Pattern density will fail long before penetration fails. If you can restrict shots to 25 yards, #7.5 should be more than enough in a 3" shell. To get 30 yards and up to 40, for best results, a hand load of tungsten 9's, 18 g/cc. Even with the tungsten 9s, you'll want about 100 minimum in the 10" circle at 40 yards.