I'm not good with remaking meshes and hopefully someone here can do this. The autoaxe's mesh does not match the 2handed automatic melee attack animation that new vegas uses. The autoaxe's blades are to the left of where the game's crosshair is located. This results in the weapon hitting too far to the right (i.e. it is really wierd to see the spinning blade hitting the enemy but the blood effect/damage is actually to the right of the blade, where the crosshair is located).
Looking at the chainsaw's mesh, the devs used the autoaxe's body but put the blades to the right to match where the cross hair is located. Since i'm not good with blender, I hope that someone here can remake the mesh so that it is repositioned correctly with the animation that new vegas uses.
