The smokeless MUZZLELOADER barrels are fine on any frame. Unlike a rifle barrel the muzzleloader barrel has a screw in breeech plug that contains rearward pressure.
The problem you have when shooting rifle barrels from shotgun receivers is rearward pressures from the cartridge case are much higher (the case pushes back on the face of the receiver around the firing pin), that is why they put the SB2 frames through a special process which hardens it. This hardening proceedure minimizes the possibility of frame streach.
That barrel has been intriguing me for over a year, Michigan regs (for deer hunting) are the only thing keeping me from buying one. I have thought about getting one for messing around on the range with and I could still hunt other things like 'yotes with it! Gets those wheels a turnin' evertime I see it. I am just not sure about the 1-36 twist, but it is a Douglass button rifled barrel! :grin: