I had some low fired clay bullets laying around, so I wondered what their density was compared to the non burned clay. Here are the results that I want to share with you.
The air dried natural clay that I use has a density of about 2.1 g/cm³. When fired in the wood stove it has an average density of a little over 1.83 g/cm³. When (fired and) fully saturated with water, it has a density just a little under 2.1 g/cm³.

The graph below shows how fast the 5 test-bullets changed their density. The experiment was done at room temperature. I think the bullets will loose the water way faster out in the sun/wind.

So....soak your glandes in water for an hour before heading out to battle?

A serious question though, I wonder if the durability is the same for both.  If you have a dry glande and one that is fully saturated, then sling them into a (solid) wall or other target, I wonder which breaks first.

Good thought.  But if the strength is equal in both, I would assume the wet glande would be more likely to break because of higher mass creating a higher force during the impact (assuming equal mass before the water saturation, and projectiles moving at the same speed).  But I suppose that still wouldn't indicate a strength difference because the force is no longer the same.

It would be cool to see some testing with a hydraulic press like they do in videos testing the failure point of different things.

It just makes me smile reading the hypotheses here...

I reckon this is awesome! I think soaking when holding out in a siege would make sense! Extra ouch factor...