In a firefight, you need that ammo to get to the gun. This means it's not that easily distributed between an entire section. You're also going to need the correct sort of pouch on your armour/webbing to carry it. My experience is most of the time the majority of the gun ammo is carried by the gunner. The gun is also a lot heavier than a standard rifle.

As the M60 gunner on my team (because I wasn't present when they decided who would carry it), I carried a lot more ammo. Weight was shifted, and others picked up batteries and radios that I might have carried otherwise.

sa46 addresses it a little bit above that there are different loadouts depending on how you're operating. It wasn't uncommon to move from one place to another with 100 pounds, then drop gear and patrol with a far smaller loadout.

Then again, sometimes your vehicle breaks down and you're now "man packable", which means you do need to be ready to carry a lot. This is really one of the sticking points for women in the military. It's nice to imagine that a specific job will always have a vehicle, but it is doctrine to be prepared to step into the role of infantryman.

> The gun is also a lot heavier than a standard rifle.

Good point. This is a big deal because load carried in your hands or, to a lesser degree, on a shoulder strap is more taxing than load carried on a vest.

Yep, the lucky grunts in the weapons squad get to lug around the 7.62 ammo.

The Army doesn't use the M249 as a crew served weapon (unlike the Marines) so the automatic rifleman on each team usually has 600 rounds of 5.56mm linked ammo to carry around.

I'd be curious to see standard ammo load-out by conflict and country.