What type of powder should never be used in a muzzleloader?

Using smokeless powder in a muzzleloader is dangerous and should never be done because these firearms are designed specifically for black powder or black powder substitutes. Smokeless powder burns at a much higher pressure than black powder, which can lead to catastrophic failure of the muzzleloader. This failure could cause injury to the shooter and bystanders, as well as damage to the firearm itself.

Muzzleloaders typically have a design that cannot handle the pressure produced by smokeless powder, making its use not just unsafe but also inappropriate for the operation of such firearms. The other types of powders mentioned, like black powder substitutes, are designed to function correctly within the specifications of a muzzleloader and are safe for use in this type of firearm.