I've used Bore Butter for years in all my muzzel loaders,and never had the first problem with any of them. I have a new Prohunter and since "seasoning" the bore ( I don't like that term,I think conditioning the bore would be a better term) itloads and shoots like a dream. Also you don't have to worry about cleaning it up as soon as you shoot it. I think most that have rust problems aren't getting the bore dry,before applying the BB. I still use Hot soapy water to clean my side lock,but with the in lines I just use solvent(rusty duck) and dry them then apply the BB. No problems yet,after 15years of using it!