I would try the Winchester Long Beard XR shell in #5's with a .665 choke. Same shell for 6's I would use .655 or .650, I have never shot 6's other than patterning them years ago and out of the .665 choke (I tried numerous other smaller Hasting chokes, never panned out) they were kind of thin at 40 yards, plus #6 shot would be stuck in the cardboard backing at 40 yards, never the #5's. Guns I used were 870's, SPST 3" and Super Mag 3.5 inch, Using Winchester Supreme High Velocity 3" and 3.5"