Most think the muzzle loading double shotgun, was first, but IMO, that is backwards! I believe it is more likely that the first doubles were smooth bore muskets, that were primarily intended for ball, than shot, though both were used. It is more likely the double muskets were loaded and carried with ball, than with shot, because you would have need of a second quick shot for large animals than you would with birds, or small game, and the ball would act as protection against enemies better than shot! One of the first double RIFLES was an American thing in the form of a swivel barreled flint lock RIFLE, used in the colonies for hunting, and protection frm Indians. Many of the shotguns of that time were single barrels.

I think the double rifle came along long before the repeaters, and by the time the Percussion cap took over from the flintlock, most double rifles were no longer seen much, because of the speed of loading, and the comparitively long range of the long rifles. War weapons were still smooth bore till around the civil war in the colonies, and the big single shots had gone to the cape of good hope settlers in Africa, and india. These were very large bore guns, for very large animals in Africa, and in the colonies, we didn't need any thing other than a rifle that would kill a moose, or bear, and that could usually be done at longer range, so the single barrels cought hold here in the states, while The Britts started to buils double rifle, for the INDIA, and AFRICA holdings, where very large dangerous aniimals, and spear yealding locals were a worry!