Well I have the 410 in my hot little hands. Further very close look:

1) The Barrel is engraved - "Converted by Alex Martin" - I assume this was when it was take from Rook Rifle to 410 Shotgun. No proof marks other than provisional proof. And no marks for the 410 proof.

2) There is an A&T mark.

3) I got the forend off. Ran some thin oil down inside, left it for an hour. Then with a piece of leather gently held the forend in the vice and applied a bit of pressure to the barrel. It popped off. Taking the forend apart - it was gunged and rusty so took it apart and have given it a good clean up. There does seem a lot of tension on the latch spring - reassembling it with the plunger the way it was means it will it not go on. Turning it over it does snap on.

4) General condition is a knocked about - there is small piece of wood missing from the comb and there are several dents. There is a layer of hard greesy wax like gunk all over including on the outside of the barrel. Bore is good. Action is tight. I don't think it has done a lot of work. Just been abandoned in a pile of guns and other junk. Inside an elephant foot along with walking sticks, old cricket bats etc in a Scottish Country House perhaps.

It needs a gentle deep clean - any suggestions please. The oil finish is still there, but it has a gumminess on the surface.

5) The bluing is quite worn. There is and has been light rust, but fortunately little in the way of pitting. A re-blue may be in order. Would these have been rust blued or a Nitre Blue?

6) The stock wood is still proud of the action. The action looks just like the Wilkes above, except the safety is behind the trigger guard. There are the obvious pins and screws to remove from the floor plate and through the hand. Does the trigger guard unscrew as well, and is acting as another fixing for the action.

7) The action is cocked by the top lever.

8) When my permission to acquire a 22 Hornet comes through, will order a 22 Hornet blank barrel. I can get one made with 12mm outside diameter. Should be easy enough to ream out the 410 chamber to 12mm bore. The question is then do I try and ream / drill the rest of the barrel to 12mm, (410 is about 10.5mm) or do I simply then draw file the outside of the blank down to the 410 bore dimensions. Good reasons for either approach.

Thanks again for your thoughts. I am enjoying this little project.