internal defects which it is estimated will not be corrected during the detonation of subsequent stages without modification of the charges are noted on the outside surface so that supplementary charges may be added in appropriate areas the second stage comprises eight charges formed by strips bs and bl of detasheet sheet explosive of the same respective dimensions as the strips as and al but applied to areas of the short and long outside surfaces of the sleeve inwardly of and abutting the areas to which the strips as and al were applied the stage also includes any supplementary charges judged necessary after as a result of the examination which followed the first stage the third stage also comprises eight charges formed by strips cr cs and cl the strips cr are 5 7 cm wide and are applied to the corners of the sleeve so as to cover the areas between those covered by the strips as and al and the strips cs and cl are respectively 5 7 cm and 6 9 cm wide and are applied to the areas of the short and long outside surface between the strips bs and between the strips bl the third stage also includes any charges required to correct defects in the inner surfaces noted during examination of the sleeve after the second stage and not expected to be corrected by the charges cr cs and cl if any portions of the interior surface remain insufficiently formed after the third stage suitably disposed fourth and subsequent stages may be utilized until the desired result is achieved.