for the turrets with the inbuilt chests, those are there deliberately since the ammo is loaded and fired by script, not as an actual ammo, for the capsule flower (for example), this method allows the use of the actual capsules without adding another item to be crafted like is required in the rampant arsenal mods variant.
The howitzers need to be re-written to be based on the vanilla arty turrets (added after original mod was made), I have tried to make the transition but am having some issues on that front. While the low tech solution would be better, at the moment, it serves a purpose, so it will stay.