A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the bullet, imparting spin around an axis corresponding to the orientation of the weapon. When the bullet leaves the barrel, the spin averages out curve from imperfections improving accuracy and prevents tumbling which improves range, in the same way that a properly thrown American football or rugby ball behaves. The word "rifle" originally referred to the grooving, and a rifle was called a "rifled gun." Rifles are used in warfare, hunting and shooting sports.
Typically, a bullet is propelled by the contained deflagration of an explosive compound (originally black powder, later cordite, and now nitrocellulose), although other means such as compressed air are used in air rifles, which are popular for vermin control, hunting small game, formal target shooting and casual shooting ("plinking").
Formerly, rifles only fired a single bullet with each squeeze of the trigger. Modern assault rifles are capable of firing more than one round per trigger squeeze; some fire in a fully automatic mode and others are limited to bursts of three to five rounds per squeeze. Thus, modern assault rifles overlap somewhat with machine guns. Generally, the difference between an automatic rifle and a machine gun comes down to weight and feed system; rifles, with their relatively light components (which overheat quickly) and small magazines, are incapable of sustained automatic fire in the way that machine guns are. While machine guns may require more than one operator, the rifle is an individual weapon.
