This paper model is a Bulldog 6 (Revolverniy Granatomyot modeli 6), a six-shot 40 mm portable grenade launcher appearing in the open world first-person shooter video game S.T.A.L.K.E.R., the papercraft is created by X.Diem.
The Bulldog six is the only stand-alone grenade launcher featured in the entire S.T.A.L.K.E.R. series and it's a rare weapon in all cases. The weapon is invaluable for short-medium range rapid bombardment and flushing out troop concentrations. Its major drawback is that it has by far the slowest reloading time out of any weapon, especially when expending out all six grenades. Getting caught in a fight with other stalkers and/or mutants while reloading this weapon can get you killed quickly. One will need to practice how to use the weapon effectively at all ranges as its ability to rapidly launch 6 grenades is an invaluable asset. [Source: wikia]
You can download the paper model template here: S.T.A.L.K.E.R. - Bulldog 6 Grenade Launcher Free Paper Model Download