It's just that much harder to use your shotgun if it takes minutes to load it... Hard to time that artillery. Would be better if there was some information when the unit was fully loaded, ready to fire (as long as you don't turn them). I might even like it if artillery required another confirming click after the first order to shoot up some enemy unit. That way, you could hold fire until the critical moment. Imagine it like this:
General (already shouted hoarse): "hold... hold... Hold!... HOLD!... HOLD!!!... FFIIRRE!!!!"