copper sulfate dosent play nice with steel, would the black powder even get hot enough to burn it? If anything magnesium sulfate would be less harmful and will give you a white flame, table salt will give you a sun yellow flame. If it will get hot enough to burn it off, without causing any damage to your guns (I know nothing about muzzle loaders or black powder) I doubt it would color the smoke tho, it dosent on camp fires or from a blow torch.