Gun

A gun is a normally tubular weapon or other device designed to discharge projectiles or other material. The projectile may be solid, liquid, gas or energy and may be free, as with bullets and artillery shells, or captive as with Taser probes and whaling harpoons. The means of projection varies according to design but is usually effected by the action of gas pressure, either produced through the rapid combustion of a propellant or compressed and stored by mechanical means, operating on the projectile inside an open-ended tube in the fashion of a piston. The confined gas accelerates the movable projectile down the length of the tube imparting sufficient velocity to sustain the projectile's travel once the action of the gas ceases at the end of the tube or muzzle. Alternatively, acceleration via electromagnetic field generation may be employed in which case the tube may be dispensed with and a guide rail substituted.

Barrel
 Barrel types include rifled —a series of spiraled grooves or angles within the barrel—when the projectile requires an induced spin to stabilize it, and smoothbore when the projectile is stabilized by other means or rifling is undesired or unnecessary. Typically, interior barrel diameter and the associated projectile size is a means to identify gun variations.

Projectile
 A gun projectile may be a simple, single-piece item like a bullet, a casing containing a payload like a shotshell or explosive shell, or complex projectile like a sub-caliber projectile and sabot. The propellant may be air, an explosive solid, or an explosive liquid. Some variations like the Gyrojet and certain other types combine the projectile and propellant into a single item.

Terminology
 The term gun may refer to any sort of projectile weapon from large cannons to small sidearms including those that are usually hand-held. The word gun is also commonly used to describe objects which, while they are not themselves weapons, produce an effect or possess a form which is in some way evocative of a handgun or long gun.

The use of the term "cannon" is interchangeable with "gun" as words borrowed from the French language during the early 15th century CE, from Old French canon, itself a borrowing from the Italian cannone, a "large tube" augmentative of Latin canna "reed or cane".

 Autocannons are automatic guns designed primarily to fire shells and are mounted on a vehicle or other mount. [guns] are similar, but usually designed to fire simple projectiles. In some calibers and some usages, these two definitions overlap. o any large-caliber, direct-fire, high-velocity, flat-trajectory artillery piece employing an explosive-filled hollowed metal shell, solid or plasma bolt as its primary projectile. This later usage contrasts with large-caliber, high-angle, low-velocity, indirect-fire weapons such as howitzers, mortars , and grenade launchers which invariantly employ explosive-filled shells. In other military use, the term "gun " refers primarily to direct fire weapons that capitalize on their muzzle velocity for penetration or range. In modern parlance, these weapons are breech-loaded and built primarily for long range fire with a low or almost flat ballistic arc. A variation is the howitzer or gun-howitzer designed to offer the ability to fire both low or high-angle ballistic arcs. In this use, example guns include naval guns. A less strict application of the word is to identify one artillery weapon system or non-machine gun projectile armament on aircraft. Shotguns are normally civilian weapons used primarily for hunting. These weapons are typically smooth bored and fire a shell containing small lead slugs or steel balls. Variations use rifled barrels or fire other projectiles including solid lead slugs, a Taser projectile capable of stunning a target, or other payloads. In military versions, these weapons are often used to burst door hinges or locks in addition to antipersonnel uses.