A Russian gun enthusiast has developed a Predator-style ammunition feeder backpack that holds 7.62x54mmR cartridges for the PK Machine gun. If my understanding of the Google-translation of the Russia text is correct, the backpack, feeding mechanism, ammo box and 450 rounds of 7.62x54mm weigh a total of 33.2 lbs (15.1 kg). The backpack has been designed to give the operator maximum mobility. The gun can be fired offhand or prone and the feeding mechanism reaches far enough for the machine gun’s flash hider to rest on the ground.
Source: The Firearm Blog