I am not the expert here, but what I did was go buy a packet of 100 yard targets, and I set up a backstop and measured out in my case it was 38 yards. Have a rest, if you don't hold as steady as you can, aim in the middle and shoot one shell, and then change the target and keep goign that way until you have tried all your combos.

A 8.5 X 11 paper works also. I used this last night to finish up my pattering. the final results for me is Full choke 3.5" BB and 3" 2's I tried the BBB in the full choke and only 4-5 BB's hit the paper. #2's were all in the center. Modified choke I can use 3" BBB and #2's with BBB being best.