Near the end of a level in a new game with a machine gun (or any fast shooting weapon), hold the Left Mouse Button (or any other button that shoots) until the debriefing screen appears. Then, choose what upgrade you want. Then, hold your assigned shooting button until the screen turns black. Release the button and you should still hear the shooting sound. When you start the next level, you will be shooting without holding the Left Mouse Button. To shoot your gun forever, you must first enable the minnie or flcl codes. Note: It will stop shooting when you click the Left Mouse Button.