What should never be used to propel a bullet from a muzzleloader?

The correct answer highlights that a muzzleloader should only use black powder or recognized substitutes specifically designed for such firearms to propel a bullet. Traditional black powder is a specific formulation that ensures the proper functioning and safety of muzzleloading firearms. Using any substance outside of this clearly defined category can lead to dangerous situations, such as excessive pressure or failure of the firearm, which can result in injury or damage.

In the context of muzzleloading, it's critical to stick to established materials, as these have been tested for compatibility and safety. Muzzleloaders are designed with specific tolerances and characteristics that are geared towards black powder. Other substances, including those intended for different firearm types, can behave unpredictably in comparison.

This understanding emphasizes the importance of using the appropriate materials when engaging in muzzleloading for the safety and performance of the firearm, as well as adherence to legal regulations concerning firearm use.