If you are porting AI body and head models in to a older cod, for example zombie models into cod5.
Many people have reported that the head model dose not detect bullets meaning you can’t shoot them in the head.
The fix for this is very simple and easy, what you have to do is set a hit box model to a model that includes a head, otherwise the head area is not part of the hit box.
You can pick any model as long as it is full body and includes a head, the number of verts it has is not important since a box is calculated around the mesh, the mesh is not used directly.
You define the hit box model in Asset Manger under the hit box section of the model.
The one I used: american\characters\Roebuck\char_usa_marine_roebuck_fullbody.XMODEL_EXPORT