Destructible core structure and method for using same

A method for producing a cast resinous part with a complex internal cavity, comprising:

• forming a destructible core structure from a rigid shell configurated as said complex cavity and filled with an inert flowable ballast material;
• positioning said core structure in the appropriate position within the cavity of a casting mold adapted to produce said cast part, thereby providing a casting space the configuration of said part;
• introducing casting resin into said casting space, thereby to envelope said core structure, leaving at least one access opening through said cavity space in contact with said core;
• curing the resin to solidify the resinous mass around said core structure;
• removing the solidified resinous mass from the mold with the core structure in place;
• rupturing the shell of said core structure, and removing the ballast material from the shell through said access opening;
• and
• removing the shell of the core structure from the internal cavity of the resinous mass through said access opening.