I'd go a step further and just agree that each attack is however many trigger pulls it needs to be, but for the sake of ammo tracking, it is just 1 "bullet" (unless using the rules requiring multiple shots for autos), which I'd think of more as 1 "barrage", which might be 1, 2 or 3 bullets. It doesn't matter because they all have the same mechanical effect, and the actual number is just for color and irrelevant, which I justify by saying that you can also grab that old standby that action heroes use, the "Tardis Pistol", where they fire more bullets than the gun actually holds, so a hero can go into a fight with 15 bullets and come out of it somehow having used 19.
Past this, I myself tend to handwave ammo completely unless something hinges on it. While I agree it can introduce some variety if a PC runs out of ammo or needs to reload or something, overall, I might add that in as a fiat if I felt it necessary, but don't like tracking ammo or for players to scramble for rules and equipment lists and mentally recount or read their erased smudges to try to reconcile how many shots they've fired - it simply isn't worth all that to me and to me sets the wrong tone of miserly preserving and constantly buying and stocking up on ammo, which I still think of more as role playing shopping, not particularly enthralling.
I usually treat reloading the same way in a pinch, though I try to keep it somewhat realistic by requiring a PC to be hiding behind something, spend a shot or something or even forgo an attack in order to reload, if ammo is vital - but most of the time, I just assume PC's are carrying spare and are reloading in the various lulls in action and there's no real need to introduce something as mundane as counting beans in a cinematic firefight.
Now, one thing I have toyed with is the idea of an Ammo Roll, which might be called for either when I feel like it (which I'd try to be halfway reasonable as to when it might be necessary) or when a PC's roll is particularly bad (or maybe even good), signaling essentially "emptying the clip" into an enemy, either in a sudden mass or hail of bullets, or as that last single bullet that leads to "click! click! click!" in the middle of combat, causing the PC to (retroactively) realize he hadn't reloaded lately.
My general idea for ammo is that each "typical" amount of ammo in a gun gets a certain die or dice or even die type, so a gun that holds 12 rounds (just for example), has maybe "rounds/5 or rounds/6 = Ammo Dice" or 2 in this case. So a PC with a gun that holds 12 bullets has an Ammo of 2D6. When an Ammo Roll is called for, every roll of 3 or 4 causes no change and is ignored, a roll of 1 (or 1-2 if you want) temporarily reduces the Ammo by 1D6, but every 6 (or 5-6) raises it (only for the sake of counteracting the low rolls). So if you get a 1 and a 2, Ammo in our example gun drops from 2D6 to 0 - when this happens, it means the gun has run out of bullets (or jammed or broken depending on the situation) and needs to be reloaded before it can be used again. I suppose you could use this to keep track of ammo in a less finicky way; your gun might be reduced from 2D6 to 1D6, making it more likely to run out at a later time, until it is reloaded, with "ammo" being changed from a static or set number, such as 19 in an auto pistol, to say 4D6.
A variation on this is that the dice rolled are summed instead of read individually, with the target number for any gun being Ammo Dice x 3, so a 2D6 Ammo gun needs a roll of 6+ or it runs out, a 3D6 needs 9+, etc; in this way, there is no +1/-1 step ups/downs or subtracting dice - either you roll a 6+ and have ammo, or you don't, and don't. Same works with arrows and I guess with a little extra suspension of disbelief, even shurikens and knives.
Either way, I still much prefer this method to actually tracking ammo, as I'd rather deal with ammo when and if it becomes an issue by virtue of popping up significantly, not MAKE it an issue by counting every shell. One last modification to these Ammo rules is that instead of being completely out, a PC knows he has ONE shot left, allowing for the gritty or dramatic scene where he has to figure out what to do with it, how to maximize its usefulness, before he is left without a firearm, so this doesn't just sneak up on a PC and catch him completely unaware every time. You could even gradiate this, like say in the 1-2/5-6 step rule, your Ammo actually drops to -1, you would be OUT of ammo right then, but if it only fell to 0 you still have one shot left, or with the summing Ammo x 3 roll, your "1 left" range is the target number -1 (6 - 1 = 5 in our example) down to that same number (5) minus the number of dice, with a minimum "totally out" result being essentially rolling all 1's - so on 2D6, with a "plenty" target number of 6+, a roll of 5 to 3 (5 - 2 for 2D6 = 3) is "one left", and a roll of 2 on your 2D6 Ammo roll is "oh crap, I'm out!". So the "safe but only one shot left" range for 1D6 is 2 (1 is an "out" result), 2D6 is 3-5 (2 is "out"), 3D6 is 5-8 (3-4 is "out") and 4D6 is 7-11 (4-6 is "out").
I realize this essentially invalidates all the Schticks and rules dealing with ammo, which is really just fine with me, as I already discounted them when I first saw them, knowing I wouldn't be using them, and have adjusted characters and abilities appropriately since then, so there is no need to get used to a different way of doing things, for me.