all u will need is a box of k'nex and about 3-6 rubber bands.
really i accidentally made the trigger but so i wanted to share it with all of u.
it is not to bad to make but it can be hard at some parts
Step 1: How to Make the "barrel"
take an orange connector then put a white rod in the center of it then put a white rod in the center two yellow connectors then take the orange connector and connect it like in the first pic and then take another white rod and attach it like in the second pic and then attach two gray rods like in the third pic.