I don't know if you've watched any of those tv shows where they are restoring tanks and other military equipment that has markings on panels that are stamped in. They brush the white paint across the area, and wipe off the excess with a soft cloth, leaving only the paint in the impression. I'd think that would be the only way to do it efficiently on the gun stampings and impressions as well, unless you are some kind of artist and can only fill in the finest depressions of the letters.