Hello,
Look what I found in my Easter Egg hunt:

She is a queen born on 9/3/1891. She has not been molested ever since.
Purdey rifle in 450/400 2&7/8 caliber.
The caliber itself is not well known as apparently only Purdey chambered it.
The loading is here:

I.e 96 grains of BP.
This is a much stiffer loading than the regular 2 3/8 chambering. The normal bullet weight seems to be in the 255 grs range. The bores measure .405". I expect the velocity to be in the 1850fps range, which would be pretty close to the .303 BR ballistics.
The bores are as new, so she has not had much use.
She was built for the Marquis of Caudon (sp.?), whom I have not been able to trace yet.
The case shows labels from London and Scotland.
Purdey's record shows that the Stocker was Dean and she was "put together" by Bilston.
Here are more pictures.

She is built with a snap action which makes the Jones lever snap shut on closing the gun.
It's a lot better than the regular system.

She has side clips, island rebounding locks with safeties, a cheek piece and a steel butt plate.

The sights are classic.

The engraving is magnificent, likely by Lucas.

She weighs 7# 12oz, and balances 3" 5/8 ahead of the breech, just as when it left Audley House.

I need now to do chamber casts in order to get some dies made.
Unfortunately the bullet mold is missing. If you know of one, please let me know.

Best regards,
WC