rfrankhauser,
In general, except for a few "bespoken" ones, drillings were made( therefore "regulated") without any scope or mounts. Some very recent drillings were made with provisions for mounting scopes, but these are not the ones we are discussing. The sights were adjusted (filed) using one particular load, that may or may not be available now. They were regulated at an available range, which could have been 60, 80, or 100 meters. I suggest you try the slugs at a longer distance. You should shoot from cold barrels, drilling barrels are known to be very stiff and stable. However when one barrel is hot, it elongates and shifts the point of impact(worse with sxs combination barrels). When you get the drilling sighted in with whatever ammo, sights, distance, and POI you choose; you are pretty much stuck with wherever the slugs shoot. If you insist on using the slugs, the best you can do is find where they impact and learn to "hold off". In my own drillings, I usually have small shot in the left shotgun barrel, an einstecklauf ( insert barrel) in the right, and the large rifle; so I don't worry about slugs. FWIW, with an o/u combination, by "holding over", I could keep Brennekes (67.5mm case length)in a hat size group at 100 meters, and still loaded shot in that barrel.
Mike
