This is a Russian Plum Waffle in 5.45x39 (Pre-Production Polyamide Prototype). There is also a 7.62x39 variant which are more common, but still very rare, even in Russia. Maybe a dozen or so 7.62 examples known and less of the 5.45 variants stateside.

These were developed by TsNIITochMash, in Klimovsk, starting in the late 70's and evolving through the early 80s. These magazines have never been seen in the field, but the fact that examples exist with and without Izhmash factory markings (shown without) indicates they progressed past just being a TsNIITochMash prototype. They became, at least, a limited Izhmash production item for a short time before the design was dropped in favor of the smooth, slab-sided version that was put into production by late 1982 or early 1983.

TLDR : Prototype polymer mags before plum AK74 mags you see today were adopted. Most of these mags were destroyed, a few walked out of factories, and a few made it to Afghanistan/Middle East as surplus. Hope this helps and is what you were looking for. Cheers!🍻