i have a .54 flint lock CVA which i purchased used off of either historical trekker or frontierfolks forum.
this rifle was a kit someone had slammed together and needing a lot of reshaping & finishing.
it turned out very nice with about 30-40 hrs of work.
i have shot it with patched balls with no misgivings whatsoever on safety.
wish i could post a picture..i don't know how to and this rifle is the nicest one i've ever done....
if you are going for historical /period correctness. check out some sites of the customer makers then decide if you want full stock or half stock. yes, there was full stock hawken rifles.....
most any of the italian guns in a kit can be spruced up. the lymen plains rifle has a very good reputation & i believe it can be purchased in percussion or flint 50-54 caliber.
check the track of the wolf. you will have many rifles flint/percussion custom made for sale as well as factory kits & custom kits from TOTW.