[mrerick]

David, thanks for your coherent explanation.

Gun steel is softer than we probably would like to think...

Halos are also caused when the blued steel surface is stressed and physically moved as the die plows into the steel displacing the metal structure around the places the die pushes into.

As the blued surface is plowed, the very thin areas spread apart in the process look lighter because the silver steel is pushed to the surface making the blued magnetite (the black oxide state of iron) thinner.

Those high spots are also more subject to abrasion wear, as David says above.

Should the numbers on the barrel have halos? That probably is most dependent upon whether the barrel is blued before or after the digits are stamped into the surface with the dies. Stamp the metal, then blue it and the bluing will be uniform. Blue it before you stamp it and you'll get halos.

It's probably possible to crudely fake halos by lightly applying chemicals that destroy bluing like "Iron Out" or "Naval Jelly". if that has been done, only very close examination of the area will help you determine if the bluing is real or faked.