>>555112
That predates the OICW to the 1970s and (along with tishina) is the reason why Western powers went full retard attaching grenade launchers to rifles. Some retard general saw that and went "THERES A <insert> GAP!"
The caliber is 12.7mm which is a lot more manageable than OICW 20mm. The gun is about a kilo lighter if a Soviet weapon is lighter than a western one, you know you fucked up. It has the option to fire out-sized rifle grenades off of the main 5.45 barrel, but the 12.7mm grenades are exactly what it says on the tin - .50 cal grenades.
It's a good idea, if you're going to go full retard and permanently integrate a grenade launcher it might as well be small so the soldiers arms don't fall off.