet. A projectile fired, or
intended to 4 be fired from a small-arms
weapon.
f. Shot. A mass or load of
numerous, rela-tively small, lead pellets used in a
shotgun cartridge, as birdshot or buckshot.
Classification
a. Small-arms cartridges, based
upon type of case, are classified as centerfire or
rim-fire. In a centerfire cartridge, the primer is
located in a small well or pocket, in the center of
the cartridge case head. A rimfire cartridge
differs in that its priming mixture is loaded in
the flat rim at the base of the cartridge case.
This rim also serves to properly locate the
cartridge in the chamber and as a means of
extracting 'the cartridge case after firing.
The caliber .22 cartridge (other than hornet) is
the only current rimfire type used for military
purposes.
Centerfire cartridges may be
classified as rimless, semirimmed, or rimmed.
Depending upon its purpose,
small-arms cartridges for combat are classified
according to type as follows:
Armor-piercing
Armor-piercing-incendiary
Armor-piercing-incendiary-tracer
Ball
Ball, hornet
Grenade cartridges
Incendiary
Shotgun cartridge
Spotter-tracer
Tracer
In most types of small-arms
ammunition, a cartridge consists of a cartridge
case, primer, propellant, and bullet. A shotgun
cartridge differs in that it contains shot,
pellets, or a single slug. Construction of a
typical cartridge and its components is illustrated
above.
Cartridge Case
a. Classification. Small-arms
cartridge cases are either of the centerfire or
rimfire type. Centerfire cases are rimmed,
semi-rimmed, or aimless and have either solid or
folded heads. Semi-rimmed and rimless cases always
have solid heads, whereas rimmed cases used for low
pressure loading may have either solid or folded
heads.
From the standpoint of shape, cases
are known as straight, straight taper, or
bottleneck.
b. Functions. The cartridge case
has three functions. It is the means whereby the
other components; primer, propellant, and bullet
are assembled into a unit. It provides a waterproof
container for the propellant and primer. Another of
its functions is to expand and seal the chamber
against the escape of gases to the rear when the
cartridge is fired. This process of sealing by
expansion is termed obturation. An extractor groove
or rim, turned in the head of the cartridge case,
provides a means of removing the case from the
chamber of the weapon.
Shotgun cartridges and other
cartridges are manufactured with a rim at the
cartridge case head to facilitate extraction of the
fired case from the weapon.
c. Assembly. The primer is pressed
into the primer pocket of the cartridge case and
staked or crimped, and the joint is sealed by a
thin film of lacquer or varnish. The cartridge case
is then loaded with a charge of propellant powder,
and the inside of the neck coated with lacquer or
other waterproofing compound. The bullet is then
inserted, and the mouth of the case crimped into
the cannelure of the bullet.
For caliber 30 carbine and caliber
.45 cartridges, the mouth of the case is not
crimped to the bullet but is held in place by its
tight fit in the case. In some revolver cartridges
a cannelure in the case prevents the bullet from
L)eing seated too deeply.
d. Propellant Space. Propellant
space is the total inside volume of the case with
the bullet seated.
Propellant space is important in
the design of the cartridge because it determines
the maximum quantity of propellant that may be
used. The pressure of the expanding gases resulting
from the burning of the propellant is dependent
upon this volume. The manner in which the
propellant burns is influenced by any empty space
left in the case after the charge is loaded.
Shotgun cartridges differ as to propellant space,
depending upon specific kind or formula of
propellants used. The wad and construction of the
base of these cartridges are regulated in
manufacture so that there may be space left in the
case.
e. Headspace. (1) The term
"headspace" is defined as the linear
distance from the face of the fully closed bolt of
a weapon to one of several different reference
points, depending upon the gun chamber design.
(2) For rimless, bottleneck
cartridges, such as caliber .30, caliber .50, and
7.62 millimeter, headspace is the distance from the
shoulder of the chamber against which the shoulder
of the cartridge case rests to the face of the
closed bolt.
