I have a 18.5'' single shot smoothbore shotgun with rifle sights, the sight picture looks like from a Mosin Nagant.
Thats how it shoots at 60yds
with Brenneke Exact 1 1/8 ounce slugs, 6 shots:
The sights are dead on for 60 so I'd expect at least 2 inches of drop at 100 so I would need to aim higher. I guess palm-sized groups would be possible. Remember, the slug loses a LOT of velocity on its way to the 100yd target, I'm not a hunter but I imagine the loss of speed could affect how it performs on the animal.
Oh, and since the gun weighs only 6 lbs it beats the living crap out of me with 2 3/4 shells, and I'm 210 lbs @ 6'1''.