The time to find out your gun shoots slugs a little wide of the mark is not when the 'buff is 15 yards away and with a full head of steam coming at you. It would seem he can't practice, can't get more than he has, can't get the correct length, and will need more than prayer on his side to avoid meeting his maker in a profound state of pain.
All this complicates severely the "Slugs will stop a 'buff" argument.
Best,
Ted