If weapon will be made from parts.
You will have to maint tain your firmarm by 4 items
oiling kit will be avaliable solution from 99-90% condition
Calibration tools - 90-60%
Tools for fine work 60-30%
Tools for basic work 30-0%
If weapon will be made like in 3.0
you will have to find/craft/salvage parts(not metal scrap) from other guns and apply them to other guns.