It strikes me that limiting ammo in supply Vehicles could be done without having to resort to the whole ammo list. As Zero suggested there are obvious categories such as Tank Main gun, Auto Canon, ATGM, Small arms etc. Limiting the amount could be done based on mass and volume of a truck's carrying capacity and Mass / volume of Ammo. This could then have interpretations similar to the abstractions for digging battle positions where you have Very fast, fast and realistic. So in the mission editor you could have similar things for supply like 2x capacity, 1.5x capacity and Realistic capacity. This could be said to be allowing for a truck to represent 2 trucks or 3 trucks etc.