A modified fluid delivery cartridge. A conventional straight-sided high pressure cartridge case is primed and then filled with solid propellant. A burst cup is inserted in the case mouth. The burst cup is preferably embossed with a cross or other shape to promote predictable rupture. A charge casing is provided which opens into a high pressure cartridge receiver bounded by an inner charge casing wall. The inner charge casing wall is provided with a step, in which the diameter of the high pressure cartridge receiver is reduced. The high pressure cartridge case is pressed into the receiver in the charge casing wall. As the high pressure cartridge case is being pressed into place, the straight wall of the case passes over the step in the inner charge casing wall, which deforms the straight wall to form a neck. This neck captured the burst cup within the high pressure cartridge case.