So, according to the Clearing house, I should have ~350 rounds for my Assault Rifle. But when in a mission, I only have 120. Another bug. When using the pistol, I have 12 tranqualizer darts. When I switch back to another ammo type, and then back to tranqualizer, I only have 2 darts! There's something wacky going on.

I'm not entirely sure if it's a bug or a not very visible feature. I kept buying enough pistol ammo until I had ~250, but would never be above 150 when in a mission - I assumed it had something to do with carry limits (though ammunition size stats in weapons only means the size of your clip, doesn't it?)

 

Didn't get the switch error, though...

So, according to the Clearing house, I should have ~350 rounds for my Assault Rifle. But when in a mission, I only have 120. Another bug. When using the pistol, I have 12 tranqualizer darts. When I switch back to another ammo type, and then back to tranqualizer, I only have 2 darts! There's something wacky going on.

 

You can only carry a small portion of your ammo on a mission. Armor upgrades like Ammo Pouch allow to carry more.

You get a set minimum (for example, w/o upgrades, 100/50 pistol normal/tranq bullets), plus whatever is in your gun from a previous mission.

Okay, got it. The tranq error is just a display error as I've figured it out.