Of all the words you listed, I prefer the following three:
aficionado, fancier, and loony,
and I see nothing wrong with loony (definitely better than zealot or fanatic in terms of PR with the general public). Although I might prefer to be called a fancier or aficionado, I think "rifle loony" is more descriptive, and isn't that what writers are supposed to find -- colorful, descriptive terms to describe their topic?
