The rules seem to cover only either firing a single shot all of the 10s+ of your turn, or firing some wishy washy full auto mode (when you choose to use the Ammo Dice).
There's nothing to reflect the standard military training of using the single fire mode which should be more accurate than the suppressive full auto (which is not really used by modern military aside from desperate situations, maybe mag dumps as reaction to contact, etc.). Then again, I can declare that I used a single Ammo Die or two and it turns out I fired 1 or 2 shots and got a small bump to effect of my fire.
Do you guys have any ideas and solutions on how to best reflect single fire? And after that, special fire modes like 3-round bursts on SMGs and rifles and so on?
3 ammo dice is effectively 3-round burst mode. All the weapons restricted to 3-round bursts have ROF=3. Rolling 3 ammo dice can lead to you expending 18 rounds but this is over a 5-10 second time period so it represents multiple 3-round bursts. I would not worry about the number of rounds expended sometimes not being an exact multiple of 3 rounds - you can assume a couple of rounds were fired in single shot mode before the selector switch was flipped to 3-round burst.
Sorry for multiple edits...
Rolling 1 or 2 ammo dice could even be rapid single shots rather than bursts. The system is quite abstract. The rules suggest that rolling no ammo dice at all is a carefully aimed single shot, like a sniper would make.
I think the original idea behind the 3-round burst was that the muzzle would not rise so much as with 4+ automatic bursts, making it more like an aimed single shot with a greater chance of causing at least 1 hit. If you want to house rule that you could allow one ammo symbol to be converted to a success symbol if you only roll 1 ammo dice.