(3) For other rimless cartridges,
Such as caliber .30 carbine and caliber .45,
headspace is the distance from the shoulder of the
chamber against which the neck of the case tests to
the face of the closed bolt. It is thus very nearly
equal to the length of the cartridge case.
(4) For rimfire, rimmed, and
semi-rimmed centerfire cartridges, such as caliber
.22, caliber .38, and shotgun cartridges, the
extractor rim of the case stops the forward motion
of the cartridge. Therefore, headspace is equal to
the distance from the rear face of the chamber to
the face of the closed bolt. This is very nearly
equal to the thickness of the extractor rim.
Shotgun Cart?idge Cases. The
shotgun cartridge case consists of a brass or steel
head and a paper, case or shell body, or the case
may be made entirely of brass or aluminum. The head
is reinforced by a base of compressed paper in
which the primer pocket is formed. Some paper body
cartridges have a steel reinforcement called the
lining, under the metal head. The paper body
cartridge is water-proofed. The head is attached to
the cartridge body by crimping.
Primer
The primer assembly of centerfire
cartridges consists of a brass or gilding-metal cup
that contains a primer composition pellet of
sensitive explosive, a paper disk (foil), and a
brass anvil. A blow from the firing pin of a
small-arms weapon on the centers of the primer cup
compresses the primer composition violently between
the cup and the anvil, thus causing the composition
to explode. The holes or vents in the anvil allow
the flame to pass through the primer vent in the
cartridge case, thereby igniting the propellant.
The primer composition in the cup is held in place
and protected from moisture and electrolytic action
by a paper disk. The brass anvil is inserted last.
Primers of the noncorrosive type are now being used
in the manufacture of small-arms ammunition. In
order that primers may function properly, they must
be free from such surface defects as folds,
wrinkles, scratches, scales, or dents. Other primer
defects in cartridges are cocked, broken, or
inverted anvils; scratched, torn, or dirty cups;
and missing anvils, disks, or pellets. Rimfire
ammunition, such as the caliber .22 cartridge, does
not contain a primer assembly; the primer
composition is spun into the rim of the cartridge
case and the propellant is in intimate contact with
the composition. In firing, the firing pin strikes
the rim of the case and thus compresses the primer
composition and initiates its explosion.
Propellant
a. There are two types of
small-arms propellants generally used, the
single-base (nitrocellulose) type and the
double-base (nitrocellulose and nitroglycerine)
type. The weight of the propellant charge and
granulation of the propellant of a particular
composition are in accordance with specification
requirements. The weight of the propellant charge
is not constant: this weight is adjusted for each
propellant lot to give the required muzzle velocity
with the associated chamber pressure within the
limits prescribed for the weapon in which it is
fired. This charge is assembled loosely in the
cartridge case. Small-arms propellants are
manufactured in the form of small flakes, pellets,
sheets, spherical (ball) grains, or perforated
tubular grains. Acceptance requirements for
small-arms propellants are outlined in Military
Specifications MIL-P-3984. Since the propellant
grains of these charges are small, they are subject
to more rapid deterioration than larger grains
under abnormal temperature conditions. Small-arms
propellants is not as sensitive to friction as
black powder, but precautions used in handling
black powder should be observed in handing this
propellant.
b. Single-Base Propellant.
Single-base propellant is composed mainly of
nitrocellulose with a small quantity of tin and/or
potassium sulfate added to act as an antiflashing
agent. This composition is coated with
dinitrotoluene which acts as a moisture-proofing
agent, causes the first phase of the burning
process to take place at a relatively slower rate,
and has some antiflashing action. The coated
propellant is glazed with graphite to facilitate
the uniform action of automatic loading machines
and to avoid the development of large static
charges in blending and loading. Single-base
propellant is of a high order of extreme
temperature stability and is particularly resistant
to the effectsof atmospheric moisture. This
propellant is granulated as single perforated
grains.
c. Double-Base Proopellant.
