A rifle is a long-barrelled firearm designed for accurate shooting, with a barrel that has a helical pattern of grooves (rifling) cut into the bore wall. In keeping with their focus on accuracy, rifles are typically designed to be held with both hands and braced firmly against the shooter’s shoulder via a buttstock for stability during shooting. Rifles are used extensively in warfare, self defense, law enforcement, hunting, and shooting sports.
The term was originally rifled gun, with the verb rifle referring to the early modern machining process of creating groovings with cutting tools. By the 20th century, the weapon had become so common that the modern noun rifle is now often used for any long-shaped handheld ranged weapon designed for well-aimed discharge activated by a trigger (e.g., personnel halting and stimulation response rifle, which is actually a laser dazzler).
(A Henry rifle, the first successful lever action repeating rifle)
Like all typical firearms, a rifle’s projectile (bullet) is propelled by the contained deflagration of a combustible propellant compound (originally black powder, later cordite, and now nitrocellulose), although other propulsive means such as compressed air are used in air rifles, which are popular for vermin control, small game hunting, competitive target shooting and casual sport shooting (plinking).
The distinct feature that separates a rifle from the earlier smoothbore long guns (e.g., arquebuses, muskets) is the rifling within its gun barrel. The raised areas of a barrel’s rifling are called lands, which make contact with and exert torque on the projectile as it moves down the bore, imparting a spin around its longitudinal axis. When the projectile leaves the barrel, this spin persists and lends gyroscopic stability to the projectile due to conservation of angular momentum, preventing yawing and tumbling in flight. This allows the use of more elongated and aerodynamically-efficient bullets (as opposed to the spherical balls used in smoothbore muskets) and thus improves range and accuracy.
The usual form of rifling was helical grooves in a round bore.
Some early rifled firearms had barrels with a twisted polygonal bore. The Whitworth rifle was the first such type designed to spin the round for accuracy. Bullets for these guns were made to match the shape of the bore so the bullet would grip the rifle bore and take a spin that way. These were generally large caliber weapons, and the ammunition still did not fit tightly in the barrel. Many different shapes and degrees of spiraling were used in experimental designs. One widely produced example was the Metford rifling in the Pattern 1888 Lee–Metford service rifle. Although uncommon, polygonal rifling is still used in some weapons today, one example being the Glock line of pistols (which fire standard bullets). Many of the early designs were prone to dangerous backfiring, which could lead to destruction of the weapon and serious injury to the person firing it
As the bullet enters the barrel, it inserts itself into the rifling, a process that gradually wears down the barrel, and also causes the barrel to heat up more rapidly. Therefore, some machine guns are equipped with quick-change barrels that can be swapped every few thousand rounds, or in earlier designs, were water-cooled. Unlike older carbon steel barrels, which were limited to around 1,000 shots before the extreme heat caused accuracy to fade, modern stainless steel barrels for target rifles are much more resistant to wear, allowing many thousands of rounds to be fired before accuracy drops. (Many shotguns and small arms have chrome-lined barrels to reduce wear and enhance corrosion resistance. This is rare on rifles designed for extreme accuracy, as the plating process is difficult and liable to reduce the effect of the rifling.) Modern ammunition has a hardened lead core with a softer outer cladding or jacket, typically of an alloy of copper and nickel – cupro-nickel. Some ammunition is coated with molybdenum disulfide to further reduce internal friction – the so-called ‘moly-coated’ bullet