Several years ago when Brenneke brought back the 2 1/2 in. slugs I bought several boxes to test in my, at that time, 4 drillings. All were pre-war with the newest being from 1936 and the oldest between 1891-93 and WWI.

The Brenneke's did not regulate in any of them, which should be no surprise as all had open bore right barrels and choked left barrels. I don't remember that any shot remotely to POA at 50 yards. At 25 yds. one or two could have been used, barely, as they shot what could honestly be considered a group but, a good bit away from POA. The others threw the slugs willy-nilly.

I know of a couple gentlemen who have double guns or drillings that shoot them to fairly close POA but I don't know of any that regulate, as I would consider regulation. That certainly doesn't mean there are none out there, just that I'm ignorant of any.