Abstract: 1. A slot former assembly for use in fabricating the solid propellant in a motor case for a solid propellant rocket motor comprising an outer hollow core, an inner tubular core and a flexible slot former comprising a skeleton frame consisting of stiffening rods that are retained in spaced relation to each other by means of a cord woven thereon in a basket weave and provided with a covering of flexible material operatively connected to said hollow core, whereby when said assembly is positioned in said motor case and the solid propellant is cast therein about said assembly, a slotted cavity configuration will be provided in the solid propellant in said motor case.