When you press RB to reload, there will be a clear bar with a small white segment somewhere along it. It will appear where your bullets used to be. There will also be a smaller white bar moving across the clear bar. As soon as the white bare gets inside the white segment, press RB again. This will reload your weapon much faster, and if timed just perfectly, will give your gun an extra boost in fire power. However, if you do not time it correctly, the clear bar will become red and it will take even longer to reload than if you had not attempted it.