That automation is partly correct. There are two kinds of belt feed systems. The early ones, used in the Maxim and the Browning, use a claw to pull the cartridge backward out of the cloth belt as the bolt comes to the rear. The fired cartridge is ejected out the bottom or to the side, then the fresh round is lowered down and pushed into the chamber by the closing bolt. The cartridge fires, and the cycle starts over with the feed pawl bringing another cartridge in line to be pulled from the belt.
It is pretty obvious that the system is complex and depends on careful timing, but it is the only way a gun using a cloth belt can work.
But the cloth belt has problems, a major one being that in some applications, like aircraft guns, an empty or partly empty belt flopping around can be troublesome or even disastrous if it gets in the way of something necessary to keeping the airplane in the air, like the propeller. This was gotten around in several ways, including a mechanism that wound the empty belt up on a wheel.
But designers worked on two approaches. One was to make the belt out of steel links instead of cloth or canvas. If these are made so the cartridge itself holds the links together, the belt will come apart as each cartridge is pulled out, and the link that held it is pushed out the side by the incoming belt. An aircraft system will direct the links down a chute and out of the bottom of the aircraft. (They are light enough that they rarely damage anything on the ground - the bullets do more damage when they fall, but war is hell.) That system is called a disintegrating link belt. So even though the gun still pulled the rounds back and down, the cloth belt was done away with.
But steel links can be used without disintegrating and allow the belt to be salvaged and re-used.
Now comes the big development. Instead of pulling the cartridge back out of the belt, lowering it to the line of the barrel, and pushing it into the chamber, let's design the link with an open space at the bottom so the bolt can just push the cartridge out of the belt and directly into the chamber, making feeding a lot simpler and the mechanism less complex. And if this "push through" belt can be made of disintegrating links, so much the better. (The automation shows a push-through system which obviously won't work with cloth belts.)
One of the first guns to use a push-through steel link belt was the German MG. 34, and the feed system allowed a high rate of fire. The later MG. 42 used the same belt, and fired even faster. The German belts, though using steel links, were not disintegrating, the links being connected with wire loops.
Through WWII, the U.S. continued to use the Browning machinegun, with steel link disintegrating belt. But after the war, the Army developed the M60 machinegun, which used a push-through steel link belt that also is disintegrating. Most belt-fed machineguns in use today employ that system, except for old design guns like the .50 Browning gun, which uses disintegrating link belts but on the old pull-out system.
HTH
Jim
