My bet is it is a completely legit Purdey action, very early one. I have pic of Purdey built in 1881 with same lockplate shape, same pin placement, same carved leaf motifs on the 'detonating' and virtually the same shape to detonating. I'd bet the same man engraved motifs. It is an underlever gun, however, and safety shape is different. Note the lettering, style of fine scroll, even the 'arrow'on the tumbler axle are consistent with Purdey's.
Remember this design was in its infancy in early 1880s and various shapes to fences, lockplates et al were in transitional state.
Don't know about the barrels, though.
Quick Edit: I suspect this gun does not have interceptors -- see Greener's p. 175 (ninth edition) and you will see similar pin placement with his illustration.
Here's a scan of Greener, page 175:
And here's an image of a Beesley action with the interceptor:
I believe the gun at issue does have interceptors.
Curl
![[Linked Image from rbsiii.com]](http://www.rbsiii.com/Guns/Purdey_500_top_360.jpg)
