Extended Crafting  

Craft gun parts is a simple and not overly expensive process. You start by crafting Resin and Resin Hardener from polymers and oil. After that you can craft Bonded Sand by combining the Resin with crushed sand. Just add some wood and nails to finish the SandMold. Each sandmold will make 10 parts however it will cost you a gun part so you do have to get you hands on at least one of the parts you want.

Craft other needed supplies
Mechanical Parts
Electrical Parts
Acid
Springs
Polymers

Also added wheels to possibly be harvested from cars.