SKLEP mk1_Shell ejecting Nerf string blaster

Hello fellow nerfers!

This is SKLEP mk1, my free time project I've been working on for the past month.
This is a single firing string blaster that uses (and ejects) Flypoint/ Kirin shells. It fires half length darts. You can still use it without the shells. By the way, the ejection of the latter is somewhat random in power and direction.
Sklep means "shop" in polish, and quickly became my favorite word to say; don't ask why.

Anyways, all the stuff and details you need to know are in the instructions manual as PDF (linked in the files). It includes both the assembly steps and the firing demo.

Before you print, you need some specific hardware parts (not difficult to find):
-about 15-20 plastic screws (e.g. from Nerf blaster)// about 5mm diameter for the head, 2mm for the body, and 15mm of length
-an elastic string, 4mm thickness max // about 21 cm length (before cutting) for a 40kg bungee cord.
-a compression spring of 18x6x6 mm max.
-a compression spring 30-40x6x6 mm max. (I used a