The gentleman (KY Jon)is not really full of hot air. I have used machinist made 10 to 12, 8 to 10, and 8 to 12 chamber inserts for many years. Today, the better idea is to use store bought inserts, but they are a fairly recent development. My assumption is that the machinist made inserts were not made from bar stock, but from tubing that was as close to inside and outside dimension as the machinist could buy it. The person who made my inserts in various sizes was a bit secretive about his methods.
