Doubt very much that this was ever a pinfire .Question I ask is about the stock .Looks far to good for a gun of its age , so it has IMO either been very carefully renovated and re checkers or re- stocked in recent years .
Holes in the bottom ribs and tail piece/short rib suggest rust and possibly a re-soldered loop and that the barrels have been re- browned .Possibly a little leakage in doing so have had these drain holes drilled . Not uncommon .