To further add that choke is dependent on gun, I shoot an 870 Wingmaster and with a Winchester 3" magnum 00 load the modified choke patterns the best. Your best bet is to get a box of as many different loads as you can afford to try, some freezer paper or something similar that you can shoot patterns at, and go to the range. Try each load with a different choke until you've exhausted your possibilities, then pick the best one and stock up on that load.