I never used Bore Butter for rust protection or storage. I'm on the BC Barricade bandwagon. I use enough to spray it right out of the nipples, then store muzzle-down to drain-out the flash channel on my percussion guns.
As Roundball mentioned, it (Bore Butter) can work--it's just a lot harder to deal with, creates a huge mess in order to make sure that every surface is coated, if you "check it" there's a chance you could wipe some off of a portion of what you're trying to protect, and using it requires extensive clean-up to get it all out.
In general, most ignition problems in percussion guns involve excess crud or moisture in the flash channel. Not removing all of the Bore Butter helps to create such a condition, and WILL lead to misfires! This is why I stick with Barricade and muzzle-down storage. A simple dry patch to wipe-out excess oil, then a couple caps & load it up and fire the gun all day long! What could be easier than THAT? If it ain't broke....
Dave
Black Powder Competitive Shooter, Hunter, Mentor
NRA CRSO
NMLRA Field Rep