Just re-read the article and saw a few different ways to find deminsions; slugging the bbl. with a soft lead slug, slugging the breach end, slugging the throat, how to make sulphur castings for muzzle end and chamber deminsions, and how to make cerrosafe castings of the muzzle and chamber. Author talks about full barrel slugging to find constrictions, too. Sounds like more than one method to me...
