Fwiw, a 30 bore is about .52 caliber, so that particular "confusion" isn't likely.
(I've wondered more than a few times if Hawken ever made .30 caliber plains rifles.)
One of the curators at HAM told me in 1979 (We were on our "several times delayed" wedding trip.) that he believed that most southerners, who went to the Mountain West as "free trappers", probably took southern-style flintlock squirrel rifles, as that was what they HAD.
(Obviously "company men" carried whatever weapons that their employer issued or required.)
yours, satx