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calyx drilling Method of core drilling performed by the rotation of a steel cylinder and cutting with chilled shot, about 2.4 mm diameter, which cuts a formation core. Circulating water carries the cuttings up to a basket-like space at the top of the core barrel. The core is wedged into the barrel and pulled up one barrel-length at a time. Shafts up to 2 m diameter can be drilled, and holes to a depth of more than 300 m.