This is a STALKER Shadow of Chernobyl Total Conversion mod. The goal is to create a world as rich as the lore of Warhammer 40,000, complete with original story line, authentic weapons, and remaking of the general gameplay, although the engine will remain intact... because, admit it, x-ray is just an awesome game engine.
Here's that proof that I promised! This is an older model Bolter, often used by the Adeptus Soritatus. I capture the image by way of a render this time, as per the suggestion of Jamie1992. He's cool, in case you didn't know. :P