"It is just an illusion, manufactured in a lab next to the sarcophagus..." The subject matter of this article was cut from the final version of a S.T.A.L.K.E.R. game.
The Jackhammer Mk3A1 is an automatic shotgun that was supposed to appear in S.T.A.L.K.E.R.: Clear Sky, but was never realized even as a basic model. The weapon was a famous prototype (never entering full production in real life) that was also featured the contemporary game Fallout 2. (Much like two other Fallout 2 weapons that did get coded as Easter Eggs in Clear Sky, the Bozar and .223 pistol.)