Mike, as long as you are using a drill with a pilot at the end and it is mounted in a drill press that you have checked for perpendicularity you should be in great shape. I read into your post that you were using a tapered reamer and doing it by hand a definite no-no. I am using a 3/8 inch counter bore with a ¼ inch pilot for my engine and props. One big advantage is that that is what the propeller manufacturer recommended. The pilot is solid around the edges and the counter bore blades cut downward in to the prop parallel to the prop face. It’s a very accurately placed hole. Dan.