I have a Maxus 26" barrel and I have a Rob Roberts .660 choke, my #'s werent great but ok, 167 in 10 and like 335 in 20" with mag blends. I called Rob and talked to him about it and he is sending me more chokes to try, he did mention that some of those guns really like the .675-.680 but NOT all of them. I am going to do some shooting when they get here to see. He also made mention that some of the magnum blends shells may have more 5's in some lots where another lot could have more 7's, hence the better #'s. I would be careful in getting so caught up in #'s, a lot of people would say that mine are really low and bad, but my pattern is great and we've all killed turkeys before with old lead shells and standard chokes. I would say if you could get around 150 in a 10" at 40 you have plenty.