Low on Ammo, Out of ammo, Jammed/weapon failure Compels
Most if not all hand held ranged weapons use ammunition or energy of some kind that gets depleted with every shot. But this is Fate and we don't really want to spend any real time counting ammo.
So here's a sneaky way around it using aspects and compels:
If a character's ranged weapon has a trouble aspect it can be compelled, the weapon could jam for one round or even run out of ammo (depending on whether the compel roll produces a succeed or succeed with style). Bows don't jam except possibly crossbows and bows built with very complex mechanical parts/technology, however the imagination of the GM can be employed come up on the spot with some issue for the weapon especially if they are built on salvaged parts or are antiques. Weapons should included trouble aspects that are clear and self explanatory to avoid confusion during combat.
The weapon will remain out ammo until 'some ammo' is found at which point the out of ammo compel will be revoked. Another character (such as a squad member) can provide the ammo during a fight but will have to take a roll check to see if he/she has any spare ammo to spare. A weapon can only be compelled to jam or run out of ammo once during a combat situation.