I have used a lot of Pyrodex as well and never had a problem? I have one rifle I bought in the eighties and it is all that has ever been used in it and the barrel is fine? I use water, soap with patches made from old tee shirts. I lay the barrel over two burners on our cooking range and get it very hot to drive away moisture. I then use 3in1 oil and wipe the bore real good. The next day I run a patch down the Barrel to remove the oil and reoil it! If I see the least bit of rust I will run multiple patches down the barrel and re oil again. I think it is lack of cleaning or waiting to long to clean that is the problem. Black powder will cause a barrel to rust if not cleaned as well.