It's a resin cast off a real scope. Came already mounted ESB style for my Snowtrooper, but he also included the other scope as well, so I could swap it into an ANH blaster sometime if I chose to.
Here's my real demilled Sterling. Came to me as pictured for $315 shipped, and yes I'm pretty sure that's a nice deal, even though it had resin T-tracks instead of rubber ones.