Knex Cannon

I need help i need a trigger for my first knex cannon i will post instructions and give credit plz give help tips and ideas in comments

Step 1:

Rubber party balloons as rubberbands and decent power

Step 2: Update

Ok trigger added plus other mods

How to work add this to rubberbands(first pic)

Add this (second pic)

Pull back and latch black peice onto white snowflake (pic 3+)

Push blue rod to left to shoot (last pic)