The correct answer is that gas masks are not considered ammunition residue.
Ammunition residue refers to the remnants left behind after ammunition is fired. This typically includes materials that are physically associated with the ammunition, such as empty cartridge casings, which are the metal shells that remain after bullets are fired, and spent bullets, which are the projectiles that have penetrated their target or otherwise been discharged. Fired ammunition boxes, which may contain traces of powder or other residues, also fall into this category as they are associated directly with the ammunition itself.
In contrast, gas masks are personal protective equipment used to shield the wearer from harmful gases, vapors, and aerosols. While they may be used in environments where ammunition is fired, they do not incidentally contain remnants of actual ammunition, therefore they do not qualify as ammunition residue. This distinction is crucial for understanding material safety and contamination levels in various military and operational contexts.