This is a good working spindle mech that I edited from JongeJanssie JongeJanssie. (The one he made didn't work for me)
About this creation
Ok this is a VERY simple but effective mechinism that holds quite a few ruberbands.Everything in gray is the main mech. When you pull the trigger, the force of the rubberband will pull the spindle forward and a part attached to the trigger will stop it like so.
Now when you release the trigger, the force of the rubberband will pull the spindle further, allowing the rubberbamd to fly off the spindle, and then the spindle stops at the top of the trigger, and the sequence is repeated until all the rubberbands are shot.
Now you see this little connector half? This is VERY important. It holds the trigger back so the rubberband that's pulling it won't push it to far. Other wise it won't work. If you don't have a piece like this then use a stud to instead, or a 1x2 lego plate.