If that's an AC on the barrel flats--not quite clear in the photo--it's a 1977 gun. Looks like a sidelock, but the V. Bernardelli Roma series guns were pretty convincing sideplated boxlocks. Have never heard the "Royal Merlin" model name, in reference to V. Bernies, either sidelocks or boxlocks. John Boyd, who's a former Bernardelli importer and dealer, might have an answer. If it's a sidelock, minimum value would be somewhere north of $5,000.