An image capture method is provided. The apparatus contains a wettable filter medium for use with a respirator in order to filter tritium, the filter medium being wetted when in use. The hand guard extends over and surrounds the barrel. In particular, an upper pin of the firing bar longitudinally moves through an anvil slot and a channel slot is captured between a lower cap and a middle pin of the firing bar to assure a minimum spacing. A remaining portion of a slant mark formed by a plurality of scale lines arranged in parallel to each other is formed between the remaining portions of the alignment marks.