The issue of high capacity magazine is far more than weight of additional ammunition and the container that is loads greater than 50 shots. A mg must have a magazine that can support itself, ammo all under the stress of brief periods of full auto fire. many high capacity box magazine are designed to be supported by the ground or shelf attached to a tripod. even a free belt has issues beyond the height of the gun that is if hip or shoulder fired. if the length of the belt is longer then the distance to the ground it must be looped and supported requiring a third hand. while some guns may exist that can hold over 50 rounds and support themselves most of those in game, cough german are not among them.