Ammunition is basically any explosive device, from the tiny cartridge in a starting pistol to a massive ten-ton bomb.
The word ammunition is derived from the Latin munire, meaning "to fortify," and originally meant fortifications and the tools of war. The modern definition states that ammunition is any military device that includes components filled with explosive, smoke-producing, incendiary (fire producing), or pyrotechnic (illuminating) compositions. However, this definition would exclude many other items, for example, shotgun cartridges, distress and signaling rockets, engineering explosives, chemicals weapons, aircraft ejection seat cartridges, and even fireworks, all of which can be considered as types of ammunition.
Explosives
All ammunition contains explosive material in one form or another, and the way they function and release their energy may be precisely controlled.
Explosives are substances that can be converted into hot gases or volatile products and in the process exert a sudden pressure on the surroundings. The speed of the reaction determines the precise application of the explosive substance. High explosives react fast, usually within a few millionths of a second, and produce a sudden and disruptive increase in pressure that causes a severe shock wave. The tremendous power released by this detonation can be used to burst a shell into small, lethal fragments. Low explosives are slower, taking a few thousandths of a second to react. The pressure produced can be used in a gun, for example, to propel a shell. Typical high explosives as used in shells, bombs, land and sea mines, grenades, and demolition work are trinitrotoluene (TNT), gelignite, hexogen, tetryl, and pentaerythritol tetranitrate (PETN). Nitrocellulose is a typical low explosive used in most modern guns as a propellant.
Gun ammunition
Ammunition for guns, whatever the size, comprises a propellant charge and a projectile. The two items may be secured permanently together (fixed), supplied as individual items and put together before loading (semifixed), or kept and loaded separately (separate loading). The deciding factors are, first, the method of gas sealing, or obturation, adopted and, second, the gun’s barrel size, or caliber. The charge is sealed off in the gun’s chamber either by means of a pad fitted to the breach or by enclosing the propellant in a cartridge case. Gas pressure from the burning propellant expands the pad or the case to seal off the rear of the charge completely. The projectile fits snugly in the barrel, preventing a forward leak of gas. As the bore (internal diameter) of the gun increases, the charge and projectile become heavier and more cumbersome to handle, and it is necessary to load them separately.
Components
A round of ammunition comprises the propellant, or charge, and the projectile, or shell. For a typical fixed round, the cartridge case is usually made of brass, 70 parts copper to 30 of zinc. The brass is pressed into shape in a series of stages, which harden and strengthen the metal. By alternately working and annealing, at about 1112°F (600°C), the case can be made thick and hard at the base to take the initiating cap and primer and to withstand the forces of loading and extraction. The center section is made softer, so it can expand and seal against the chamber wall, and the nose is harder so it can be crimped firmly to the shell. Other materials, such as steel, aluminum, and plastics, as well as cheaper methods of construction, are also in use today. The development of a small arms round with such durable propellant explosive that no cartridge case is necessary has resulted in ammunition in which the entire charge section is consumed when the round is fired.
The propellant may be in the form of small grains, short or long cords, or a solid block perforated by slots of holes to control the speed of burning. It is ignited by the primer. This comprises a small quantity of a very sensitive explosive that is initiated, or detonated, either when the striker pinches it between the cup and anvil or by an electric impulse. The flash is passed to a few grains of gunpowder that ignites to set off the propellant-the main charge.
The shell, or projectile, has three main components: the high-explosive filling, the driving band, and the fuse. Shells are normally forged from a good quality steel, and the final shape is the result of three or more operations and some machining to achieve the required tolerances. The projectile’s shape is determined by a number of factors. For a stable flight, it should be no longer than five times the caliber. For low skin friction (the friction acting on the surface of a body moving through air), it should be smooth and the base should be streamlined to reduce aerodynamic drag. The driving band is a copper ring forced into a groove cut around the lower section of the body. Its tasks are to provide a good gas seal in front of the charge, to seat the projectile in the bore, and to engage the spiral rifling of the gun barrel to make the shell spin. The shell body is filled with high explosive, for example, TNT, by pouring molten explosive into the cavity, taking care to ensure no empty spaces are formed on cooling. A ratio of 15 percent explosive to the total shell weight is normal.
The explosive in the projectile is itself the propellant of the warhead. At the simplest level, it splinters its casing into lethal fragments of shrapnel, but even then, the case may be notched in sections to create a specific shape of shrapnel. When a shell is used against armored fighting vehicles, the explosive may be distributed through the warhead in a way that is designed to direct all its force into a narrow channel capable of piercing armor plate. There are also cluster munitions, which carry a mass of submunitions to be released over the target.
