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A bullet is a component of firearm ammunition and is the projectile expelled from the firearm’s barrel. The term is from Middle French and originated as the diminutive of the word boulle (boullet), which means “small ball”. Bullets are made of a variety of materials such as copper, lead, steel, polymer, rubber and even wax. They are available either singly as in muzzleloading and cap and ball firearms, or as a component of paper cartridges and much more commonly metallic cartridges. Bullets are made in a large number of shapes and constructions depending on the intended applications, including specialized functions such as hunting, target shooting, training and combat.
Though the word “bullet” is often used incorrectly in colloquial language to refer to a round of ammunition, a bullet is not a round of ammo but rather a component of one. A round of ammunition is a combination package of the bullet, cartridge, propellant and primer. This use of the term “bullet” when round is intended often leads to confusion when the components of a cartridge are intended.
Bullet sizes are expressed by their weights and diameters (referred to as “calibers”) in both imperial and metric measurement systems. For example: 55 grain .223 caliber bullets are of the same weight and caliber as 3.56 gram 5.56mm caliber bullets.
The bullets used in many cartridges are fired at muzzle velocities faster than the speed of sound — about 343 metres per second (1,130 ft/s) in dry air at 20 °C (68 °F) — and thus can travel a substantial distance to a target before a nearby observer hears the sound of the shot. The sound of gunfire (i.e. the muzzle report) is often accompanied with a loud bullwhip-like crack as the supersonic bullet pierces through the air creating a sonic boom. Bullet speeds at various stages of flight depend on intrinsic factors such as its sectional density, aerodynamic profile and ballistic coefficient, and extrinsic factors such as barometric pressure, humidity, air temperature and wind speed. Subsonic cartridges fire bullets slower than the speed of sound so there is no sonic boom. This means that a subsonic cartridge, such as .45 ACP, can be substantially quieter than a supersonic cartridge such as the .223 Remington, even without the use of a suppressor.
Bullets do not normally contain explosives, but damage the intended target by transferring kinetic energy upon impact and penetration (see terminal ballistics).
The first use of gunpowder in Europe was recorded in 1247. It had been used in China for hundreds of years. The cannon appeared in 1327. Later in 1364, the hand cannon appeared. Early projectiles were made of stone. Stone was used in cannon and hand cannon. In cannon it was eventually found that stone would not penetrate stone fortifications which gave rise to the use of heavier metals for the round projectiles. Hand cannon projectiles developed in a similar fashion following the failure of stone from siege cannon. The first recorded instance of a metal ball from a hand cannon penetrating armor occurred in 1425. In this photograph of shot retrieved from the wreck of the Mary Rose which was sunk in 1545 and raised in 1982. The round shot are clearly of different sizes and some are stone while others are cast iron.
Matchlock musket balls, alleged to have been discovered at Naseby battlefield
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 round musket ball was smaller than the bore of the barrel. It was loaded into the barrel wrapped in a loose fitting cotton patch that held the bullet firmly in the barrel and against the powder. (Bullets not firmly on the powder risked exploding the barrel, with the condition known as a “short start”.