Vintorez only appeared in chapter 58 (and in mangaka's twitter).
An AK goon that has her eyes, escaping outside the panel borders.
You win this time...
VSS was made for Soviet Special Operations during 1980's Afghanistan when the AS Val could not perform designated marksmen duties over distances. However due to the fact it is a short ranged low velocity weapon made to snipe sentries, the bullet is a 259g FMJ meant to penetrate through body armor. However the VSS is a sniper rifle as it is included with a scope and furniture for precision use up to 400 meters to hit a head sized target.
A government building icicle shooter/cleaner. Civil semi-auto fake-silencer version available in Russia as hunting carbine for about 140000₽ ($2200).
The advantage of all subsonic ammunition is they all have less energy to be controlled. The 9x39 goes 920ft/s in velocity while a typical 12 gauge slug goes 1200ft/s. However a Shotgun slug is not rifled or the fact it behaves differently down a smoothbore (it bangs around). Add the fact that the barrel itself is weighted heavily pretty thick, but only 8 inches long which is half as long as an AKM barrel.
Okey now stop thinking for a bit. What you get, is a carbine that is designed so that a bullet of 485ft*lb energy is unable to move the rifle even if it tried. The most ideal for any precision rifle.
It's maximum range is not 400m because it loses it's flight stability, it is 400 meters because it will lose it's lethality any further.