I agree with George that it's an Osborne. Osborne was one of Birmingham's DR trade makers. I had it's twin, built for Watson Brothers. Although perhaps not the best of the trade makers, there's nothing wrong with them either.

It has Osborne's version of a screw-grip.

Weight is comparable to rifles of the same caliber from the better quality trade makers. Webley's in this caliber are usually of that weight, and handle very well.

From the photos, this gun is typical of the DRs that Osborne built for the trade. It's been well used. Pity that some prior owner polished and blacked the frame. It's a shooter and nothing more. Judging from the description and photos, and having had one of these, I think the price is fair.