In the chapter Regina, you will reach a point where you are driving your rail car along the tracks. There will be a stationary train sitting on the tracks. You will need to push the train with your car. At this point, you will need to make sure that no Watchers jump onto your railcar. If this happens, you can reload checkpoint and try again. You can switch to military rounds to deal extra damage if you wish, and reload the checkpoint to get them back. As you push the car along the track, turn around and watch for anything that moves. Be sure to reload after every 2 or 3 enemies.
You don't need to worry about anything overhead jumping down onto you, or anything in front of you jumping out. Everything will be coming from one direction.