ORIGINAL: cayugad
Do yourself a favor.. throw the bore butter away. Use a quality gun oil like Rem Oil, Break Free CLP, Birchwood Casey Barricade (my favorite), and swab the bore with that. That will protect the rifle from rusting.
2nd that advice...I've been using Knight's "Knight Oil" with rust inhibitor for a few years now and it works great...no rust on any of the muzzleloaders I've shot.