RE: how far can you shoot a 12ga rifleed and non rifled barrel
Depends on how well you shoot and how the gun likes the slugs. I have seen smooth bore guns that shoot well enough to kill deer at 100 yards in the right hands and fully rifled guns with expensive slugs that are not accurate enough to kill one past 75 yards.
As a general rule I would agree with bigcountry's post though.
I know my A-5 with clamp on sights and a smooth bore with the right slugs will group about 4 or 5 inches at 100 yards if I have a rest. Rifled slugs are good to about 100 yards in my opinion if you get them there accurately. Modern sabot slugs are good ballistically out to around 200 yards if your gun can shoot that far with them (good luck on that). Again my opinion nothing more.
For the average joe I would say rifled barrels with sabots are a 100 yard gun, with either scope or open sights depending on how well you shoot and can see. And smooth bores with rifled slugs are usually a 50-70 yard deal, providing you have sights on it.
Paul