A bullet is a projectile propelled by a firearm, sling, slingshot, or air gun. Bullets do not normally contain explosives,〔(The Exploding Bullet ) Journal of Clinical Pathology〕 but damage the intended target by impact and penetration. The word "bullet" is sometimes colloquially used to refer to ammunition in general, or to a cartridge, which is a combination of the bullet, case/shell, powder, and primer. This use of 'bullet', when 'cartridge' is intended, leads to confusion when the components of a cartridge are discussed or intended.
Bullets fired from slings, slingshots, and many airguns (including BB guns) travel well below the speed of sound (about 343 m/s or 1126 ft/s in dry air at 20 °C or 68 °F). Low-power handguns have muzzle velocities generally less than the speed of sound (subsonic), while bullets fired from high-power handguns (such as a .44 Magnum) and from rifles have an initial speed faster than the speed of sound, meaning they are supersonic and thus can travel a substantial distance and even hit a target before a nearby observer hears the "bang" of the shot. Bullet speed through air depends on a number of factors such as barometric pressure, humidity, air temperature, and wind speed.
The history of bullets far predates the history of firearms. Originally, bullets were made out of stone or purpose-made clay balls used as sling ammunition, as weapons and for hunting.
Eventually as firearms were developed, these same items were placed in front of a propellant charge of gunpowder at the end of a closed tube. As firearms became more technologically advanced, from 1500 to 1800, bullets changed very little. They remained simple ''round'' (spherical) lead balls, called ''rounds'', differing only in their diameter.
The development of the hand culverin and matchlock arquebus brought about the use of cast lead balls as projectiles. "Bullet" is derived from the French word ''boulette'' which roughly means ''little ball''. The original musket bullet was a spherical lead ball smaller than the bore, wrapped in a loosely fitted paper patch which served to hold the bullet in the barrel firmly upon the powder. (Bullets that were not firmly upon the powder upon firing risked causing the barrel to explode, with the condition known as a ''short start''.) The loading of muskets was, therefore, easy with the old smooth-bore Brown Bess and similar military muskets. The original muzzle-loading rifle, on the other hand, with a more closely fitting ball to take the rifling grooves, was more difficult to load, particularly when the bore of the barrel was fouled from previous firings. For this reason, early rifles were not generally used for military purposes.
The first half of the nineteenth century saw a distinct change in the shape and function of the bullet. In 1826, Delvigne, a French infantry officer, invented a breech with abrupt shoulders on which a spherical bullet was rammed down until it caught the rifling grooves. Delvigne's method, however, deformed the bullet and was inaccurate.
Square bullets, invented by James Puckle and Kyle Tunis, were briefly used in one version of the Puckle gun. The use of these was soon discontinued due to irregular and unpredictable flight patterns.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』