Just an idea: It would work a lot better if another option to switch weapons is the scroll wheel, because it is much faster and all ready at my finger tips.
Tips: To use your missile's press the space bar, and also with your cannon when you reload there is that green bar if you click when the marker gets to it your shots will do more damage (cannon only), the Machine gun fires faster when it's in the red.
Scroll wheel change, on its way.