A set of magazines, three for 7.62x39mm Kalashnikov rifles, and one for SVD (Dragunova) rifles, 7.62x54mmR. For the Kalashnikov mags, you can see the three general standards Russia went through with the AK in 7.62x39mm, until moving to the AK-74 in 5.45x39mm.
The first pattern, commonly nicknamed 'slabside' magazines, are ridiculously robust and stamped from 1mm thick steel, which works and is damn near impossible to wear out, but it didn't take all that long to realize that they're needlessly heavy and expensive. Eventually a new pattern was devised, using thinner sheet steel, with stamped into the magazine for reinforcing strength, these were much more practical, and would see by far the most widespread use, to this day, this pattern is the stereotypical "AK-47 magazine", and in many countries who still uses AKs, these magazines remain in common use, some in spite of having moved on from the AK itself, yet still using the same 7.62x39mm cartridge.
A particular issue had been showing itself with these steel magazines however, in that during spring and fall season (and generally any reliably cold and humid environment), it was found that frost and/or condensation could form inside the magazine bodies, and over periods of frost and thaw cycles this could cause surface rust to gradually develop in the magazine, which if left unattended to could lead to the follower to struggle to move smoothly, or in the worst case, at all, which obviously can lead to reliability problems.
Initially aluminum was considered as an alternative, original prototypes were just the same 'ribbed' style, then a 'waffle' pattern style was devised (seen here >>94477
), and put into minor use, but they quickly found them unsatisfactory.
Synthetics would instead be pursued, a material called phenolic resin, sometimes nicknamed Bakelite (which it strictly isn't), the body of the magazine would be made of this material, with embedded steel reinforcements for the locking lug and feed lips.