From Clogopedia, the Natural Selection 2 Wiki
The Ammo Pack is a Marine Commander purchasable assistance utility used to refill a Marine's weapon reserve clips. It can be accessed from the Assist tab in the Commander Menu and dropped by the Commander anywhere on the map. When a Marine is currently wielding an ammo-based weapon, they can walk over an Ammo Pack to automatically pick it up and receive 5 magazines.
Tactical Summary - Ammunition Packs
- Each pack obtained by the player will refill 5 magazines of their current weapon.
- Special weapons such as Shotguns, Flamethrowers and Grenade Launchers will drop leftover ammo as an Ammo Pack.
- To offset the costs of Ammo Pack drops in the field or in foward positions, it may be better to build an Armory instead to save Team Resources.