I'm running a K2 + SE game and Bullet Trails is a recommended mod for SE and suggested for K2.
Today I was looking for a better power mod, I stumbled on this and tired to install it.
Without this mod the game starts smoothly (with Real Fusion Power installed), with this it crashes.

Factorio version: 1.1.50
Error log:

Error loading mods
Failed to load mods:
bullet-trails__/data-updates.lua:14:attempt to index field '?' (a nil value)
stack traceback:
bullet-trails/data-updates.ua: 14: in function'ado_trail_to_ammo
_bullet-trails__/data-updates.lua:23: in main chunk
Mods to be disabled:
- bullet-trails (0.6.1)

Don't know what causes it nor how to fix it, try asking bullet trails' developer.

This seems to be both a Krastorio 2 issue and a Bullet Trails issue.

Krastorio 2 seems to remove all target_effects of the weapons added by RFW. Probably as part of the combat overhaul of K2, but I'm not sure why only for those and not for other types of bullets, maybe Raiguard can provide input.

And then, Bullet Trails doesn't handle weapons with an action_delivery but without any target_effect, and crashes.

K2 + RFW works fine and the bullets work too so I'm gonna assume whatever K2 is doing is intentional.