Hi, Balltip!
Welcome to the board!
As for your inquiery for smokeless loads to fire in your double rifle barrels, try looking through back issues of the Gun Digest, in the late 1980's or early 1990's. There were at least a couple articles on loading for large caliber express double rifles. I guess the biggest problem you will have is finding a load that will shoot to the same point of aim. Next to that will be finding standard jacketed bullets that will fit your groove diameter.
The author's name was Taylor, or Jobson, or something like that. He got into cartridge case sources, conversions, and powder/bullet combos.
Where is the Swede gunsmithing school?
Best of luck!