E350, guess I'm somewhat confused on why you're focused on using a rifled barrel, which, is typically maximized for targets beyond 100 yards and at the same time discussing optics for close quarter home defense?
Additionally, I recommend you research shooting 00 buckshot out of a rifled barrel. While it certainly can be done the rifling tends to spin the buckshot pellets and greatly spreads your shot pattern vice shooting buckshot from a smooth barrel. From what I've seen, with a rifled barrel you get a large donut shot pattern vice a typically tightly grouped, one inch spread per yard from the muzzle, at the same distances.
And as discussed earlier the Brenneke Black Magic bear loads can be shot from either barrel configuration without issue.
If you could precisely describe how you plan to use the weapon we might be better educated in offer advice based on our experience.
Regards