29 grains of Blue Dot under 1 5/8 oz of shot is a lite powder charge. Most listed loads with this shot charge in a 3" hull using Blue Dot are around 38-40 grains depending on exact hull, wad, primer etc. Sounds as if Buck may be following the old W Greener axiom, Little Powder, Lot of Lead, Shoots Far, Kills Dead. It certainly doesn't appear though that Buck is Babying his Smiths. Was this gun originally chambered for 3" shells??
I do recall reading an account once of Buck taking an old beat up Hammer Smith, rechambering it for 3˝" shells. He began with maximum loads using Blue Dot & went up from there. He quit when the gun began opening itself with every shot but did not succeed in breaking anything. Most of these old American doubles are pretty Tough old Girls, with the biggest concern usually being the Wood.