My conclusion was as follows.
Granite and sharp sand it a very effective way of reducing the length of a piece of copper tube. With barely any appreciable wear on the granite.
The fabrication of a copper tube without solder is impossible.
The casting of a copper tube using primitive techniques is impossible.
As can be seen by Stock's short stubby example which he did not use for drilling.
Had I done my research I would have known that copper tube is a 19/20th century technique. "Drawn copper tube".