Double-base propellant has two major ingredients,
nitrocellulose and nitroglycerin. These basic
ingredients are usually coated with dinitrotoluene,
dibutylphthalte, or centralite and glazed with
graphite in the same manner and for the same
purposes as in single-base propellant. This
Propellant is granulated as either spherical or
singie perforated grains. Double-base propellants
of early manufacture have approximately 40 percent
nitroglycerin content. This nitroglycerin content
has been reduced to 10 to 20 percent to make the
propellant more stable, cause less erosion of rifle
barrels, and have less tendency to flash.
d. Ball-Grain Propellant.
Double-base propellants are manufactured in the
form of spherical pellets or balls approximately
0.02 or 0.03 inch in diameter. These ball-grains
are rapidly replacing other forms of grains in
loading small-arms ammunition because of the
rapidity and economy of manufacture and the
flexibility of the process. Ball-grains are
produced by dissolving wet nitrocellulose in a
solvent, such as ethyl acetate, and adding
diphenylamine and chalk. Fof double-base
propellants, nitroglycerine would be added to the
above composition. By adding a protective colloid
and agitating the composition, the solution is
clispersed in the form of smill globules. When the
solvent is removed by heating, the propellant
solidifies in the form of spherical pellets or
balls. These balls of propellant are coated with
dinitrotoluene, centralite, or dipheiiylphthalate
to slow the initial phase of the burning process
and to act as a moisture proofing agent. The
propellant is then dried and coated with a glaze of
graphite.
e. Black Polvder. Black powder is
not used as a basic charge for small-arms
ammunition. Its only use in small-arins ammunition
at the present time is as an ingredient in
manufacturing Lesmok powder for use as a propellant
in caliber .22 cartridges, blank cartridges, and to
facilitate ignition in grenade cartridges.
f. Characteristics. Smokeless
powder for small-arms ammunition is usally glazed
with graphite to facilitate machine loading, and
thus presents a black polished appearance.
Single-perforated grains are usually used as
military small-arms propellants. For caliber .30
rifle ammunition, the diameter is approximately
0.03! inch. Since the propellant grains are smaii,
they ignite more rapidly and burn more quickly than
cannon propellant. When moisture is present or
abnormal temperatures prevail, small-arms
propellants are subject to more rapid deterioration
than larger grains. Smokeless powder is not as
sensitive to friction as black powder, but all
precautions used in handling black powder should be
observed for small grain propellants. A more
complete description of smokeless powders in
general will be found in TM 9-1900/TO 11A-1-20,
Ammunition General and TM 9-1910/TO 11A-1-34,
Military Explosives.
Bullet
a. General. Two types of bullets
are described here, the lead bullet and the metal
jacketed bullet. Lead bullets were originally
manufactured in the shape of a ball, but with the
advent of rifling in weapons, this ball was
replaced by a cylindrically shaped lead bullet
which would engage the rifling. Lead balls or shot
are still used in shotgun cartridges. Lead
cylindrical bullets of modern design are used in
caliber .22 ammunition and in many revolver
cartridges. Modern military cartridges and pistol
cartridges have bullets which consist of metal
jackets surrounding the lead alloy or steel
core.
b. Lead Alloy Bullets. The lead
used in this type bullet is combined with tin,
antimony, or both, for hardness. This alloying
reduces "leading" of the barrel of the
weapon, that is, the tendency of the lead to adhere
to the barrel in patches. It also helps to prevent
the bullet from "shipping," that is,
jumping the rifling of the weapon. Lead bullets are
generally lubricated with a grease or lubricating
compound which further prevents leading of the
barrel. Two or more cannelures, or grooves, around
the bullet contain the lubricant. Outside
lubricated bullets, like the caliber .22 and
caliber .38 short Colt, have cannelures and
lubricant on the outside when the bullet is
assembled in its cartridge case. The cannelures and
lubricant of inside lubricated bullets are beneath
the neck of the cartridge case and, hence, are not
visible in the assembled cartridge.
