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.

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.