The term gun model includes the barrel through which the projectile passes and the breach which closes the barrel ready for the propellant to ignite.
I have used the term gun model rather than "gun" as gun should strictly refer to an individual gun (perhaps serial number 223) that was built to the design of the gun model.
A gun model needs to be mounted in a turret model before it is useable. The turret model allows the barrel (or barrels) to elevate (up and down) and to train (side to side). The turret model may provide other services and facilities necessary for the operation of the gun.
