Perhaps we can help one another. I can trace my ancestry back to a William Mould, gunmaker, from Wiltshire. He moved to Bath (by the 1850's) but as his daughter, Mary Ann, was born in Salisbury, I imagine that he lived there at some time. Brief searches at Trowbridge Ref Librarydo not show him on the 1841 Census, though a William Mould, carpenter,was active in Fisherton Anger (Salisbury). Perhaps that was him. There was another Wiilliam Mould - a "turnkey" at the County Gaol - in Salisbury, on the 1851 Census who was born in Fonthill Gifford (close to Tisbury); furthermore a Sarah Mould, 19 years, was a servant in theChinn household (head was a butcher) in 1851 on Butcher Row. She came from Tisbury.
Have you come across any gunmaker Moulds in your researches, or have any info you think might help?