Hellow Drew,
It has been some very good posts here.
Page 106-107,
Purdey the Definitive History by Donald Dallas
Quiller Press
Copywrite 2000
ISBN 1 899163 63 8
I was at Puredy and have a signed limited edition, which I just noticed...I'd not looked at that page.

The book I could afford, and only with the greatest will did I not drool all over the shotgun; as perfect as man and machine can make. Teh wood is so great and the polish so deep. To this day I can't tell what impreesed me the most, the engraving, or the wood.

To your question about Purdey saying during the 1880's, Whitworth compressed fluid steel was proportionately stronger than Damascus and consequently make lighter barrles. Boring of rifle barrles was also easier as the material was more even.

Purdey was the first gunmaker to use Whitworth's steel, according to Greener.

It was more expensive than Damascus, Purdey charged 2.10 pounds extra per gun. This was back when a pound was worth $5.00. It was stronger under strain than Damascus, harder, more durable and keeps it's brown better.

Whitworth barrels could be confused with cheaper steels and was always engraved Whitworth Fluid Compressed Steel.

At the turn of the century Whitworth steel was used less and less as ordinary steels was developed and accepted for gun barrels.
In the 1890's Purdey's used Krup steel as better than Whitworth's. How ever by early 1900's Purdey reverted back to Whitworth steel.
This is on page 106