4seventy, yes I agree that the re-marking can be done without apparent evidence - but usually only if the entire barrel is refinished. If it is a simple re-chambering that doesn't require outwardly marring the barrel it would be very difficult to blend the metal so as to be unnoticeable and the degree to which cold blue would be applied to this large area would not be best. Additionally, to properly blend the contours, any other nearby desirable markings would likely be lost with the caliber designation. On the other hand, a (very) small "flat" with the new markings is not terribly distracting and requires only a very small application of cold blue.