Ammunition

Ammunition (Ammo for short) is a game element used in surviv.io that is necessary to fire guns. They look like small colorful blocks scattered around. Each gun requires one of seven different types of ammo in order to fire. The color of the gun matches up with the color of ammo it requires.

Casings & Shells
Each Ammunition has its own casing or shell (Shotguns and Flare Guns). Something that is dispensed as a result of a bullet being fired ejecting the leftover casing out of the ejection port. You can see them flying out of the side of your gun while firing.

As you could see some casings are for multiple ammunition types such as 9mm, .50 AE and .45 ACP sharing the same casing. .308 Subsonic does have a casing confirmed in a sprite sheet but has yet to appear on the Developer Kit.

Disclaimer: 12 Gauge sharing the same shell (correct term for shotgun casings) with the Flare is not yet confirmed though from user experience I am sure that it has the same casing.

Trivia

 * The 9mm ammo is the most common, while the .308 subsonic is the most rare
 * Rarity of ammunition generally goes in this order, from most to least common: 9mm, 12 gauge, 7.62mm & 5.56mm (tie), .50AE, .45 ACP, Flare, .308 Subsonic.
 * While certain types of ammo only spawn in limited amounts with their gun of choice, Green Ammo Crates can spawn any type of ammo when broken.