"...Grizzly Bear defense..." Yogi can run at 35MPH, flat out. He can cover 100 yards in 5.8 seconds. You'll never be fast enough with any firearm. If you're afraid of bears, stay home or wear jingle bells. Yogi will avoid you like the plague.
"...thought the rifled slugs were made to..." Nope. Sabotted slugs are made for rifled shotgun barrels. Rifled slugs are just that. A slug with the 'rifling' on the slug. Really just a big bullet. They can be surprisingly accurate at 100 though. Three inch groups with rifle sights and a C or IC choke isn't unusual.
"...with no rear stock at all..." A shotgun with no stock is, absolutely, the most useless thing on Earth. You have no control whatsoever. You might as well throw rocks. Buckshot, of any size, isn't far behind. Not enough energy or accuracy past 30 to 40 yards. Way too close to even think about using on Yogi.