I have a SBE and have done the same as you BC and am frustrated too. I have purchased 3 different chokes and several boxes of shells and can't seem to get the reults I am looking for. Nothing even close to a 60 yard pattern and like you have settled on 40 yards as max for the loads I have tested. My best is with Winchester #5. The Rem heavy shot didn't do as well even with a special choke designed for it. Federals patterned the worst but did getslightly better thanthe Winchester with the new flight control shells. I did have my gun lazer ported several years ago and wonder if that is hurting my patterns. It actually is supposed to help allowing the end gasses a way to excape eliminating the back pattern from blowing out the leading shot or something like that.