Do they want you to do it? No. The fact is, most modern made muzzleloaders can and have been tested to withstand the pressures of normal loads of smokeless. For insurance reasons, they don't want you to do it probably because they don't want stupid people to load 100grains of smokeless simply because they used to load 100 grains of pyrodex. People will do this and they will hurt themselves.

The reason why smokless is NOT reccomended in black powder rifles comes from old muzzleloders? Antique muzzleloaders did not have the quality of metal or the quality of barrell/breach making techniques that we have today. When smokeless was introduced, the old muzzleoaders could not withstand the breach pressures, and I guess the old adage never went away.

This being said. I would reccomend sticking with the manufacterers suggestions or buy a Savage if you want to go smokeless and arguably have the best performing muzzleloader on the market.

Smokeless powder is the original black powder substitute