Byron,
try Mink Oil, its available from Track of the Wolf, and its pretty cheap. I am using it during the Winter here in Western Australia, now we don't get snow like you blokes do, but gets cold all the same, and you can leave the rifle loaded for a few weeks if necessary, my little .36 Leman is ready for any crow that annoy our chooks !!
Cheers
Heelerau.
Ps when looking for a load, only change one thing at a time and fire say 5 shot groups off a solid rest. I would be surprised if a patched ball rifle would ever lead, as the ball is patched. Roughness of the bore is a definite no no, uneven seating pressure of the ball will spread shots as well.