I need to vent and some advice

I just got a phonecall from my mother back in Michigan telling me that they just got done spending $300 at the vet for x-rays and blood work for their little Puggle.  I guess he was just laying around (he is a VERY hyper dog) not eating or drinking and crying a lot. Why? Well...my crazy f**king brother hit him really hard because he poo'ed in his room.  I am beyond seething mad right now.  I love my brother with all my heart but he has some serious anger issues and is growing up to be a VERY dangerous boy.  He's only 16 years old and my mother isterrifiedof him.  To top it all off my stupid grandfather (stepdad's father) gave him GUNS.  =/  They've hid the bullets from him but he is so good at finding stuff.  He constantly finds my mom's vicodin  no matter where she hides them and sells them off.  She had 60 pills on the 4th and now only has 21.  I know my mom, I know she doesn't take more than a half a day at best.  My brother has admitted to selling them before. Sometimes he gets SO angry that he looks like he really could snap and just kill somebody.  He has raised his fists to my mother and threatened me with a knife (he was 10 when he did that). People aren't BORN crazy.  I know its the way he was raised that made him this way.  Its lack of discipline and structure.  He's grown up always being allowed to do what he's wanted and when you try to tell him no...  well it gets scary.  I worry about my mother all the time and every day I am waiting for the call that my brother beat her to death. I can picture the kind of man he is going to be.  The kind that abuses his kids and wife and then is sorry about it later.  Abusers are ALWAYS sorry but they NEVER stop.  My brother constantly exhibits these signs.  Getting angry being sorry/swearnig it wont happen again etc etc.  I couldn't convince my mom to give their dog up.  She loves that dog.  She hardly ever leaves him with my brother but she did yesterday for the first time in a while so she could go do work on their new house.  I was thinking about buying a small safe for my mother to keep the bullets and her medicine in but at the same time I feel that is only helping her by "encouraging" and "accepting" the problem.  I feel like shit when I tell my mother how to raise my brother, but still she doesn't listen.  I tell her constantly that she needs to take the reigns and do something about it NOW while she still can because once he hits 18 nothing is going to stop him until he ends up in prison. =|  I guess I just needed to vent a little bit.  I always look out for myself first but sometimes I regret leaving home so early.  I was afraid of my brother too but I would stand up to him even if it meant getting punched in the face.  He has gotten a LOT worse since I moved out and I feel partly responsible.  My mom is always telling me how she misses me being there because I could talk sense into Lee.  My stepdad is of no help either, he works all the time and is completely sexist.  By that I mean, everything that my brother does he would have beat me for.  In his eyes I am the "bad" child that moved out and is "living in sin", didnt go to college, doesnt have a well paying job..etc etc.  He always tells my brother "don't be like your sister".  But my brother is failing almost every class, has a gf that he's almost gotten knocked up a few times already, he smokes pot, pops opiates...  The list goes on and on but there is no punishment. I am completely powerless.  Do you guys think the safe is a good idea?