mickey,

Photo of the Third Bite (if it has one), any initials on the barrels
and year made would help.

Looks very like the W J Jeffrey's (ie Leonard) built guns but would need
more photos to know for sure.

I have found all of the big calibre English guns are all good, well made solid guns.

Not one of my 500's was made by the name on the action !!!!

Estimate of US20K would be conservative, especially snce that gun looks
in reasonable condition (as much can be seem from the photo and not knowing
bore condition).

Hope this helps.

500 Nitro