Here's my 2 cents... I have thrown a lot of lead at paper trying out different chokes. Then I found Clark's (rest in peace) write up and found out I came up with the same thing for my Mossberg. Should have read more books. Kind of depends on your pattern at 40. If it's a really tight pattern at 40, you're going to be throwing a baseball at his head at 20, and most likely shoot over him. Everyone's a little different (think the lord), but I like to pattern just a touch high at 30 with a good pattern, which should take care of 20, and 40 if aiming right below head. Now if you're talking TSS, then 1 shot at 30. If it's a good pattern...DONE. Them things are to expensive to be having fun with!!!