Phail,
Barrels marked on the underside,"Roses Patent"are usually barrels made under British patent #13299 of 24 October 1850,which is described as; "a new method of making twist barrels by machinery"This likely the basis for the U.S.patent refered to by Pete.
Rose was in business in both Halesowen [In the so called black country/Victorian Industrial Midlands]and Birmingham from 1841 to circa 1900.Rose,s also held other patents for forming barrels from, mild steel sheet,wrought iron and cast steel.
Records for the era that this gun was made do not show a gunmaker named W.Wellington! Could this be an example of the spurious guns that so enraged William Wellington Greener? Or is it perhaps just another example of a Hardware store selling Birmingham guns, engraved with their name? I look forward to other opinions.