Which is strange. These projectiles can only be generated by firing an explosive shell using a cannon, and I have zero cannons built.
Found the history. It shows base 1.1.8, RampantArsenal 1.0.2 and RealisticFusionWeaponry as the only and last 3 Mods accessing it.
I will look into Rampart first
Projectiles can be creates by scripts directly, using surface.create_entity{}