RG-037 (a.k.a 7.62x28mm) was an experimental Soviet cartridge developed in 1983. Its parent cartridge is the 5.45x39mm. The RG-037 has similar dimensional relation to 5.45x39mm as the .300 Blackout has to .223 Remington. If you apply the .300 Blackout case forming method to the 5.45x39mm cartridge, then you’ll end up with something similar to the 7.62x28mm. The initial prototypes of this cartridge were probably made by cutting the 5.45x39mm case just below the shoulder (28mm) then necking down the cut case to .311 caliber (with some neck turning).
The history of this cartridge begins in 1983 when the Soviet union started “Vintorez” trials to adopt a new integrally suppressed weapon and subsonic ammunition. The designers first experimented with loading 7.62x25mm Tokarev cases with heavier projectiles to make a subsonic round. They shortly understood that this kind of solution didn’t meet the penetration requirements of the trials. They needed a long enough projectile to house a sufficiently large armor-piercing core and at the same time be heavy enough to travel at subsonic speed. The new cartridge also had to be loaded with more powder to propel the large bullet and generate enough pressure to cycle a semi-auto mechanism. So they had to design a new cartridge with greater case capacity than the 7.62x25mm Tokarev had.
This is when the RG-037 was born. It was designed by a man named N.V. Zabelin. The cartridge seemed to satisfy all the requirements and they even started manufacturing it in the Tula Ammunition Plant. However, the minimum penetration requirements for the new weapon/ammunition system were raised even more in 1984, which RG-037 couldn’t meet anymore. That lead to dropping the further development of this cartridge. The successor of RG-037 in the trials was 9x39mm cartridge, which was eventually adopted along with the Vintorez rifle.
I think if loaded with modern powders, this cartridge will perform better and it can be reintroduced at least in the countries which armies use 5.45x39mm caliber rifles. Just imagine an AKS-74U (a.k.a Krinkov) rifle chambered in this RG-037 caliber and suppressed. Although, I would rather go with simply necking up the 5.45x39mm case or factory forming the neck to .311 or .308 caliber. Here is what I mean:
The left round in the above image is what could a .311-5.45x39mm cartridge look like. I used Hornady cartridge images to make this mockup because of my “outstanding” (almost non-existent) CAD designing skills.
An AK-74 rifle (or one of its derivatives) chambered in such caliber could get all the benefits that .300 Blackout gives to the AR-15 platform: conversion requiring only a barrel change, effectively suppressed yet powerful subsonic round, same magazine capacity etc.