I can answer one part of this. Though in some places like the Appalachians muzzleloading black powder guns were not uncommon going into the 20th c. because they only needed black powder, lead, and percussion caps, most of the US went to cartridge guns after about 1874 , when the American target shooting team with cartridge rifles won against the English teams with muzzleloaders in a big competition at Bisley in the UK. Shooters in the US could and would reload centerfire black powder cartridges like 45-70 and 40-82 themselves, and did. The little "tong tools" for doing it sometimes still pop up for sale. After 1890 most armies went to smokeless ammunition, but when cartridge companies started making smokeless ammo for the civilian market, civilians at first couldn't buy smokeless powder, so they couldn't reload their own ammunition. Considering smokeless is more powerful, difficult to use, this may have been a good thing at first- probably saved some lives. But for those wanting to learn to use the new powder, this was something of a problem, and although some people around gunsmith Otto Niedner tried to see if they could actually make their own nitrocellulose, smokeless powder for reloading really wasn't available until around after 1907. There was at least one cartridge, 32 Winchester, that was actually designed so it could be sold loaded with smokeless and yet could be reloaded with black powder...but the result was very mediocre. So black powder cartridges continued to be made for quite some time ( 45-70 is still made- not black powder but reduced pressure loads) .