If the base wh40k mod has the vanilla turret compatibility option on (because thought that that switch was needed), then vanilla turrets can no longer use vanilla ammo.
This is because the part of the script that copies the ammo_category into ammo_categories is run twice, once in the base wh40k mod, and once in this mod. Don't know which one runs first but the second time it runs, it's copying the nil that was written into ammo_category into ammo_categories.
Not sure exactly what fix would be best, but that's a thing.