That said, we're not dealing with green "boots"...these are now hardened combat vets who have seen active conflict for over a year (since late 1998). They understand their supply problem, and they are not going to be operating under the impression that unlimited ammunition is available. Trigger discipline will be higher...
...except that the system doesn't allow for it.
Using one ammo die is
trigger discipline. Soldiers are not trained to take a single shot and then wait. They are trained to shoot at the target until it goes down: double-tap - pause - double tap - pause - etc. If you have a ten-second combat round you will
be firing more than one shot.
Now might be a good time to point out that a player using one ammo die is actually using less
ammo than a player firing one "shot" per round in 1E. Firing one shot per combat round in 1E expends 3 rounds of ammunition for each 5-second combat round. A player using one ammo die in this system expends a maximum of 6 rounds of ammunition in one ten-second combat round. So most of the time, you are actually using less
ammunition per unit time in this system.
What people are complaining about, profligate ammo use and a lack of trigger discipline, is actually a complaint about the loss of control over exactly how much ammunition is expended. You are rolling not only to hit but also for how much ammo was consumed achieving that hit. This offends people because standard RPG mechanics have a certain roll to hit, which is a function of character skill, and therefore the amount of ammo consumed per hit is also a function of skill. When you achieve a hit, your character magically knows this to be so and stops firing, so you have efficient use of ammo.
But in the real world, you may hit without knowing you have hit, and fire again. You may mentally commit to a shot that's unnecessary and take the shot even as the target is falling. You may fire at a falling person thinking he is diving for cover. You don't have efficient use of ammunition. You don't commit to firing exactly three shots; you commit to a rate of fire. So in a sense, the ammo dice concept in some ways may more accurately model ammo expenditure.
The idea of firing exactly three shots is game thinking, not real-world thinking: an attempt to balance resource expenditure with goals within a system of precisely delineated probabilities. The complaint about ammo dice, stripped to its core, is a complaint that the system has randomized that expenditure and robbed the player of that control and precision.
This system has a lot going for it. Suppression works very well. It models suppressive fire in a way that supports fire and movement, which other games do not. It is quick and simple. Certainly, it has flaws: mishaps are too common and serious, to choose the most obvious example. But the rate of ammo expenditure really is not one of those flaws.