This just came up on the radar, its inventors, the Iowa National Guard, call it the Ironman
. Very neat piece of equipment, straight from backyard engineering to milspec.
For Traveller purposes, this would be an 12kg backpack, holding 500 rounds of LMG ammo (7mm) together with a feed system for sustained firing. Call it Cr2200 and volume 14 liters, mass 2kg sans ammo load.