I don't think it's a phase

I've been having a lot of trouble with my son. I don't really know what it is. It's been going on for well over a year now. If I tried to list everything I probably couldn't. I'm not sure I really want to. I just know that I'm frustrated. He's very smart. Sometimes I think he doesn't let on just how much he really knows or understands. He's also very sensitive. He can go from happy and laughing to mad and screaming in seconds. The smallest things set him off. If he doesn't get his way he comes unglued. Not just temper tantrum, basic kid stuff. But yelling and throwing things. He's broken his toys and one time knocked a hole in the wall. H started buying him airsoft pellet guns when he was just shy of 5 years old. Now he's obsessed with guns. For the most part he just wants more pellet guns, but it's all he wants for christmas. A BIG pellet gun. It worries me. I didn't like it when H bought the first gun and said so, but I didn't make my voice heard the way it I should have. Now look what's happened. My son has told me that he's going to kill me on more than one occasion. I know he doesn't understand what it means and I know he's speaking out of anger and frustration, but what mother wants to hear that? He just seems to have so much anger and I have no idea how to help him. I've tried to help him tell me what is making him so angry. But it's like he's unreachable when he gets that way. Today I made him an appointment with a psychologist. I know it's more than just low blood sugar (the pediatrician's suggestion), and I know it's not just that he doesn't know how to express himself. He's my baby. I know something isn't right. I have to help him. He's unhappy and I just can't accept that. I have to do something. I have to save my son. You hear stories about these kids that shoot their friends at school and I have to wonder, is this the point where things go wrong? In ten years could that be my son? Is this the point where I lose him? I don't know if it's really that bad, or if I'm just beginning to panic.