How does reloading work in the Army?

[Bugabear]

This question goes out to the people in the marines and other armed forces. You know how in video games you shoot off a couple of rounds then reload. You first had about 60 rounds but when you reload you know have 55 rounds. Well that wouldnt work in real life because all of your ammo is in magazines and not lying around. So Im just wondering what happen if say a guy just charges at you and you shoot him down with just a couple of shots. What do you do? Reload and waste a mostly full mag? Or just stick with it and hope you dont get into a long firefight? Or say you use up about half you mag? Three quarters? And the only games that I know of that are magazine based instead of bullet based are Rainbow 6 Vegas 2 and warrock.