The use of ML rifles hung on in a lot of places besides the Appalachians. There were quite a few still in use in rural areas in Southern Illinois. Gunmaker Henry Goedeke, in Olney, Illinois, didn't open his shop until 1873, and his rifles are not uncommon. When I started writing my book, there were two of Henry's sons still living, both in their 90's. They told me about watching their father rifle barrels and build rifles, up until around 1905.
Chunk gun matches went on in the Illinois/Indiana Wabash Valley for decades after 1900, and never completely died out.
I have a rifle made by G. Krug, Mt. Carmel, Illinois, that was carried into Northern Wisconsin by a family named Blamberg, who used the rifle to put venison on the table, up into the 1930's.