Abstract: 1. A booster comprising an open ended housing, a propellant charge carried within said housing, a trap assembly interposed between said propellant and opening for restraining said propellant, said trap including an annular ring member, and a plurality of radially extending arms held in disengageable interlocking relation with said ring member, said interlocking arms and ring member being arranged to maintain a rigid assembly upon the application of force from one direction, but which are readily collapsible upon the removal of said force after the booster has been expended.