티스토리 뷰
Bullets for Beginners Background
The ultimate goal of all weapons systems is to destroy the target. one of the basic properties by which a weapon's effectiveness is measured is the quantity of energy, and thus damage potential, it delivers to the target. Modern weapons use both kinetic and potential energy systems to achieve maximum lethality. Kinetic energy systems rely on the conversion of kinetic energy (1/2 MV2) into work, while potential energy systems use explosive energy directly in the form of heat and blast or by accelerating the warhead case fragments to increase their kinetic energy and damage volume.
A chemical explosive is a compound or mixture which, upon the application of heat or shock, decomposes or rearranges with extreme rapidity, yielding much gas and heat. Explosives are classified as low or high explosives accord-ing to their rates of decomposition. Low explosives burn rapidly (or deflagrate). High explosives ordinarily deton-ate. There is no sharp line of demarcation between low and high explosives. The chemical decomposition of an explosive may take years, days, hours, or a fraction of a second. The slower forms of decomposition take place in storage and are of interest only from a stability standpoint. Of more in-terest are the two rapid forms of decomposition, burning and detonation. The term "detonation" is used to describe an explosive phenomenon of almost instantaneous decomposition. The properties of the explosive indicate the class into which it falls. In some cases explosives may be made to fall into either class by the conditions under which they are initiated. For convenience, low and high explosives may be differentiated in the following manner.
- Low Explosives are normally employed as propellants. They undergo autocombustion at rates that vary from a few centimeters per second to approximately 400 meters per second. Included in this group are smokeless powders and pyrotechnics such as flares and illumination devices.
- High Explosives are normally employed in warheads. They undergo detonation at rates of 1,000 to 8,500 meters per second. High explosives are conventionally subdivided into two classes and differentiated by sensitivity:
- Primary. These are extremely sensitive to shock, friction, and heat. They will burn rapidly or detonate if ignited.
- Secondary. These are relatively insensitive to shock, friction, and heat. They may burn when ignited in small, unconfined quantities; detonation occurs otherwise.
The basic function of any weapon is to deliver a destructive force on an enemy target. Targets of today include military bases, factories, bridges, ships, tanks, missile launching sites, artillery emplacements, fortifications, and troop concentrations. Since each type of target presents a different physical destruction problem, a variety of general and special-purpose warheads are required, within the bounds of cost and logistical availability, so that each target may be attacked with maximum effectiveness.
The gas that causes the pressure that propels the projectile is generated by the ignition of an explosive train. This explosive train is termed a propellant train and consists primarily of low explosives instead of high explosives and has a primer, an igniter or igniting charge, and a propelling charge. Ignition of a small quantity of sensitive explosive, the primer (lead azide), is initiated by a blow from the firing pin and is transmitted and intensified by the igniter so that the large, relatively insensitive propelling charge burns in the proper manner and launches the projectile.
Gunpowders or smokeless powders are the propellants in use today. This substance is produced by combining nitrocellulose (nitric acid and cotton) with ether and alcohol to produce a low explosive. Although called smokeless powders, they are neither smokeless nor in powder form, but in granule form. Smokeless powders may be considered to be classed as either single or multibase powders.
In single-base powders, nitrocellulose is the only explosive present. Other ingredients and additives are added to obtain suitable form, desired burning characteristics, and stability. The standard singlebase smokeless powder used by the Navy is a uniform colloid of ether-alcohol and purified nitrocellulose to which, for purposes of chemical stability, is added a small quantity of diphenylamine.
The multibase powders may be divided into double-base and triple-base powders, both of which contain nitroglycerin to facilitate the dissolving of the nitrocellulose and enhance its explosive qualities. The nitroglycerin also increases the sensitivity, the flame temperature, burning rate, and tendency to detonate. The higher flame temperature serves to decrease the smoke and residue, but increases flash and gun-tube erosion. Double-base propellants have limited use in artillery weapons in the United States due to excessive gun-tube erosion, but are the standard propellants in most other countries. Double-base propellants are used in the United States for mortar propellants, small rocket engines, shotgun shells, the 7.62-mm NATO rifle cartridge, recoilless rifles, and the Navy's 5"/54-caliber gun.
Triple-base propellants are double-base propellants with the addition of nitroguandine to lower the flame temperature, which produces less tube erosion and flash. The major drawback is the limited supply of the raw material nitroguandine. At present, triple-base propellants are used in tank rounds and are being tested for new long-range artillery rounds.
Case guns which fire fixed ammunition employ propellant encased in a metal shell to which the projectile is attached, while bag guns employ propellant charges packed in silk bags. The use of bags is confined to large guns where the total propellant powder required to attain the required initial projectiles velocity is too great in weight and volume to be placed in a single rigid container. By packing the powder grains in bags, it is possible to divide the total charge into units that can be handled expeditiously by one man.