Chaingun ammunition is exactly what it sounds like - linked belts of rounds for the Hail Chaingun and Storm Chaingun Turret. It's cheap and widely available, so there's no excuse for running out in the middle of a firefight.
If you have any gameplay tips, hints, or background information relevant to this topic, please post them here. This outfit is available from nearly every Auroran oufitter, in addition to a few others, such as on Viking in the Tichel system. A ship can hold a maximum of 2000 rounds.