I have made a couple of them using dog food cans as the internal piping and #10 cans for the external housing. I used wood ash from my wood stove as the insulation and installed three bolts on top to set the pot on.
I tested it by boiling a measured amount of water striaght from the tap which I brought to a boil on my range top. It took 10 minutes 45 seconds to boil.
On the rocket stove the same amount of water atraight from the tap took less than 5 minutes to boil. It used a bundle of twigs about the diameter of a silver dollar and about 8 inches long.
Very efficient and very quick.
If you haven't seen it with your own eyes,
or heard it with your own ears,
don't make it up with your small mind,
or spread it with your big mouth.