You are successful. The gunshot rings through the cab, and you see the glass shatter in front of you. One of the bandits falls of his horse, and the gun falls on top of his head. Outside, you can see blood trailing from his chest. The other bandit notices, and looks inside of the cab. He points his rifle at you and attempts to fire.
Fortunately for you, the bullet ricochets off part of the metal outlining of the train. The bandit starts to ride a different way, to the left, and starts reloading.
The bandit shoves the gun to your chest. "I ain't too big for anything. You pull a gun, and you're toast!"