If I use 180 rounds, I could most likely get some from someone else in the patrol. However, if I use 180 rounds, something went really, really wrong.
The guys that carry more rounds are Machine Gunners. If you are carrying an M4 / M16, you only take 180. That's the standard combat load.
The biggest consideration is weight. The body armor alone is around thirty to forty pounds. Add radios, rifle, ammo, helmet, food, water, etc and you are going to be hurting if you overburden yourself.
As it is, after patrolling for 12-16 hours and covering 7-10 miles, I'm pretty much ready for bed when I'm done.