A rifle is a long-barreled 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, law enforcement, hunting, shooting sports, and crime. 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). Like all typical firearms, a rifle's projectile (bullet) is propelled by the contained deflagration of a combustible propellant compound (originally black powder and now nitrocellulose and other smokeless powders), although other propulsive means are used, such as compressed air 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 barrel. The raised areas of a barrel's rifling are called lands; they make contact with and exert torque on the projectile as it moves down the bore, imparting a spin. When the projectile leaves the barrel, this spin persists and lends gyroscopic stability to the projectile due to conservation of angular momentum, increasing accuracy and hence effective range. Early long rifles were muzzle-loaders firing spherical balls; the introduction of breech-loading allowed the use of elongated and aerodynamically efficient bullets, which did not yaw or tumble significantly in flight due to the spin. Terminology Historically, rifles only fired a single projectile with each squeeze of the trigger. Modern rifles are commonly classified as single-shot, bolt-action, semi-automatic, or automatic. Single-shot, bolt-action, and semi-automatic rifles are limited by their designs to fire a single shot for each trigger pull. Only automatic rifles are capable of firing more than one round per trigger squeeze; however, some automatic rifles are limited to fixed bursts of two, three, or more rounds per squeeze. Modern automatic rifles overlap to some extent in design and function with machine guns.