I usually prefer using a timer for the gun/player object. It's better to config and evolve (if want to evolve the weapon and make the burst longer or faster).
Here's an example I made using the Ghost Shooter template.
https://www.dropbox.com/s/xulbpzmkkgc0r ... .capx?dl=1
Use asdw or the arrows to move, mouse to aim, shoot with left click and burst with right click.
Hope this helps. Cheers!