You've gotten the maker's name wrong - it's "Clabrough & Johnstone".
"DW Pilkington" most likely ordered the gun, back in the day.
With Damascus bbls, I would WAG that the gun was made between 1893 & 1914.
J. P. Clabrough came to America and bought a hardware store in San Francisco on the heels of the '49 gold rush. Though they sold many brands, their own arms were manufactured in Birmingham, England. They later also opened a retail store in London.
Their hardware store in San Francisco was destroyed in the great earthquake of 1906, but they relocated and continued operations.
They have traded as D.V. Johnstone, then Clabrough and Johnstone and also as J. P. Clabrough.
On occasion their name has been spelled as Clabrough or Claborough.
Their guns are typically well made, medium grade, weapons.
Many are still shooting, occasionally come on the used market, and usually represent good bargains for a quality British shotgun.
Reprints of their catalogs (Clabrough and Golcher) up to the 1920's are available from Cornell Publications.
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