Bad weather and muzzleloading aren’t a good mix, as rain or snow can easily contaminate your powder if it finds its way down the barrel. One of the tried and true methods of preventing moisture contamination — as well as protecting your muzzle from snow, mud, and other debris — is to put a piece of plastic electrical tape over the muzzle. But in the field, the tape may peel off in the cold and damp weather. Try this trick instead: Use an oxidizing hand warmer that’s well heated and warm the barrel to aid adhesion. Put the hand-warmer over the tape to make it more flexible.
This tape trick should not affect accuracy, but if that still concerns you, check out the 
latex nipples sold by Traditions. The tiny units stretch, with the ring around the top rolling down the barrel, where it will cover the front sight or just hug the barrel. It’s also excellent for muzzlebreaks, since cleaning snow or dirt from a break can be very difficult in the field.
It should be noted that snow or mud in the end of the barrel is a “barrel obstruction,” and can severely damage your rifle and you. Tape or latex on the outside of the barrel will blow through before the bullet arrives, making it a safe option. Never attempt to “shoot out” any type of debris. Protecting the muzzle is the answer.
Traditions sells a full line of muzzleloading products; check out their offerings at traditionsfirearms.com.
