The US Army has been developing the IRONMAN backpack to increase the immediately available ammunition for crew-served weapons. The entire system enables the automatic weapons carrier to deploy suppressing and superior fire for an extended period compared to current 100 and 200 round belts. In short, it takes a crew-served weapon and turns it into a single soldier deployable system for short missions.
The system is comprised of three major components:
The backpack system – this holds an unbroken belt of standard-issue ammunition (around 500 rounds).
Exterior ammo belt guide – Protects the ammo belt until it is
Weapons adapter – Mounts the belt guide to the weapon system.
The Army suitably gushes over the IRONMAN backpack’s development on their website here.
Source: The Firearm Blog