He could have stopped the boss guy on the train so easily.... spoiler
he brings no gun on the train, then kills 10 guys with guns, (2 he actually shoots).
after that fight he walks a short distance to the next cart and "I can't get any closer to the boss man (wrist bomb)... why didn't he bring one of the ten guns on the floor" so he has to drive the car to the next train cart doing some crazy dangerous stunt...
Why would a guy who uses guns and has guns in his poster not carry one of the free guns with him to stop the boss.