A cannon is a large-caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder was the primary propellant before the invention of smokeless powder during the late 19th century. Cannons vary in gauge, effective range, mobility, rate of fire, angle of fire and firepower; different forms of cannon combine and balance these attributes in varying degrees, depending on their intended use on the battlefield. A cannon is a type of heavy artillery weapon.
Bronze cannon with inscription dated the 3rd year of the Zhiyuan era (1332) of the Yuan dynasty (1271–1368); it was discovered at the Yunju Temple of Fangshan District, Beijing in 1935.
A bronze "thousand ball thunder cannon" from the Huolongjing.
Earliest picture of a European cannon, "De Nobilitatibus Sapientii Et Prudentiis Regum", Walter de Milemete, 1326
Western European handgun, 1380
In guns, particularly firearms, but not artillery, where a different definition may apply, caliber is the specified nominal internal diameter of the gun barrel bore – regardless of how or where the bore is measured and whether the finished bore matches that specification. It is measured in inches or in millimeters. In the United States it is expressed in hundredths of an inch; in the United Kingdom in thousandths; and elsewhere in millimeters. For example, a US "45 caliber" firearm has a barrel diameter of roughly 0.45 inches (11.43mm). Barrel diameters can also be expressed using metric dimensions. For example, a "9 mm pistol" has a barrel diameter of about 9 millimeters. Since metric and US customary units do not convert evenly at this scale, metric conversions of caliber measured in decimal inches are typically approximations of the precise specifications in non-metric units, and vice versa.
Rifle cartridges: from left: 50 BMG • 300 Win Mag • 308 Winchester, 7.62 × 39 mm • 5.56 × 45 mm NATO • 22 LR
A 45 ACP hollowpoint (Federal HST) with two 22 LR cartridges for comparison
Side view of a Sellier & Bellot 45-cal ACP cartridge with a metric ruler for scale