The only kind of powder that should be used in a muzzleloader is black powder or approved black powder substitutes such as Pyrodex. Modern smokeless powder is not safe for use in muzzleloaders and can cause serious injury or damage. Black powder is the traditional powder made of potassium nitrate, sulfur, and charcoal, producing a dense cloud of white smoke when ignited. Approved substitutes offer benefits like less corrosive residue but should still be used according to guidelines made for muzzleloader safety and performance.