Collars are provided for broadheads. In some embodiments, the collars are shock collars with frangible tabs which restrain the blades of an expandable broadhead during flight, stabilizing the flight path of the expandable broadhead. The frangible tabs break off of the shock collar upon impact, allowing the blades of the expandable broadhead to deploy and increase the size of the entrance hole made in the target. In some embodiments, the collars center a ferrule of a broadhead within an insert of an arrow.