All the years I have owned and shot muzzleloaders, the one that gave me a fit was a T/C Renegade that all I used (was told the story of you have to season the barrel) was bore butter. The accuracy got so terrible with it that I could no longer rely on the rifle for hunting, and forget target shooting.. that was a joke actually. I then used boiling soapy water and a bore brush and welding gloves to hold the barrel as it got that hot. After a lot of scrubbing I started seeing chunks of brown stuff in the water that I was dumping. I am guessing it was bore butter that had rust or fowling with it. Since then, I continued to scrub the barrel with soap and water and a bore brush, but after that I dried the barrel then alcohol swabbed it, dry patched it then used a quality gun oil in it.

The original Renegade barrel that went bad came back to normal after a good cleaning and re sighting in. This same barrel I am now conducting a bore butter test with according to Roundball's method of barrel cleaning and treatments... I have to admit, I am shooting it and it shows no sign of rust, and the accuracy is fine, but then I remember the other one took years before it finally went down hill on me, so time will tell. The one barrel gets bore butter the other rifles get Birchwood Casey Sheath....