i like the idea of linking ammo crates to objectives, when the obj is lost. you loose that ammo and the remaining ammo gets distributed over the amount of reinforcements left.
example:
axis team defends a map with 5 obj's and 3 stacks of ammo crates. the mapper can set how much total ammo each team gets, and wich dump has wich percentage of the total.
when they defend they only get ammo from the dump that is linked to the current obj. the ammo from that dump gets distributed to them when they spawn( eg: amount of clips and nades). the amount could be set by the commander, who has to find the best compromise between having enough ammo for the entire round, and giving enough fire power to his men when needed.
when you loose an obj with it's dump, then you loose that amount of ammo aswell. meaning that rapidly loosing the first obj's would mean you would have to completely change tactics.
on top of that it would be nice to have a soldier-level system, where each soldier could set that he wants: few, normal, or alot of ammo.
players with the highest lifetime scores get priority for the "alot" option, but everyone has to right for normal and few(selecting few, will allow those of your team who want/need more ammo to get it, like MG's or assaulters. but the amount each soldier gets will always depend on how much is left in the stack.