Chokes are available all the way doen to .640 for your shotgun. We need to know what size shot you plan to use as bigger shot like #4 needs a bit more open choke than #5-#6 to pattern properly without "blowing" the pattern. as rule of thumb I would suggest the tightest chokes:#6-.640,#5-.650-.655,#4 .665-.675 these are in general only and you MUST still pattern not only for pattern but also point of impact as it becomes much more critical as pattern size shrinks.