I recently wrote about the ASh-12, the new 12.7x55mm assault rifle developed at TsKIB SOO (KBP). Its older brother, or maybe third-cousin-twice-remove would be more accurate, is the KBP VKS Sniper Rifle.
The KBP VKS is technically chambered for the same 12.7x55mm cartridge cases as the ASh-12, but loaded rounds are considerably different. The Ash-12 is 12.7x55mm cartridges are loaded with (relatively) light bullets, much like the .50 Beowulf and the ancient .50-70 Government. The VKS is loaded with very long and very heavy bullets, so much longer that I doubt they would function in an ASh-12. The bullets weigh up to 1170 grain!
The VHS is designed to be a suppressed sniper rifle and would normally be used with a suppressor. To achieve maximum noise reduction in the vicinity of the target, a bullet fired must be travelling subsonically. Kinetic energy is a function of velocity and mass. The only way to increase the kinetic energy of a bullet is to either increase its velocity or its mass. If a round’s velocity can’t be higher than 1126 feet/second (speed of sound), then to increase its energy you must increase its mass. This is why the 12.7x55mm is loaded with such heavy bullets.
According to guns.ru, the rifle weighs 14 lbs (unloaded, but including scope and suppressor) and the magazine holds five rounds. Despite its semi-automatic appearance, it is actually a straight-pull bolt action.
[ Many thanks to Lionel for the photos. ]