I can't think of any ideas about how to make gun fights more interesting in general (besides watching some action movies with extended gunfights and trying to come up with mechanics that emulate what happens in them), but I do have some ideas about ammo tracking.
For starters, you don't have to have explicitly magical guns to avoid tracking bullets. If ammo is plentiful and the characters can reload quickly and without problems, you can forget about tracking ammo. And even if those things aren't exactly true, but those things don't lead to any sort of interesting situations, you can ignore them as just the specific level of abstraction the game is using. Unless you keep meticulous track of the amount of calories players take in and use up in a day, you can probably get away with just asking them to buy a certain unspecified quantity of ammo every month to replenish or bolster their stocks.
If, however, having to reload or running out of ammo in any capacity would in any way be beneficial to the game (not necessarily the players), you can instead roll to ammo. Either as part of the attack roll or its own separate roll, you can roll to see if you're out of ammo, which could either mean you need to reload or you need to think of something to do that doesn't involve bullets. For reloading, you can adjust what number range you want avoid rolling (and maybe the dice rolled itself if using a separate roll) based on the size of the gun clip to differentiate them, possibly including different chances for different firing modes. I'm not sure I'd actually recommend rolling for your total bullets on hand, though it might be Fun if you rolled to run out of bullets and then had to scrounge around your person to find some more ammo.
On a somewhat related note, if you're still tracking inventory by weight, stop that immediately and
use this system instead. Not only is assigning items to slots quicker and easier to use than a weight-based system, you also become keenly aware of where exactly you're keeping everything, rather than having everything fully accessible in some nebulous hammerspace. You could even adjust this system so that some slots easier to reach than others, meaning that when things get rough, you might have to quickly fumble with a thigh pocket to get another reload in.
If you feel like actually keeping track of individual bullets, instead of just clips, I would encourage you to make them somehow scarce (either in general or just for the fight at hand). One idea I saw in another
forum was that there was a zombie outbreak and the PCs only had 13 bullets between them. Or maybe you might have certain special bullets that are armor-piercing or magic or something; you'd keep track of those and abstract the rest. Basically, if you're keeping track of bullets, you should have a good reason for it.