Abstract: An apparatus for generating a large perforation in a target such as a wellbore casing. A liner is positioned within a charge case lowered into a well. An explosive material is initiated to collapse the liner to form a material penetrating jet. A spoiler is positioned proximate to the liner to defocus the liner collapse. The spoiler forms a hollow center in the material penetrating jet and concentrates the energy of the jet into a large annular ring for penetrating the target. The spoiler can comprise a passive spoiler which blocks the full collapse of the liner, or can comprise an active spoiler incorporating a high explosive or an elastic material for counteracting the liner collapse. The spoilers can be spherical, cylindrical, tapered, or another shape to modify the configuration and performance of the material penetrating jet, and a spacer can retain a spoiler in a selected orientation relative to the liner.