Hi Richard.
If a .530 ball will "just" fit the muzzle without a patch, it sounds like the nominal bore size is about .540 (Make sure there is no swell at the muzzle end to ease loading. (But I've never seen Torador barrels with a swell in the bore at the muzzle end). Since it's a smooth bore you will need a ball about 2-3 calibers smaller than the nominal bore size, as you probably know. They do make ready cast balls in both .520 and .526. You could probably use the .520 with a .010 patch. (They use to make a thin .005 patch, but no longer do to my knowledge). Another option: .540 caliber is equal to 20 guage. They make pre-lubed wads and over-shot cards for this size for use in loading ML shotguns. But many smooth bore shooters prefer to load their single ball barrels in this manner versus a lubed patch.
POWDER VOLUMN: I too would not shoot the barrel with 200 grain loads
But here's a thought that just occured to me last night. Do you think you could load say 60-85 grains of FFG powder - and that volumn meet the vent hole ? If so, you could fill the rest of the chamber with Corn Meal, all the way up to the restricted area. Then just load the patched ball like any other muzzle loader. Sounds like a lot of corn meal. But I think that would be better than all the loose wadding. What do you think ?
But I'm still lost on how to properly clean the breech area after firing.
MY BARREL: If it wasn't for the breech cleaning issue, I could simply have the restriced area drilled out, the bore burnished smooth again, and a threaded breech plug installed. And shoot it via the corn meal method per above. Which I may have to do anyway if the barrelsmith can't make a one-piece liner to accomodate both the barrel a larger breech area. But he has been able to fix barrels that I otherwise would not believe he could do.
Rick