Thanks for posting that Scott. The more I look at it, the more it definitely looks to have been stocked by someone not a professional stocker, but I might question the native theory. That I think would be difficult if not impossible to prove. Could be a piece put together out of necessity - frankly does look like it for certain - but the natives weren't the only folks 'needing' something that went bang.
I also would potentially speculate that it may be a much newer creation than might be initially considered, largely because the lock is still original flint while utilizing a barrel that was once on a revolving rifle dating after 1838. Also, making a breechplug and threading/breeching that barrel is no simple task, it would require quite a bit more than a "sorry knife." I kind of wonder if it might be a 'fun' piece put together by a hobbyist later, say late 19th century or early 20th century.
I really have no idea but those thoughts are circulating in my brain.
Sincerely, Curly.