Using which type of powder in a firearm not designed for it can be dangerous?

Using smokeless powder in a firearm designed for black powder creates a significant risk. This is due to the vastly different combustion properties of smokeless powder compared to black powder. Smokeless powder burns at a much higher pressure and temperature, which can lead to catastrophic failures in firearms not built to withstand such forces. Firearms that are specifically designed for black powder have components that may not be able to handle the increased pressures generated by smokeless powder, potentially resulting in explosions or other serious malfunctions.

In contrast, black powder is specifically formulated for use in traditional muzzleloaders and is safer in these contexts. Granulated powder and powder with additives can also pose risks depending on their specific formulations, but these choices do not have the same broad incompatibility issues associated with smokeless powder in black powder firearms. Thus, using smokeless powder in the wrong type of firearm is particularly dangerous and should always be avoided.