The key to the driver is a slight undercut, so that you do not flare the top of the guide or get the driver stuck in the guide. A hand ground one can easily hurt the guide.
I hate dragging carbon thru the head, so I often drill the top of the guide mostly thru, then break top of guide off at snap ring.. Then. Remove into the port if there is room.
Then you are not dragging carbon thru the guide bore.