As stated abobe... broadheads magnify any tuning issues that you may have...

You have to tune your bow to get your field points and broadheads to hit the same spot. You can have an improperly tuned bow.. shoot field points all stacked together... then screw on broadheads and not hit the broad side of a barn. Not to mention... if the insert/broadhead are not straight w/ the arrow... nothing you do will make them group.When you add broadheads.. you are basically putting vanes on the front of your arrow... and if they are not straight.. they will steer you arrow wherever they are aimed. Also the more spin you can get out of your arrow.. the straighter it will fly due to stabilization. Feathers stabilize better than vanes... Helical stabilizes better than straight or offset.