John- The strength of the barrel or the receiver is irrelavant, the reason smokeless frag's BP arms often killing or seriously maiming the shooter and anyone foolish enough to be nearby, is that smokeless powder is not designed to be used in a vented environment period.
I also think that if you take the time to learn how to use and appreciate real Black Powder you'll find it's a truly wonderful propellant with many advantages over smokeless, not to mention the type of firearm you're talking about has definative limitations that make the use of smokeless in it totally irrelevant.
The only real advantage I can conceive of in shooting smokeless in a Muzzleloader not specifically designed for it, is the Darwinian aspect of gene pool improvement, and it can be extremely lucretive for the surviving family members as even though the tragedy was completely the result of idiocy on the part of the shooter, juries will often award huge financial settlements to the estate, because the manufacturer didn't find a way to make it impossible for the victim to perform the fatal act.
fredj