Yeah, definitely possible.

Nobody has asked this before, so there's no guide available - for now there's only an example in code.

Adding new weapons is a little bit more complicated than Vanilla, and has some optional steps for fine tuning.

In general you need to:

1. Create new WeaponType ( lib/weapontype.lua )
2. Create new file at TurretsDatabase folder ( can be copied over from other database file )

3. (Optional) Create custom Barrel type Plugin ( ArmsGenerator/BarrelFunctions & BarrelFunctionProvider.lua )
4. (Optional) Create custom Material type Plugin ( ArmsGenerator/MaterialFunctions & MaterialFunctionProvider.lua )
5. (Optional) Create custom Rarity type Plugin ( ArmsGenerator/RarityFunctions & RarityFunctionProvider.lua )
6. (Optional) Create custom Tech type Plugin ( ArmsGenerator/TechFunctions & TechFunctionProvider.lua )
6. Add new type of weapon to some shop list category ( Balancing/WeaponDistribution.lua )

7. (Optional) Add to drop table ( Balancing/DistributionProperties.lua )
9. (Optional) Modify enemy roles to use those weapons ( Weaponry module: FleetGenerator/Loadouts/Roles/* )

Examples of overriding mining turrets
Xavorion: Mining module contains ArmsGenerator folder and TurretsDatabase folder,
this whole module adds new weaponry generator plugins to override vanilla WeaponType for Mining turrets.

Examples of adding new types of weapons
Weaponry and Upgrades modules have related code of adding new stuff to enemies and shops.