Courtesy of The AK Guy, this image has been making its way around the internet. It is an experimental 5.45x39mm drum contraption that takes a belt of 5.45x39mm rounds and allows them to work in a standard AK74 receiver without any modification to the actual rifle or RPK74. It does this by using the motion of the charging handle going back and forth to cycle the rounds in the metallic belt, pushing the links out, and somehow feeding the rounds into the rifle to be chambered and fired. The first problem I would assume this would have is that there aren’t any 5.45x39mm belt systems that have been used reliably, but then I started looking into it, and the Soviets did experiment with two 5.45x39mm light machine guns that took belts. These were the PU 2, and PU 21 designs. The PU 2 was based on a modified RPK design, that took some elements from the PK machine gun. The PU 21 was a scaled down version of the PK machine gun and designed to fire the 5.45x39mm cartridge. Both of them could take belts in addition to AK74 magazines, similar to how the M249 SAW was originally envisioned. Needless to say, none of the concepts talked about were actually put to use in any large numbers and didn’t go past the experimental stage.