A gun is a particular weapon that propels projectiles. The projectile is generally fired through a hollow tube known as the gun's barrel. The barrel's diameter, or caliber, determines the size of projectile used, which is usually designated in fractions of an inch or in millimeters. Differing from the musket, most modern guns are rifled, with a series of grooves spiraling along the barrel; exceptions include smoothbores on tanks, AFVs and some artillery.
"...una magna balista de cornu quae Domina Gunilda ...In non-military use it is often used synonymous with a "firearm", such as a personal handgun or pistol, or a hunting weapon.
The use of the term cannon is interchangeable with the gun as a word borrowed from the French language during the early 15th century, from Old French canon, itself a borrowing from the Italian cannone, a "large tube" augmentive of Latin canna "reed or cane".
In military use, the term "gun" refers to artillery ordnance that fires projectiles at high velocity, such as naval guns which in the modern navies are not called cannons, or the tank main gun. In military use, mortars and all hand-held firearms are excluded from the definition of guns because they do not require the accurate gunnery data calculations and training when engaging targets. Two exceptions to this include: the shotgun, which is a smoothbore hand-held firearm that fires a load of shot or a single projectile known as a slug, and the machine gun, which is a fully-automatic weapon mounted on a tripod or wheeled carriage and is almost always operated by a crew of two.
In a gun-type fission weapon the "gun" is part of a nuclear weapon. The projectile is fissile material that is fired and captured inside the device. In the case of nuclear artillery, it should not be confused with the gun that fires the whole warhead. In a captive bolt gun the projectile is also caught within the mechanism. Such captive piston guns are often used to humanely stun farm animals for slaughter.
A gunner is a member of the team charged with the task of operating and firing a gun.