first off go get some big pcs of cardboard and some birshot. get bout 10-15 yards away and get the poi/poa of the scope dialed in. once its blowing holes through the spot you are aiming at, then back up and pattern..still with a big piece of cardboard or paper..something big so that it will catch all the pattern and you can see what ya got going on and make adjustments, if any. the hevi 13 and the feds will shooot very well through that choke in the 20s.
keep us posted