Whitworth fluid steel patent is from 1865 extended in 1879 for 5 years. 1880 is widely understood to be the first Purdey made with Whitworth steel barrels - the records exist. However, even though it was expensive, would not be surprised to find someone somewhere tried it out much earlier.
I'll repost the Reilly info on Whitworth Steel barrels just for information:
In
January 1882 Reilly advertised for the first time guns equipped with Whitworth compressed fluid steel barrels (originally an 1865 patent extended in 1879 for 5 years).*xxx
The first extant Reilly with a confirmed Whitworth barrel is SN
24365, a 12 gauge SxS pigeon gun with 31” barrels - top lever, side fences, low hammers, flat file cut rib. It is dated per the chart to
1882.*xxx
(There is a Reilly .500 SxS BPE rifle from 1876 SN
19953, which appears to have steel barrels; however they may be blued Damascus, the gun description being minimal.)
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