Looks pretty justified to me. If the maniac survives that, there's gonna be permanent debilitating injuries that will most likely keep him from acting crazy in the future again.
More people need to take heed of improvised and readily available weaponry and tools in the case of an emergency. For example, a car is one of the most potent and active threat stopping devices one has at their disposal. If some psycho is running around with a big knife or rifle and is obviously going after innocent and random bystanders and you somehow don't have a gun at the moment, don't fucking leave your vehicle or do anything like that. Align that mofo up with your lane and give it gas, then let it sit on top of the fuckface. Fire extinguishers are another ad hoc emergency tool. Two pack in one. Blind an active threat and then canoe their heads with the canister. It all boils down to mentality.
seller is A+. Had my stock in hand in 4 days. Crazy lightweight stock too. 
