Here is an extremely rare Russian 20rd experimental “Drain” (Channel) plum magazine from my collection. This was developed by the Central Research Institute of precision engineering (TsNIITochMash), formerly known as the Ministry of Defense Industry - Research Institute No 61, located in Klimovsk, near Moscow. The institute worked on development, research and testing of small arms and their components, cartridges and different types of gunpowder. Very experienced, highly qualified specialists worked there, and many of them, including managers, were originally from the Tula factory.TsNIITochMash is primarily a design bureau and was tasked with developing all of the "special materials" and components formed from those materials (such as polyamides and other plastics) for the Kalashnikov family, and had worked closely with Izhmash on the development of the AK-74 rifle. They likely created these magazines for certification and possible future use with any and all rifles of this caliber.Limited numbers of these experimental magazines (~50-100) were issued to motorized and airborne divisions taking part in the AKSU field trails held in Kirovabad, circa 1976/77. You can see surviving examples of these field test magazines in a few museums inside Russia, as well as fitted to a surviving example of the prototype "MA" assault rifle. Some likely served in combat with special units inside Afghanistan, just as those early AKSU's did. These magazines were never transferred to Izhmash for further evaluation and serial production.This one, as far as I know, is the only one in the US, and the only other one that I know of resides with a Russian friend/collector of mine in Russia. His is faded as you can see in the photos. Very rare magazine and highly sought after by collectors in Russia and the US.Museum Photos (Prototype) - Shortened 5,45 mm AKSB74U with PBS-4 Silencer:My Russian Friend/Collector Example:My Magazine in Detail:These prototypes were also hand-engraved with a number (for inventory and testing purposes) and usually had no mold numbers. These "hand written" serial numbers usually don't go past 50-100, which indicates the small numbers involved. Once a certain batch completed initial testing and was considered good enough for consideration at a higher level, it was sent to the respective small arms factory it was made for, for further evaluation, and in some cases more pre-production batches may have been made there as well. In some cases, these often do exhibit a maker's mark. In the case of the 20rd magazine, it was never transferred to the Izhmash Design Bureau, thus only a handful of these prototype magazines exist.