It looks like this weapon was the subject of a brutal attack. A factory message on the butt indicates that the shotgun comes from a limited edition batch, notable for its better coating and the terrifying name: "Ripper".In-game description
The Ripper shotgun is part of an optional mission provided by a Duty officer in the Agroprom. The Duty member who gives the mission states that it has a sentimental value, and threw it at a Pseudogiant when he ran out of ammo in order to cover his squad and escape - after throwing it at the beast the Pseudogiant stopped chasing the Duty squad and proceeded to gnaw and bite the shotgun.
The Ripper shotgun can be found atop a hill between both ways to the Garbage. The hill where the shotgun is is guarded by a lone pseudogiant (that never respawns). The shotgun itself is available in a stash in a hole near where the creature is, and only appears when the related quest has been given.
There is no difference compared to a regular SPSA shotgun, aside from the unique name/description and that it cannot be upgraded. Unless the player would like to use this as a shotgun upgrade until they get a real SPSA, it is best to hand it back to the Duty quest giver for a reward.