Miller, I am still learning the idiosyncrasies of these Boss O/U's, but my understanding is that they were generally set to fire the top barrel first (per mel5141). Apparently Robertson believed that it afforded easier re-loading and ballistic benefits, although those points are certainly debatable.
It is interesting that the barrel walls remain as thick as they measure if in fact original while being ridden as hard as the exterior pitting appears to indicate. Most guns of this era appear to have been more extensively honed.
