bowtechbloodbother; You will probably find that .665 is a good size to start at. Are you going to be shooting the Winchester #5 lead loads, or heavier than lead?
centaur 1; There is quite a bit of difference between choke tube brands. For instance I haveIndian Creek, Pure Gold, Carlsons, and Trulock choke tubes all in .660 for a 12gaIthaca Turkeyslayer. Shooting the same load out of these chokes, at the same range, on the same day I end up with wildly different pellet counts....we are talking about a difference of more than 60 pellets from the worst to the best.