RE: broadhead flight?
65# at 31 inches? What is the speed on that, 320 or so? Anyway, broadheads are going to have somewhat bigger groups just because of the increased area for aerodynamic drag and the slightest crosswind will have a much bigger effect than one would think. I did a study on it in college and was amazed by the results. Also, the rotation of the blades will create some lift that changes things. If it is only one arrow though I would check to make sure it is not the same arrow every time. Then check the shaft and the broadhead. It is not uncommon, in my experience, to have a broadhead shaft (whatever it is called) a little crooked. A simple spin test can show you if it isa little off. Again, it is amazing what a rotating imbalance will do to arrow flight.