I have shot many 870's and I can tell you the 3" guns are all different. I got a buddy whose 3" 870 shoots Win supreme(red shells)#5s like nobodys business with a Kicks GT 640 my gun with same set up sucks. Mine likes a GT.655 with Win Supreme HV(black Shells). However my gun needs a .660 to shoot the Hevi-13 well. If you are trying to save money I would suggest a Hasting choke and the constriction depends on the size of shot and shell you want to use. I would try something around a .650 if I were just gonna shoot lead but more open for hevi-shot. However with the right combonation lead can be lethal at 50yds.....