This is a possible maker of your gun, from IGC, but I am dubious about what you have without further info:
William Powley Hewson / Heevson / Hewyngson / Hewgynson
Other Names George Hewson
Address1 91 North Street
Address2 91 North Street and 26 North Street
Address3 Cowick Street
Address4 127 Forest Hill
Address5
Address6
Address7
City/Town Exeter
County Devonshire
State/Region/Province
Country United Kingdom
Trade Gunmaker
Other Address
Dates 1820-1885?
Notes
William Powley Hewson was born in about 1779, the son of Thomas Hewson, gun stock maker, of 43 Shoe Lane, London. He was a pupil at Christ's Hospital and was apprenticed to Emanuel Mansfield in 1793.
He appears to have worked for Thomas Hewson of 133 Fetter Lane and 36 Piccadilly, because when Thomas emigrated to South Africa in 1820 W P Hewson and his sons George and Thomas, moved down to Exeter and he opened as a "Gunmaker from London" at 91 North Street. He was recorded there from 1823 to 1830, but he was also recorded at 26 North Street in 1827, these were aditional premises which were retained post 1827.
George was apprenticed to his father in 1821 as was Thomas in 1828.
In 1841 George opened his own business in East Reach, Taunton. What happened to Thomas, who had also been a pupil at Christ's Hospital in London prior to the family's move to Exeter, is not known.
In 1843 it appears that W P Hewson retired or died and George closed his business in Taunton to take over in Exeter. He sold the 26 North Street shop to James Osborn and moved the 91 North Street business to Cowick Street where he was recorded from 1843 to 1850. Between 1851 and 1854 the business was located at 127 Forest Hill where he remained until he appears to closed in about 1885.
The Osborns (Charles James Osborn) closed in 1870.
Tim