Hello,
As I see cob being presented as a viable covering for the drum, I wonder how much of a necessity the metal drum really is.
From other posts I understood that the main function of the barrel is to provide a steep negative heat-gradient to the inner
chimney pipe. Given materials with high emissivity like, for example, bricks, could the outer barrel not be replaced
by a nice, cleanly masoned, brick mantle topped with a metal plate? The plate could couple thermally with the
inner chimney, the bricks radiate gently and would substantially reduce the risk of inadvertently touching hot steel.