c. Jacketed Bullets. Jacketed
bullets have a lead or steel core covered by an
outside jacket of gilding metal or
gildiiig-metal-clad steel and are used to obtain
high velocities since lead bullets are not suited
for this purpose. Metal-jacketed bullets are used
in automatic pistols since lead bullets may be
damaged by the loading mechanism. A cannelure may
be cut or rolled in the jacket to provide a recess
into which the mouth of the case may be crimped at
assembly. The cannelure also serves to hold the
jacket and core together more firmly. An extra
cannelure may be added to identify the bullets
prior to assembly. d. Caliber. The caliber of a
weapon is the diameter of the bore of the weapon
measured from the surface of one land to the
surface of the land directly opposite. Caliber is
usually expressed in inches or in millimeters. When
expressed as a decimal without an indication of the
unit, the unit inches is understood. For example, a
caliber .30 cartridge has a bullet which is about
0.3085 inch in diameter. The lands of the rifling
of a weapon are the raised spiral portions of the
rifling formed by cutting spiral grooves, generally
0.003 or 0.004 inch deep, into the surface of the
bore. The diameter of a lead alloy bullet is
generally 0.003 inch greater than the bore diameter
between grooves. The diameter of a jacketed bullet
generally should not be more than 0.001 inch
greater than the diameter between grooves.
Types.
(1) Ball. Ball bullets are of the
lead alloy or the metal-jacketed type described in
b and c above respectively. The metal-jacketed ball
bullets have cores or slugs of various
compositions, depending on the intended use. Most
metal-jacketed ball bullets have a lead-antimony
slug. The caliber .50 ball bullet is a
metal-jacketed bullet containing a soft steel core
with a lead-antimony point filler to assure similar
ballistic properties for ball and armor-piercing
cartridges when used in functional packs. The 7.62
millimeter ball bullet of the cartridge, M59, is a
gilding-metal jacketed bullet containing a core of
plain carbon steel with a lead-antimony point and
base filler.
(2) Arnior-piereing. Armor-piercing
bullets are jacketed and have a core of hardened
steel which may be made of tungsten-chromium or
manganese-molybdenum steel. The 7.62-mm AP bullet
has both a point and base filler of lead-antimony.
The caliber .30 armor-piercing bullet has a point
filler of lead and a gilding-metal base filler
between the core and the jacket, whereas the
caliber .50 armor-piercing bullet has only a
lead-antimony point filler. These bullets have
smooth cannelures cut into the jacket for crimping
of the cartridge case.
(3) Armor-piercing-incendiary.
These bullets have a hardened steel core and a
point filler of incendiary mixture in-stead of
lead. (4) Armor-piercing-incendiary-tracer. These
bullets are similar to the
armor-piercing-incendiary bullets but in addition,
have a tracer composition in the base end.
(5) Incendiary. These bullets
contain core of incendiary mixture with a
lead-antimony slug at the base end. A hollow steel
cylindrical body or a clad steel container may be
inserted within the jacket and in front of the base
slug. The presence of two knurled cannelures is a
characteristic of caliber .50 incendiary
bullets.
(6) Tracer. These bullets contain a
lead-antimony slug in the forward position and a
tracer composition in the rear. They have either
square or boattailed bases. The bullet jackets are
made of gilding-metal or gilding-metal-clad steel.
An igniter composition is also present, which is
ignited by the burning propellant gases which, in
turn, ignites the tracer composition. Some tracer
bullets are visible the instant of firing while
others have a dim trace for a short distance from
the muzzle of the gun and then a bright trace
thereafter. Spotter-tracer bullets contain a tracer
element, and an incendiary charge which give off a
puff of smoke and a flash on impact with the
target.
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