Descriptions are from a local appraisal done for my late Uncle by a local collector:

Purdey ~.450 caliber double side-by-side rifle by Purdey. Black powder proofed hammer gun with damascus barrels.
Rifle has been refinished. Excellent condition.
A breech loading .40 bore center fire w/ 30" damascus barrels.
Built in 1868. Side - "Purdey"; top - "J Purdey, 314 1/2
Oxford St, London"