Trained people never go "click" in combat, after few bursts or shot they drop the used clip in a bag reload and merge them later. Real combat has a lot of "dead time" is not as fast or frantic as in the movies... and the casualty rate is really awful.
A "gamist" alternative which can be fun for players without real-life experience is to emulate how it works in the movies. Count their ammo in "clips", each of person can carry 3-6 full clips for their weapons "ready" (like the quick potions in diablo :) ). If they want they can carry more BUT they are NOT ready (stocked in the bag or still in their boxes or whatever) each "box" is about 6 clips and weight around 10-15pounds.
Than something like this:
1) Split you weapons by type for the "In combat behavior":
Single shot: The powerful weapons (or the non combat ones) are single shot, spend an action to reload and prepare the next one (sniper rifles, grenades, rockets).
Side-Arms or small clip semiauto (mostly guns): Usually combat last 3rounds or so... If you are in a prolonged firefight sometimes you will need to reload but usually it will be fast and without a noticeable delay.
Auto: Nobody do sprays because your rifle will start to cook your ammo after 1-2 clips in a row. Usually you go for short burst of 3 or 5 rounds each, set the base attack as a burst and the effective clip size will be in the same range as a gun (6-10 "attacks" or so), handle them in the same way.
Full Auto / Suppressive fire: This action is rarely used and is almost never done by a single person, each member of the firing group talk to each other in a fast sequence of burst to prevent ammo-cooking. Usually you do that ONCE to pin the enemy at the beginning of the firefight to allow your mates to prepare and than stop using it. The alternative is the cover fire. You unload your weapon to pin the enemy while EVERYBODY in your team retreats.
2) Experienced people are more careful with their ammo and have better aim, so it is better to say that a Reload Action is needed only for single-shot weapons, after Full-Auto attack or when you did something wrong like a critical failure or similar.
3) Ammo usage is based on the number of Reload Actions used in combat. If they shot once nothing happens. If they did it more than once, instead, 2 Reload Actions = 1 Clip used. Assign an additional reload action at the end of the combat. (Rember that full auto ALWAYS burn the clip).
This method will allow noob or unprepared people to end up without ammo in a single combat but seriously, if you don't find yourself against a zombie horde or in a post-apocalypse settings there is no reason to also track the boxes of ammo left in your vehicles or "at home".