 The earliest combination guns were called "swivel guns" (not to be confused with the more widely known small cannon), which used a set of barrels designed to rotate to allow either the rifled or smoothbore barrel to line up with a flintlock mechanism.Modern combination guns tend to resemble double-barreled shotguns and double rifles, and are almost universally break open designs.Combination guns generally have a selector that allows the user to choose which barrel will fire.