Look up Elm StovesI had a metal fireplace with the sharp angles of the rumsford design. Not something to be used to seriously heat with but darn, I loved that thing. I can see where a barrel stove would be useful.
It does make you wonder what is possible with a heavier steel and angles. I'm wondering if a barrel could be converted to a fireplace by installing angled panels on the interior. Maybe even filling in the gaps between the barrel walls and panels with mass...just some thoughts running through my head.