Buckshot? Never used it....actually illegal here. I doubt that beyond 20 to 30 yds would be viable.
As far as a shotgun? Many rifled barrels today permit ranges well beyond 100 yds. yardages vary actually with the skill of the hunter. Some i have seen shouldnt shoot more than 10 yards LOL. Others can well beyond that range.
As far as your comment a 50% chance of success? Thats not even a shot to take.