In productions with weapons the Armorer, a.k.a. Weapon Master, usually has a significant role -- certainly on par with other credited parties (like personal assistants, caterers, wranglers, animal handlers, etc.). But I haven't ever found the armorer in the credits. Why is this?
An Armorer isn't listed in the credits because it's not a role/job title in the movie industry.
Weapons are props and, as such, are under the guidance of the prop master:
This job description varies somewhat from country to country. In the United States, food styling, weapons and animals are often directly or indirectly within the property master's domain.