.47 or .48 calibre rifles were somewhat common - back then. Since it is an original rifle with a somewhat less than perfect bore - I'd go with a slightly undersized ball if I could find a mould.
I would attempt to find a .475" to .480 mould. If you can get .480" from Track that would be the easiest direction to follow for balls.
I would also smooth up the crown a bit- with the end of my thumb & paper or emery - it looks almost usable as-is, just needs some smoothing, evening up.
I would use 8 to 10 ounce (not thousands of an inch) denim - or a heavy ticking running at least .020"., preferably a bit more.