There is a good reason why nearly all sabot ammo is marked "for rifled barrels only".
It's because they are made for rifled barrels only!
You didn't mention, or I flat missed in your post, if you have any choke at all in your smooth bore?
If you do and shoot saboted slugs you most likely won't have any choke left and you could just split
the muzzle end of your s.g.
I can't say I that your accuracy standards are very high.
A stop sign, most around here anyway, is a whole lot bigger than the kill zone of any bear I ever heard tell of.
Now maybe if you are concerned about running into T-Rex that standard might be applicable.
Thre is snothing wrong with your smooth bore s.g. for bear protection. In fact everything right about it.
You just need the correct ammo for your barrel.
What is it your shooting anyway?
If it's a 12 bore with modified or less chock then the Brenneke K.O. is about spot on for your purposes.
Listen: I've killed over 50 whitetail with the older vesrion of the Winchester 1 ounce dead soft foster (rifled slug).
Ballistics are 1500 f.p.s. at the muzzle for the 437.5 grain one ounce near 3/4 diameter lead bullet.
Than traslate into more whoooop-butt than you can imagine in the real world.
If you are really concerned about stopping a critter for having you for lunch a Brenneke, because of it's better construction, is your ticket to keeping your skin in one piece.
The K.O. is:
Now if you are really serious about stopping a critter intent on causing you intense emotional upset scroll down to Dixie ammo, a sponser on this site, and order at least 5 boxes of that locomotive stopping ammo.
is the BEST in it's class.
Also check out Dixie Tri-ball loads. Awesome!
Five boxes is 25 rounds which should enable you to pratice with at least 10 or 15 rounds and keep the remainder to stop T-Rex.
By the way. You can't shoot the s.g. without sights any better than you can a hunting rifle without sights.