Nice to know .. the guns do at least need 1 ammo in each before they start to use what is available in the inventory.
My mod will only put items into the main inventory. Once I can get access to query the type of guns in the spidertron I can look at populating the ammo slots automatically.
Looks like you can also apply filters to the ammo slots, so that might be something I can use instead of looking at the gun definitions.