Core

When cannon are cast hollow, after the plan of Rodman, a core is used to make the bore. It consists of a hollow cast-iron pipe, fluted on the outside, called the core-barrel . This is wrapped with rope and the molding sand is plastered over the rope. A water-pipe entering the core-barrel and reaching nearly to the bottom, and another leaving it near the top, are used to maintain a circulation of water through it, thus cooling the casting from the interior.