Tatwell:
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 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.
Mark, regarding your recommendations on using flechettes, I respectfully suggest that you should probably be locked up.
