Continuity mistake: The revolver that Snake uses in the film is a 6 shooter. But on the bridge in the end when he gives it to Maggie, Maggie fires the gun at Duke's car 7 times without reloading. (01:27:00)
Plot hole: When Snake, Brain, Maggie, and the President get to the car at the WTC, Snake opens the hood when the car is dead, and somehow he is out in the open when the Duke is about to shoot. First, how would he get there with a crossbow trained on him, and second, how did Maggie pass the revolver to him, when he hands it to her to open the hood of the car? (01:21:05 - 01:21:50)
Suggested correction: When the hood is opened Maggie can be seen immediately putting the revolver behind her back. Being stood very close to Snake it's assumed it was passed to him offscreen. With the crossbow trained on Snake the Duke monologues directly to Snake allowing him to step a foot or so away from the car to look like he's listening and going to accept his capture but ultimately it was to have a shot at the steam engine and create a distraction. Maggie took out the crossbow guy by slamming the hood on him.
Suggested correction: She only fires 6 shots. Watched the scene 3 times. Only 6 shots.