Turning a blank and coming out with a good product can be risky. If the smith does it extremely slowly, as in stop when it begins to warm up a little and waits until cool to start again success is sure. Very, very slow to do. I would recommend a pre-contoured pipe that the manufacturer has properly stress - relieved after contouring and/or fluting. Might as well remove that variable on you quest for the ragged hole. Of course there are many success stories to the contrary, your individual mileage may vary.