why just a half-barrel?

Just thinking outside the box here; is there any reason I can't use a whole-barrel instead of just a half? I was planning on making a standard cast-core 6" dia. riser in a 55 gallon drum going to (2) 55 gallon steel drums end to end partially buried in the floor, covered with cob & rock. I figured the more metal that contacts the mass, the better the heat transfer. Just wondering if there's any potential problems with this.

Hi Dan;    
As long as you insulate below the full barrels . I see  no reason why you can't do that.
I suspect that cutting the barrels is the problem for you.  You'll just need to dig a little deeper.
Keep us posted on your progress!

Hello Dan,    I think one big reason why the half barrel system was implemented because a lot of people don't have the ability to partially bury their barrel in the ground. Most people start with a concrete or wooden floor and build up from there. If this is to be used as a bench, by the time you add an insulation layer, the barrel, then cob (or other thermal mass), your bench height is way to tall to sit on without a step ladder.
The extra room in a full barrel should add nicely to the heat stratification effect.

Why is cutting the barrels a problem? I cut one back on the 4th to make a quick & dirty grill (see attachment). I would just cut one end out of both barrels, weld them together to form a long cylindrical vessel and cut holes at either end for intake and exhaust.