The MG 34 could use non-disintegrating metallic-link belts. The feeding system was based on the direct push-through of the cartridge out of the link into the gun’s chamber. Accordingly, the link had to be of the half-open type to enable the motion of the bolt through the link. Belts were supplied in a fixed length of 50 rounds, but could be linked up to make longer belts for sustained firing. A 250-round belt was also issued to machine guns installed in fixed emplacements such as bunkers. Ammunition boxes contained 250 rounds in five belts that were linked to make one continuous 100 round belt and one 150 round belt. The other feed options were assault drums that contained a coiled a 50-round belt, or a 75-round "double drum" magazine could be used by replacing the top cover with one made specially for that purpose. A gun configured to use the 75-round magazine could not be returned to belt-feed mode without changing the top cover again.