I wonder, if you removed the insulation from the riser and replaced it with the barrel, with a square hole for the riser to poke through and a way to port the pyrolizing gasses back into the burn chamber... the wood to be charred takes place of the insulation around your riser and the ported gasses (assuming the firebrick would allow the wood in the barrel to reach pyrolizing temperatures) would further fuel the flame reaching complete charring temperatures? Just a thought...
