everyone at school is as well,yes that is a camera phone Nokia 5140i
the trigger has 2 metal wing things right...then i screwed a screw(believe it or not

) into a washer that rotated on an axil point inside this metal "wing" i add a small spring inside so it would be springy

and trigger like, i then glued another washer further up the screw/bolt so it could go further back,and that = more tension which = more power, i use the glued on washer to hook it under a hook you see in the "cocked" photo.the horseshoe nail gets jammed between the washer and screw/bolt when you squeeze the trigger, you let go and it springs shut to hold the nail in place which holds the rubber band, you then hook the washer under the hook at the back which means you dont need to hold the trigger,you then squeeze the trigger again to fire.
woah long post......my main objective was a trigger that worked,i achieved that, my second was that you didnt have to hold it while it has tension(thats why there a hook to hook it under) and my third objective was power which i also achieved.
i can take more pics if need.