All American, all cob rocket stove

Folks, could I ask for advice once again?
A pal is asking for help making a rocket stove for outdoor cooking, I am no expert but agreed.  I was reminded of Glenn and his all cob rocket, pictured below.  Making cob is not an issue.... but I need help on the dimensions, or the ratio for a six inch rocket similar to this one

Thank you, kind stove builders
Rico

6"x6"  feed tube, burn tunnel, and the start of the riser.
Riser appears to be 48"
The feed tube is 16" deep.
The burn tunnel roof should be no more than 10-12 " (wall to wall 22"-24")

The feed in this 6" rocket stove was 12" tall, tucked under the cooktop so it had to allow fuel to be maneuvered into the feed.

The burn tunnel was 18" long total, with a 6" roof. The cylindrical riser above the burn tunnel was about 30 or 36", to allow the cooktop to be at a usable height. The location next to the deck meant that feeding could take place at a comfortable height on one side and cooking could be done at a comfortable height on the other side.

If you have space and height that allow, a 16" feed tube would be nice as long as you can also make the riser closer to 48" from burn tunnel floor. A good chimney will make a big difference in the function of a stove like this.

As my grandfather used to say, "thunder, lightning, great balls of fire"
(He also told me, " here's the only PhD you'll ever need" while handing  me a post hole digger for a long hot afternoon)

Thanks gentlemen, this has been on my list forever and a day, and I have scrap lumber now to pull this off. I have a kick ass chimney in mind. I reckon you are quoting interior inches, not external,  for the holy trinity of feed, burn tunnels and riser, correct? And then the form burns away?
Also, having seen risers in square and even triangular shape, should I accept that a cylindrical shape is superior overall?  I want to keep almost 100% cob if possible

One more query, honest
Would it behoove my efforts to mix the first cob layer with a healthy portion of chopped straw AND some perlite/ vermiculite in the aggregate?

Or better to stick  to straw only for insulation properties, perhaps

Hi Rico,
all of those should be internal measurements, yes.
All cob isn’t going to last forever, but depending on the clay you can make it work for a while.
You will definitely need real insulation on the riser. Maybe cob first and then a more insulative material.  
All cob is going to loose too much heat.

Perlite in the mix for the first layer would probably be a good idea. I would keep the feed and burn tunnel as solid as possible, though, for abrasion resistance. Straw in the outer layers would strengthen the shell for the long term. I built mine with a honeycomb of air cavities between the inner layer and outer shell, partly to economize on cob since I had to transport all of it an hour and a half from the source behind my house, and partly for insulation.

My original construction sat in the upstate NY weather, partly with a flat overhanging lid on the top and later uncovered, for close to ten years, eroding some but still sturdy except for the feed mouth which was most exposed and also weakened by heat burning away the straw reinforcing.