Failed to load mods: ...Ammo__/prototypes/items/SE/vulcanite-rounds-magazine.lua:19: attempt to index field 'action_delivery' (a nil value)
stack traceback:
...Ammo__/prototypes/items/SE/vulcanite-rounds-magazine.lua:19: in main chunk
[C]: in function 'require'
...astBullets__/recipes/more_ammo/cast-vulcanite-recipe.lua:1: in main chunk
[C]: in function 'require'
ICastBullets/data-final-fixes.lua:14: in main chunk

What mods do you have installed and what are your mod settings?

Its probably incompatibility with More Ammo mod. Maybe just check if that field exists?

...Ammo__/prototypes/items/SE/vulcanite-rounds-magazine.lua:19: attempt to index field 'action_delivery' (a nil value)

The problematic line in vulcanite-rounds-magazine.lua is

source_effects = data.raw.ammo["piercing-rounds-magazine"].ammo_type.action.action_delivery.source_effects

and I am not sure why ammo_type.action would be nil. I will continue to try and fix this, but as of now I have no idea why this would happen. Another thought is that maybe you're using an old version of More Ammo?

Using the latest 1.5.20 version thats available on Factorio Mods.

Hm... Interesting. Any other mods that may modify recipes/technologies?

here https://gofile.io/d/xSSp1X

I don't see anything that would change the source effects of piercing rounds, which is weird. Could you also upload your factorio-current.log after you load the game and it crashes? It may be able to provide some more information on why its crashing.

https://gofile.io/d/Qlwwm4

I have made a change to the mod, but don't want to fully publish it to the mod hub. This is the updated mod. I suspect that it may still crash, but I am unsure so if you could test it and see if it still crashes that would be awesome!

seems to be fixed

The only downside to the patch is that vulcanite rounds are completely disabled. I might just not end up using the Space Exploration magazine types in the next patch since they seem to be causing problems.