stun gun, hand-held electronic device that produces a high-voltage pulse that can immobilize a person for several minutes with no permanent damage in most cases. It is powered by ordinary batteries, which supply power to a circuit containing transformers, oscillators, capacitors, and electrodes. In some versions the electrodes are connected to the gun by wires and may be shot at a person. The transformers increase the voltage in the circuit to between 20,000 and 150,000 V and reduce the current proportionally. The oscillators fluctuate the current to produce a specific pulse frequency, and the current charges the capacitors. Connecting the electrodes to a person's body releases high-voltage electrical energy at a frequency pattern designed to interfere with the neurological impulses that travel through the human body to control voluntary muscle movement. The use of stun guns has been associated with death in some cases, typically when the person on whom the gun was used on has taken drugs or has a pre-existing heart condition. The degree to which the stun gun may have contributed to the deaths is unclear, but studies with pigs have shown that repeated shocks can cause heart stress.

machine gun: see small arms.

gun control, government limitation of the purchase and ownership of firearms. The availability of guns is controlled by nations and localities throughout the world. In the United States the "right of the people to keep and bear arms" is guaranteed by the Constitution, but has been variously interpreted through the years. Since the late 1930s federal judicial and law enforcement officials generally held that the right exists mainly in the context of the maintenance of a state militia, but in 2002 the Justice Dept., under Attorney General John Ashcroft, indicated that it interpreted the amendment as more broadly supporting the rights of individuals to possess and bear firearms. Such an interpretation was upheld by a 2008 Supreme Court decision that nonetheless did not challenge the government's right to place some limitations on the ownership and possession of firearms.

Some U.S. states and localities have enacted strict licensing and other control measures, and federal legislation (1968) prohibited the sale of rifles by mail. Gun control has continued to be widely debated, however, and has often been opposed, notably by the National Rifle Association (NRA). Increasing gun-related crimes together with citizen pressure propelled congressional passage (1993) of the "Brady bill" (named for James Brady, the press secretary seriously wounded in the 1981 assassination attempt on President Ronald Reagan) after years of controversy. It required a minimum of a five-day waiting period and background check before a handgun purchase. Parts of the bill were challenged in court and in 1997 the Supreme Court invalidated its background-check provision. The 1994 Crime Bill outlawed the manufacture, sale, and possession of military-style assault weapons, but it expired in 2004. In 1999, following a rash of shootings at U.S. schools, further gun-control legislation was passed by the Senate but was voted down by the House of Representatives. Attempts by localities (through legislation) and individuals (through lawsuits) to pursue gun control through the courts by permitting or bringing negligence suits against a gun manufacturer or dealer when a weapon it made or sold is used in a crime led many states and, in 2005, Congress to pass laws limiting such suits.

gun, in general, any weapon that discharges shot, shells, or bullets by the explosion of gunpowder or some other explosive from a straight tube. See firearm; artillery; small arms.

Lightweight automatic small-arms weapon chambered for relatively low-energy pistol cartridges and fired from the hip or shoulder. Submachine guns usually have box-type magazines that hold 10–50 cartridges, or occasionally drums holding more rounds. A short-range weapon, they are rarely effective at more than 200 yards (180 m). They can fire 650 or more rounds per minute and weigh 6–10 lbs (2.5–4.5 kg). Important types include the Thompson submachine gun, or tommy gun (patented 1920), the British Sten gun of World War II, and the later Israeli Uzi.

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Automatic weapon capable of rapid, sustained fire, usually 500–1,000 rounds per minute. Developed in the late 19th century by such inventors as Hiram Maxim, it profoundly altered modern warfare. The World War I battlefield was dominated by the belt-fed machine gun, which remained little changed into World War II. Modern machine guns are classified into three groups: the squad automatic weapon, chambered for small-calibre assault-rifle ammunition and operated by one soldier; the general-purpose machine gun, firing full-power rifle ammunition and operated by two; and the heavy machine gun, firing rounds of 12.7 mm (.5 in) or higher and often mounted on an armoured vehicle. Seealso submachine gun.

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Weapon consisting essentially of a metal tube from which a missile or projectile is shot by the force of exploding gunpowder or some other propellant. The term is often limited today to the so-called big guns, cannon larger than a howitzer or mortar. It may also be used to refer to military small arms such as the rifle, machine gun, and pistol, as well as to nonmilitary firearms such as the shotgun. Though the Chinese used gunpowder in warfare from the 9th century, guns were not developed until the Europeans acquired gunpowder in the 13th century. The earliest guns (circa 1327) resembled old-fashioned soda bottles; they apparently were fired by applying a red-hot wire to a touchhole drilled through the top. Separating the barrel and the powder chamber resulted in breechloaders, which continued to be used in naval swivel guns and fortress wallpieces well into the 17th century. Small arms, as distinguished from hand cannon, did not exist until the development of the matchlock in the 15th century. Seealso flintlock, wheel lock.

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Artillery piece fired from the ground or shipboard in defense against aerial attack. They were first used in combat in World War I, when field artillery were converted to antiaircraft use by mountings that enabled them to fire nearly vertically. Range finders and searchlights, developed in the 1920s and '30s, increased their effectiveness. Advances in World War II included rapid-firing and automatic weapons, radar for target tracking, and radio-operated fuses. British and U.S. forces used a 40-mm gun that fired ammunition to a height of 2 mi (3.2 km). Heavier guns, up to 120 mm, were used against high-flying bombers. For most of the war, the most effective was the German 88-mm Fliegerabwehrkanone; its abbreviated name, flak, became a universal term for antiaircraft fire. With the introduction of guided missiles in the 1950s and '60s, heavy antiaircraft guns were phased out, though lighter radar-guided automatic guns remained effective against low-flying aircraft and helicopters.

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