Hunting turkey with a shotgun is not an easy task in and of itself. Those Eastern birds you got in Iowa are especially wary. I'd like to see you kill a couple old toms with your shotgun and learn their ways a little before you start chasing them around with a bow. HOWEVER, that said, there isn't anything more satifying than taking a turkey with the bow. If your hearts set on it...best to you and good luck. To aanser you question. Just measure the diameter of your blunt with a rule. I suggest you use a broadhead designed for turkey hunting. I have had great success with the gobbler getter. It is blunt on the tip and the blades are not sharp all the way to the ends to prevent pass throughs.