I'm not Jim but even if the barrel nut face was .020" off of perpendicular to an axis drawn through the center of the nut it would not generate enough force to stretch or otherwise damage the heat treated receiver ring.
Such a deviation from perpendicular would however set up uneven tension and stresses which would affect the vibration pattern of the barrel with potential adverse consequences for accuracy.
Ideally you want everything making up the barrel/receiver ring/barrel nut interface to be as perfect as possible so as to set up even pressure 360* around the barrel. This will allow the barrel to vibrate (whip) at it's natural frequency without any influence from the nut.
Bookmarks