RE: Rifled slugs... how accurate?
It really is a crap shoot sometimes. My Mossberg 500 would only get around 4 to 5 inch groups at 50-60 yards regardless of what choke or ammo I used. Now my Browning A5 would get 3 inch groups at 100 yards with winchester super X rifled slugs. Both guns had adjustable clamp on fiber optic sights. And oddly enough both gun shot better with a modified choke than they did with the IC choke.
You just need to do some experimenting and see what you get.
Paul