What is what powder is the only kind that should be used in a muzzleloader?

Only black powder or black powder substitutes specifically designed for use in muzzleloaders should be used in a muzzleloader. These powders are designed to burn more consistently and reliably in a muzzleloader, which can help ensure proper function and accuracy. Using other types of powder, such as smokeless powder, can be extremely dangerous and potentially cause serious injury or damage to the firearm. It is important to always follow the manufacturer's recommendations for powder type and powder charge when loading a muzzleloader.