T Loy:
I just posted about this on an earlier thread, I know you already have the 20-bore, but I'll simply paste the earlier post in here for interest. Hope it helps in some way.
"Virtually all SxS double shotguns will 'shoot apart' with solid slugs. The exception is the purpose-built smooth-bore slug-gun, the most common being the Sabbati and Ugartechea offerings, and the rather less common Brignoli (..and there may be others).
If you can't find a purpose-built double slugger, the solution is to acquire a robust SxS double in good nick, knock a couple of inches off the barrels, effectively removing the chokes, and re-regulate for your favourite slug load. This is done by lifting the ribs, adding packing around the mid-point of the barrels to 'bow' them slightly, which effectively increases the convergence at the muzzles, then relay the ribs, fit sights, and enjoy!
A Wm Griffiths boxlock I shortened from 30-inches to 26-inches regulated perfectly with RC slugs when the muzzles were brought together at the shorter length and the ribs relaid. Didn't have to alter the packing at all!
BTW, a properly regulated SxS double should not 'intersect' at some specified distance, rather it should put left-barrel shots on the left side, and right-barrel shots on the right side, of a useful composite group at all practical ranges. I would suggest that a composite 6-shot group, consisting of 3 rights and 3 lefts, should fit into perhaps 2 inches at 25yds and 4 inches at 50yds with open sights to qualify as good. Smaller groups are better of course, if you can achieve it.
