Ok, strictly speaking, those guns/bazoo do not run out of ammo. Strictly speaking, they have unlimited ammo.
BUT actually, they ammo is represented as they status. you can see the status by going to your inventory/bag, then hover your mouse over the weapon. If they gun is new, the status will read Good. If you use it quite a lot, it will say Usable If you keep using it even more, it will say Wearing. If you still insist on using it, it will break.

The status basically represent the ammo of the gun.

Hey, SirMax, you said you can repair the guns/bazoo, where? Is it a new function of v. 3?