That is a bad assumtion the reason is the same as why you can not shoot smokeless powder in a muzzleloader .
With out the brass cartridge case to expand and seal the chamber expanding gas at 55 or 60 thousand pounds per sqare inch will cut its way right out through the breach plug threads.
There are several muzzleloaders on the market designed for smokeless powder and they require a great deal of care to be sure they are not overloadedthat is as close as it has come to what you are talking about at this time. Lee