Interesting reference to V.M. Starr lining vintage shotguns to .45-70
https://www.thehighroad.org/index.php?threads/homemade-double-barreled-muzzle-loader.701924/
"The barrels were cut to 25 inches and he regulated them to 80 yards with 300 grain HP bullets. His method was fairly direct. At the muzzle, he drove in wedges to move the liner. When they were hitting as he wanted them, he finished adding the solder and cut the wedges flush with the muzzle."

J.T. Phillips of Beede, Arkansas made flintlocks in the 80s-90s? Earlier? It would seem likely that the original Rubans Royal barrels were retired for the Crown barrels, but retained, and quite some time later converted to .45-70.

https://sites.google.com/a/damascusknowledge.com/www/home