That sir,is what Mr.Greener called a Grade G Gun,or Self-Acting Ejector. The serpentine fences and scalloped back should make it a G-45 grade,(price was 45 Guineas)a mid grade gun.I would say the gun was made in the early 1890's.
The forearm looks right,stock not so much.
If the action ever needs work,talk with Greener's first!