V. 1.2= there are mods to make it hold more rubber bands, I don't have pictures, but I did try to make it as clear as possible to what you do.
V. 1.3= there is a mod for full auto, it is not that useful though, considering they all shoot at once. someone will find it useful though.
Step 1: Parts list
to build version 1.2 you need another white connector and 8 white rods
to build version 1.3 you need two less green rods