Additional Gun Mod Recipes [WIP]

Adds crafting recipes for gun mods like rifled and ported barrels, stocks, scopes, lasers, etc. WIP as all get and needs a ton of feedback on things like:

Recipe source books (current paradigm is main skill texts provide the basic fundamentals, weapon-specific books would probably include things like descriptions of parts and accessories from which you sort of mentally reverse-engineer them, hence the increased difficulty for those ones. Maybe a new book like an army field manual on equipment maintenance or an insurgent's guide to gunsmithing would be better.)
Difficulty levels (I might've highballed them compared to the difficulties for creating other similarly-complex items like revolver shotguns and finger laser CBMs)
Tools and resources required (Kevin mentioned some things like barrels and mechanisms would require a proper machine shop to fabricate, I built these based around the kind of stuff you find in gunsmith stores like welders and soldering irons, swage and die sets, hacksaws, etc so this might only work if we can get machine shop furniture and vehicle rigs set up and additional tool qualities like grinding, sanding, etc)
"Can withstand some rigors" isn't quite the same as "is completely made of
plastic, must be very rigid and be created with very tight tolerances."
What it boils down to is, can you imagine making the item in question out
of low-grade plastic?  I'm agreeing with KA101 and Rivet's inclination of
no.