I know that some guns that were originally rifles were converted to ball-and-shot guns later in their careers by simply reaming out the remaining rifling. But I wonder what the proportion of new purpose-made smoothbores to rifles was for the early frontier gunmakers. Suspect that most folks who wanted a smoothbore just used a worn out or discarded military musket or "trade fusil." But wonder how many purpose-built ball-and-shot guns there were....
I suspect that if you had a close look at some of the guns hung on walls in museums around the country as "classic Pennsylvania rifles," you would find that some of them never were rifles. Frontiersmen were very practical people and if they could use something for several purposes, they did. And, as you say, a carefully bored smoothbore with a tightly fitting ball can be very "woods accurate." And shoot shot, too.
