Your son should see a professional therapist so that he can have a forum to say what makes him so angry, frustrated, and neglected that he feels compelled to say he wants to be dead. I am sure it's clear to you, your husband, and any other family members and friends that your son should never be allowed to have access to any firearms. We tend to think that young kids cannot feel severe depression and/or anxiety, but they can. Your son must learn how to cope with his anger and frustration in more positive ways, from a position of optimism. This classroom declaration suggests that he is looking for help with some emotions that overwhelm him.
I would also take inventory of any major events that have occurred in the family (e.g., death of a family member) that might have led him to be more despairing. Please get him the experienced professional help that he needs and make sure that this family-oriented therapist includes you in the therapeutic process. Tackle this as a family problem, not your son's difficulty.