I remember a series of magazine articles many years ago on the guns of the (American) pioneers. The writer pointed out that most of the ML shotguns had the muzzles cut at a very slight angle from center to outward edge. It was surmised this was to facilitate something akin to "regulating" the guns for use with balls. Many of these people moving west with only those belongings fitting in a wagon (or less!) didn't have room for various guns even if they were affordable or available. Hence they choose a double shotgun offering two shots without reloading and could use shot or ball.

The number of different guns shown with documented history to the trek west seemed to endorse this idea. I sure wish I had those magazines today for reference but if this was true it's sure the idea had been around long before then.