I have not had exactly the same problem that you have. Triple 7, cayugad, and the others have given you some good advice and things to do at the range. Livbucks has been experiencing what we all do when shooting blackpowder, crud on the breech plug or touch hole. This happens frequently when shooting black powder or Triple 7. When deer hunting, you will only be shooting a few shots so it's only a problem at the range. After about 6 tp 10 shots at the range, you have to make sure your cleaning patches are reaching the breech plug and helping to remove some of this before cleaning.

Good luck....

Tom