A gun is a weapon that uses rapidly expanding gases to accelerate a projectile—a bullet or shell—through a cylindrical barrel. Guns range in size from small handguns for close-range attack to enormous artillery guns that can fire projectiles over ranges of around 15 to 100 miles (around 25–160 km). Most guns use explosive charges to provide the expanding gases that impart energy to projectiles; some small weapons use the release of compressed air to the same effect.
Basic principles
The effectiveness of a gun is measured in terms of its ability to deliver an appropriate projectile to its target with sufficient kinetic energy to cause the required extent of damage. How this is achieved varies according to the intended range of fire.
For short-range weapons, the trajectories of projectiles are short enough for the effects of gravity to be minimal, and the projectile follows an essentially straight path along the line of the sights. An acceptable accuracy of fire is achieved through careful barrel design and high-precision manufacture. The design and choice of construction materials are intended to limit the extent of barrel distortion and uneven wear caused by repeated firing. These measures help ensure that a weapon maintains a high degree of accuracy of aim throughout its projected working life.
Some guns have rifling—helical grooves in the inner surfaces of their barrels—that cause a projectile to spin around an axis that coincides with its line of flight. The gyroscopic effect of this spin contributes to stable flight and better accuracy.
Projectiles from long-range guns follow arch-shaped trajectories. The direction and speed of the projectile as it leaves the barrel and acceleration owing to gravity are the main factors that determine the flight path. Air resistance presents a force that retards the motion of the projectile, and atmospheric conditions, such as wind and rain, also have an influence on trajectory.
The greater the range of a gun, the more accurate must be the aim if the projectile is to stand a reasonable chance of hitting its target. Modern long-range guns use laser range finders and computerized aiming systems to ensure a high accuracy of fire; some of these systems take into account changes in barrel characteristics caused by wear and adjust the aim accordingly.
Early guns
Around 1250 B.C.E., the Chinese developed the first weapons to launch projectiles using exploding gunpowder rather than a mechanical device, such as a bow or catapult. Instead of the bullets or balls used with later firearms, these devices launched arrows at their targets.
Historical reports indicate that forerunners of most types of modern guns developed in Europe during the early 14th century. Cannon that used gunpowder to launch stones and metal balls were reported in 1326, and there is some evidence for even earlier use of firearms.
Early guns and cannon were loaded through the muzzle with gunpowder, then a wad of paper, and then the projectile. Such weapons would be fired by igniting the gunpowder through a firelock—a narrow channel, filled with gunpowder, in the breech of the gun (the breech is at the opposite end of the barrel to the muzzle). The gunpowder in the firelock would be ignited by a hot wire or a slow-burning fuse of cord impregnated with potassium nitrate (KNO3), which promoted combustion of the cord material.
