Can't comment on your link.

Large shot was and still is used a lot in France. Joel Dorleac recently posted an old vintage image elsewhere of a group of French hunters with a bear, boar and either a hind or? All carrying side by side shotguns. He replied to me they used shotguns and large shot.

Someone once commented that a lot of French hunters still used shotguns for drives for boar and deer. Large calibre rifles are rare.

Using your shotgun with ball or brennecke? Try it and see. I've used breneckes in a friend's semi auto shotgun in past days.

One idea regarding regulation. If you can shoot one barrel accurately or reasonably with ball or brennecke, and use SGs or SSGs in the other barrel it will work fine.

. Nice to be able to use ball in both barrels of course.