Theres quite a difference between what folks think is decoying, are the birds flying full speed and swing by to take a look, or feet down at twenty yards. Same with pass shooting. I still think pattern that modified barrel, with the steel shot of your choice, then I think youll have an idea what you thinkll work for you.
I would keep in mind that not all barrel work is just a choke measurement. You can show your gunsmith pictures of the pattern(s) and ask if he can get you where you want to go. From the get go, based on your gun, I figured you are thinking about using relatively small steel shot, and not necessarily the hottest loads. With more info here and there, you may not want to get into significant barrel smithing. Anyway, itll work out.
