If a rifle chamber reamer (in most cases) is reground properly, the deminsions should not change. The reason is most rifle chamber reamers have body taper. Thus, when recutting the leading edge of the throat and the deminsions back to the shoulder, you are in fact setting back the reamer and working with larger demisions in which you grind the chamber part to. Hope I made sense of that as it is easier to show than to explain. When dealing with straight wall chambers, yes, you will lose diameter. In a lot of instances, if your reamer is ground to small originally or it is just worn, when regrinding it and setting it back, you can actually pick up a thousand or two on diameter if you want, it just depends.
Hovis