So sorry that your difficult child is making some bad decisions.
How is he gambling, at school, or online? Can that be nipped in the bud by some restrictions? I have to say that is an awful lot of money to make gambling for a kid, just curious how he went about doing it. My first thought when I read your post was that he had stolen it. I guess it is good that at least that did not happen.
Has he made references to his weapons as if he has intent to do something harmful? Or does he refer to them as collections? I mean, on the hopeful side, some kids just like weapons, but never have an intent to do anything with them. Not sure of your history, but just thought I would throw that out there.
I hope he is at least able or willing to see a therapist, and that he/she can help with all this. Sending best wishes your way.