Embodiments of an initiator support assembly that includes an initiator housing including an initiator cavity system are generally described herein. In some embodiments, a bridge substrate is positioned within the initiator cavity. The bridge substrate includes a substrate base including a uniform first planar surface and an opposed second surface. The bridge substrate further includes a first bridge contact extending over the substrate base. The first bridge contact is substantially flush with the first planar surface. A second bridge contact extends over the substrate base. The second bridge contact is substantially flush with the first planar surface. The first and second bridge contacts and the uniform first planar surface form a continuous planar mounting surface. An explosive charge, positioned within the initiator cavity, includes a charge mounting surface that is continuously coupled in surface-to-surface contact across the continuous planar mounting surface.