I've found that it's rare to have characters even go through a full magazine in combat (unless they're, say, doing FA with a heavy pistol), and for the most part EP doesn't like to put characters in situations with lots of combat. For instance, even with my group's ventures into the TQZ, none of my players fired more than 100 rounds, and that's including automatic rifles and the like. That said, if players are using expensive or rare ammunition, I track it pretty closely.

I generally assume characters have enough ammo to get them through several fights and they restock every chance they get. The only reasons I would track ammo is if some plot element has reduced their ammo or the characters are cut off from resupplying for long periods. Honestly something like this is better done with something like Fate (which is why I'm excited for the Fate Conversion). Eclipse Phase is fairly specific about how many bullets you fire and when you have to reload. I'd make larger changes so that combat rounds are more abstract on a whole. Don't track individual shots but instead narrate an attack as an exchange of several rounds. Completely ignore the reload action and work it into how you narrate fails or critical fails ("you line him up in your sights and pull the trigger, only to hear the click of your empty magazine"). If the character has been using lots of burst/auto attacks or has been through several extended firefights without resupplying, then warn them on their next failure or critical failure they are on their last magazine and only have a few shots left. I like how Dungeon World does it where one of the "succeed with cost" options is to reduce ammo. You might be able to accomplish something similar. Have a ammo track that you check off anytime they fail or critically fail a ranged attack. Also mark a box when they use burst or full auto unless they get a excellent or critical success. You could probably get away with 10 or so boxes to track ammo. You could make ammo like integrity stress. After every gun fight roll ammo damage (maybe 1d10 base, more for longer fights). Roll additional damage every time you use burst or autofire. Running out of ammo stress causes you to run out of ammo. If the characters are cut off from resupplying you could maybe do it like Call of Cthulhu sanity. Have a Supplies skill that you have to roll after every gunfight or use of major resources. Failures cause the Supplies skill to reduce making it more likely to fail Supply checks in the future. Critical failures mean you ran out of a specific resource. The nice thing about this is you can use it for more than just ammo.

How often players need to reload/get more ammo really depends on how they work. Listening to RPPR's Know Evil game, for instance, Ross' character Bartleby needs to reload like, every couple of actions. But this is because he's using a heavy pistol and FA attacks all the time. Players who use more controlled actions or have a weapon which has a large magazine rarely have to worry about this. I know know I've never really paused to think about my Beam Weapon using PCs because they have like a zillion shots, so I would assume they find a generic power outlet and juice up in between. When players buy specific Seekers or Kinetic Ammo types, I have them keep track of it. They paid for it, they need to track the specific damage, etc. Since most people only have one or two guns, this isn't a huge problem for them. They buy a big brick of 100 rounds and break it up until they ditch the weapons or need more. For NPCs, I just don't bother. If they last long enough to run out of bullets, I would assume they carry a few spare magazines around.