I think I have found the most likely contender.
Apparently the American Govt. converted a huge amount of Civil War .58cal Springfield's to trapdoor models.
They then found out that they were too large a bore and refitted .50-70 barrels and subsequently the .45-70 Carbine was born.
This is the same weapon issued to Custers troops at The Little Bighorn.
As you can imagine, a lot of these must have found their way into civilian hands.
So hopefully, mystery solved,
regards, Angel Eyes..............YEEEEEEEHAAAAAAA!!!
Forty Rod, you been hanging out in Ladies underwear again