Swivel gun

The term swivel gun usually refers to a small cannon, mounted on a swiveling stand or fork which allows a very wide arc of movement. Another type of firearm referred to as a swivel gun was an early flintlock combination gun with two barrels that rotated along their axes to allow the shooter to switch between rifled and smoothbore barrels.

They were wielded by Murtogg & Mullroy while they were tasked with guarding the Dead Man's Chest, training the cannons on it to prevent Davy Jones from regaining control of his ship.