What kind of accuracy gain do rifled slugs give you in a smooth bore? Don't usually use slugs but want to have a box or two just in case. Would I be fine with standard slugs or should I look around for some rifled ones? Primarily I want them for breeching but want some 50-100 yard capability.

Standard slugs are rifled slugs. They're also known as "forster" slugs.
You basically need to use either a forster or a brenneke type slug,which is a plastic or felt basewad screwed on to a wadcutter profiled full bore diameter slug, in a typical smoothbore shotgun barrel. What I believe you're thinking of as "rifled slugs" are usually called sabot slugs. They use a subcaliber lead slug surrounded by a plastic sabot and usually shoot very poorly out of smooth bored shotguns. They should be used in full rifled barrels or rifled choke tubes only. Forster and Brenneke type slugs perform well in all barrels. If you've got a smooth cylinder bore weapon that you need to use for breaching, I'd recommend a dedicated breaching slug for locks,and brenneke slugs for long range accurate shots. If you have a smooth bore with choke tubes and sights, use a rifled choke tube with sabot slugs for both purposes.

I second the nod to the Brenneke slugs.

Quoted: Why breaching? Are you planning on getting locked out of your house?

Shotgun going back in the truck, excellent idea Mike.

I get roughly 2.5-3" groups with Remington slugger and reduced recoil foster slugs at 50 yds with a bead sight.  I am upgrading to ghost ring iron sights to increase my distance.

Has anyone seen or tried the new Brenneke tactical/managed recoil slugs???
-JD