The other thing on your bow is how much of a shielf you have. The deeper the shielf is cut towards the center of the bow the more forgiving the bow will be with stiffer arrows. Are your arrows spined 60-65 or 65-70 as it isn’t very often you get a set were all of them are dead on to the pound. I have built some set that are dead on but you have to sort through a bunch of shafts to find them and it is very costly. From your symptoms it seems to me you may have a few problems. Have you tried paper tuning your bow and arrow combo? If not I suggest you try this and work on one problem at a time. Porpousing is mainly caused by a nock height problem and fishtailing is a spine issue. If you combined both of these then you can get a flight that looks something like the corkscrew you described. Your arrows may be very close to the right spine, but some of them because of the normal 5 pound spread could top over as being stiff, or bottom out at being weak. Hope this helps some, with more information I can help you better.

Derek