An inflator device including a pressure vessel forming a gas storage chamber having contents including a supply of stored pressurized gas. The pressure vessel forms a gas exit opening at a first end of the pressure vessel. An initiator assembly includes an initiator cover that extends through a sidewall of the pressure vessel at a first end portion of the pressure vessel, such that at least a portion of the initiator cover extends radially inwardly into the gas storage chamber. An initiator is positioned within the initiator cover, and produces a discharge effective to rupture a rupturable closure element normally covering the gas exit opening to allow flow of at least a portion of the gas storage chamber contents through the gas exit opening. A first radial aperture formed in the initiator cover is positioned at a direct discharge distance with respect to the closure element to focus the initiator discharge at the closure element to rupture the closure element. In one preferred embodiment of the invention, the inflator device also includes a supply of gas-generating pyrotechnic material contained within the gas storage chamber, wherein at least a portion of the supply of gas-generating pyrotechnic material is reactable to produce a product gas. A second aperture is formed in the initiator cover, and is in reaction initiation communication with the supply of gas-generating pyrotechnic material.