[OUTDATED] There is a more sophisticated solution: https://github.com/flipdeezy/SFSE_WeaponModelFOV
You can download the mod also from Nexusmods: https://www.nexusmods.com/starfield/mods/1331
This Repo will not be updated, but remain as an example for anyone trying to do a simple SFSE Plugin.
This is a Starfield Script Extender plugin that is setting up the Weapon FoV.
Extract the WeaponFoVPlugin.dll as well as the weaponfov.ini file into the SFSE Plugin Folder.
e.g. the files should be placed into: C:\Steam\steamapps\common\Starfield\Data\SFSE\Plugins
You can set up your desired FoV value by modifying the weaponfov.ini file.