This is an interesting topic and it leads me to a further question, though it is a bit off-topic..
What was the prevalence of ex-military and unused surplus arms? Or put another way, was there a civilian market for them?
(I’m referring to the mil surp market, not weapons individually scavenged from a battlefield).
I seems to me that a well made, strong ex-government musket, purchased at a discounted price would be an attractive option for people of modest means, regardless of the .69-.75 bore size.
Yes, there was a civilian market for them. Sometimes the government issued or sold them to settlers and contractors as a cheap means of protection.
Some rifled muskets were bored out to smoothbore for using shot while foraging.
Sears and Roebuck listed for sale Civil War rifled muskets as-issued, and cut-down smooth bored versions for use as shotguns in the 1890’s.
A lot of people needed a relatively inexpensive gun to keep around the house or farm for protection and occasional use for hunting or getting rid of predators and other nuisance animals. Sometimes these guns would not be used for years at a time.
My great grandfather had a Civil War musket that had been bored out to about 20 gauge or a little smaller that he used in the 1890-1910 time frame, I think. When I was a teenager I remember asking him how well it worked as a shotgun. He said it worked just fine for squirrels and rabbits, hawks, skunks, coons, and all sorts of things that he sometimes had to shoot around the farm. Said one day he got several rats with one shot that were lined up side by side outside his barn drinking water that was dripping down from the eave of the roof during a rain that came at the end of a very bad drought one summer. The water had formed a little stream parallel to the wall on the ground and a dozen or so of the rats were lined up close together and focused on drinking the water. Got almost all of them with one shot.
I also asked him if he ever knew anyone else that had a bored out musket like his, and he said yes, several of the other farmers and other neighbors around there had them at one time or another, and liked them because buying the powder, caps, and shot was cheaper to buy than the shotgun shells for the cartridge guns, Most families had both muzzleloaders and breechloaders.
This was in the SW Missouri Ozarks region, where I live.