At first, I was thinking that maybe it was a tubular mag rifle, like the Remington-Keane but the sights and barrel muzzle device are all wrong. I’m leaning heavily towards prop. The endcap on the forend looks weird. If it is made from real parts, I think that they turned the barrel and gas tube upside down.

Hopefully someone recognizes it or its parts and can shed some more light.

Edit: The barrel and gas block look somewhat like an SVD but upsidedown.