IMO, crud rings come from patch lube reacting to the extreme heat, and pressure, in a muzzleloaders barrel during ignition. Mutton tallow, bear grease, and venison tallow, don’t make crud rings because they can handle night heat. Most vegetable oils can be used to season cast iron cookware, because they bond to the iron when heated, and creat a hard coating. They will do the same thing in your barrel.
Hungry Horse