Batman is pissed off because his super sexy alien girlfriend cheated on him with Super Man. So he got angry and turns into a blooslusted monster and decided go to a zoo murder the baby polar bear above ^^^^^^^. You are watching the scene while Batman kicks the hell out of the security officers and the zookepers. You have your gun and i'ts the only thing stepping between Batman and the death of the cutness of the baby polar bear. But would you live after you know you killed the only guy who can stop the majority of the criminals, assasins, vilans and rapers of Gotham City just to save a life of a poor bear?
What happens next?
If Batman armor is bullet-proof then you can choose between a .50 BMG, a M16 or a bazooka/rocket launcher.