I was standing behind his back while he was cutting it, maybe that contributed to what I have now... But here his steps, he insert a range rod in one end, and a indicator rod in the other end, and then dial in both ends to as little runout as he could get, then the long probe into the actual bore until that was running true. He dial in the outer to get close, and then to a tapered rod to get even closer, and then to the .0001 dial for the final tweaking. There was .004 how much the outer diameter of the barrel was off from the center of the bore, then he pushed every thing fore-ward and recut that chamber.
From what I understand he got at least 40 years of experience... I checked his 25 lb builds on bat actions, they looked great and he also does stocks and custom dies, so it didn't seem like he is newbie in this business...