The DROPs vehicles can pick up the Ammo pallets and then move them forward to the gun line. Once on the gun line they can drop a pallet near a gun postition and the pallet can then pass its ammo to the gun.
It was done this way to simulate resupply in the field. I hope this helps and answers your question.
Problem solved
At the zoom level I was using, I did not see the green circle showing the mount range.
Please notice attached pictures. Some of the ammo types do not show the amount. Is that because there are none, or is it a problem with the name length?