Canister Rounds

Considered outmoded, Canister Rounds were a way around the limitations of combustion in space, and a direct predecessor to the more widely distributed Gel Rounds. They resemble a traditional powder-grain bullet, but their propellant is a highly compressed gas mixture, meant to be signed by the primer of a bullet.

They were useful in their time, and are still used for non-military tasks, though their shelf-life is their greatest con. Over time, or if sufficiently disturbed, their gaseous propellant can leak out. Sometimes in violent fashion, and not in the way you want it to escape from a firearm. In either case, not useful for a soldier or a hunter who relies on such things as bullets.