The Feds do regulate some muzzleloaders, but it is not because they use shotgun primers, pellets, or sabots.
The Feds consider a muzzleloader to be a modern firearm if it can be easily converted to shoot modern metallic cartridges.
Thus, the TC Encore with a .50 muzzleloader barrel is considered a modern firearm. The TC Omega, which shoots the same ammo and primer, is a muzzleloader. The Encore is designed to interchange barrels with a number of modern centerfire barrels, thus the Encore receiver would need to be shipped to a FFL.
The Savage, which shoots shotgun primers, and smokeless powder, is considered a muzzleloader not a modern firearm.
Sorry I don't know how this relates to the Scout, don't know what that is.