Note; I would not be too concerned whether the gauge had two or three measurement points. An out of round shotgun bbl is most likely to be oval shaped. If you put in a two point tool & rotate 90° & get the same reading it is "Probably" round. On the other hand if you put in a three point tool & rotate 60° & take another reading & it reads the same it is almost of a certainty round. There is a situation in which a "3-lobed" cam can be built which will with a regular micrometer Mike "Round". The same situation can exist in a hole, but not apt to be encountered in a shotgun bbl. I would feel comfortable taking a measurement with either.
