The tech adds a recipe that doesn't exist it seems.
8.417 Error ModManager.cpp:1767: Error in assignID: recipe with name 'casting-railgun-ammo' does not exist.
Source: casting-railgun-ammo-tech (technology).

Sorry for the late reply. Can you tell me your mod settings? Did you change them? Aside from that, that's a solid report. I'll look into that tonight.

Default settings reset from loading error, loaded only this mod and the library.
This mods version is 0.8.3, assets is 0.3.2.

Hiya, just tried 0.8.5 and the recipe still seems to be missing. The tungsten railgun ammo exists so maybe it's an old attempt you changed?

Both the normal and tungsten railgun ammo should be there, normal and foundry recipe. I still have trouble with reproducing this bug, therefore it is very hard to fix it.
For the next version, there will be a broader debug option so that I can better see the exact issue. Thanks for your patients.

Found the issue, it was another mod changing the recipe category so I'm assuming breaking the generator. Its https://mods.factorio.com/mod/em-foundry-expansion.

Great, that would explain why I couldn't reproduce the bug myself with a very clean version. So I recommend that you use my other mod (https://mods.factorio.com/mod/OCs_foundary_expansion) as it is intended to work in combination. It seems that it has some overlap to that other mod. It is also AAI and K2SO compatible.