Looks like its from a voer semi auto
That was a thought that ran through my mind also monarman, not that I have one or am that familiar with the rifle.
I am looking at my 10 shot one in my hand right now and it has the exact same construction but seems like a 5 shot one. I am going mainly on the bottom as it slides forward off just incase you have a jammed round it is just so similarThe mystery continues. The build quality I would have thought, points towards an anshutz or similar