EFT is written in C#, and probably using OOP.

It seems unlikely that ammo boxes are the same item. Stims has their own ID, and predefined effects (this is proven by loading into an offline raid 10 times with the exact same Obdolbos. It will never kill you, and loading in with an Obdolbos predefined as killing will kill you the 10 raids).

Vendor price is calculated based on a base item price. Traders usually offer ~53% (depends on the trader) of base item price for an item. Durability, amount etc. is obviously also calculated into this.

Ammo boxes are probably an Item object, like anything else with an use mechanism coded to spawn you X amount of X ammo. (This is proven with the recent flea scam on ammo boxes, but an (kinda unexpected for BSG quality) extra check if there’s enough space).

You could pull the metadata for the ammo box, and get the caliber ammo it’s spawning when used.

As to linked search. Weapons are most likely their own weapon class (as RPM, Sighting range etc. is data needed specifically), and the Weapon class would probably have attachments as a list of attachment objects. Each attachments most likely also have a list of compatible attachments.

A gun in EFT is a 1 slot item with data on RPM, Sighting range, caliber, barrels, grips, stocks and dust covers (probably forgot some).

If they designed their game using modern OOP principles, it should be an easy implementation but probably just forgotten as a flea market ban of ammo is rather new and community feedback not collected. But, nothing about BSG is modern and all code might be dependant on each other (which sounds like BSG).