Disorderly conduct and disturbing the peace are catch-all categories, IMO.
Sometimes they can be pretty hard to beat.
It's usually a misdemeanor and 50-100 bucks, something like that.
What I think is tricky about this one though is that it's firearms related and I wonder if it ends up hurting him if applying for non-res permits in other states.
If I remember there are some states that ask on their forms if you've ever been charged with anything related to firearms... I'd have to go and re-check every application again to see what questions they ask.