It is possible you have a Birmingham Moore & Harris gun. Here is some history which I hope may be relevant:
In 1829 Wm Moore opened a stock making business at Court, 4 Whittall Street, Birmingham. This may also have been a purchasing office. In 1837 the stock making business at Court, 4 Whittall Street moved to 35 Loveday Street where it was recorded up to 1845. This seems to have been the start of a long relationship which William Moore had with William Harris who occupied 35 and 36 Loveday Street at various times.
William Harris was born in 1817 in Aston, Birmingham. He may have been related to Alfred Harris who traded as a gun barrel maker in Birmingham (see also Joseph Harris of Lionel Street). In 1838 William Moore and William Harris were recorded as partners in the firm of Moore & Harris, also at 35 Loveday Street, but William Harris also traded from these premises in his own name. In 1840 the partnership was recorded at 36 Loveday Street trading as gun and pistol makers; at least some of the guns sold were marked "London" and were marked Moore & Harris, London, and were proved in London. Harris ceased trading in his own name in 1845.
The partnership probably used William Moore's 78 Edgeware Road, London address too. They appear to have supplied the trade as well as William Moore in London, and they also developed an export trade to the USA. William Harris was recorded in the 1851 census as a master gun maker employing 5 men. He was living at 38 Great Hampton Street, Birmingham, with his wife Emma Lucy (nee Hedder b.1813 in Northampton), and his mother-in-law and a servant. On 1 October 1852 William Moore and William Harris patented a hinged percussion revolver which was produced in limited quantities (patent No. 69). By 1859 in Birmingham, Moore & Harris had expanded into barrel and lock making and in 1861 they moved to the Great Western Gun Works at 91 Constitution Hill. The 1861 census records William Harris and Emma Lucy living at 36 Loveday Street. William described himself as a gun maker.
In 1862 the partnership of William Moore and William Harris exhibited military and sporting guns at the International Exhibition in London. In 1864, perhaps because of temporary financial problems (American Civil War contracts ending?) or because William Moore died (no date is known), the business at the Great Western Gun Works at 91 Constitution Hill was sold at auction; the buyers were a partnership composed of "Moore and Harris" and a Mr Richards. The Moore could have been William Moore or his wife or his son, if he had one. Mr Richards was probably Westley Richards. Other reports say that in 1864 and 1865 Westley Richards joined Moore & Harris in a partnership established to save the manufacturing business of Moore & Harris from closure. However, the new partnership closed within a year and the business was sold to W & C Scott & Son who probably valued the firm's USA export market. Moore & Harris are known to have been trading in 1867 from a showroom at 2 Long Acre, London. When they ceased trading is not known, but it may have been prior to 1870 or even up to 1877.
William Harris was recorded in the 1871 census living with Emma at 126 Buckingham Palace Road. He described himself as manager of a gun factory, this was Moore & Harris at 43 Old Bond Street.
Gun example 1: 30" Damascus barrel, no choke. 3" chambers with excellent bright shiny bores, no pits nor dings. Early Birmingham proofs. Nice tight side lever action. Right hammer is correct replacement. Balance of gun appears to be all original and is in excellent shooting condition. This is a very early cartridge gun. Research reveals that Moore & Harris were in business between 1838 and 1864. They made guns under military contract and also made sporting guns for export to the great western firearms company of Pittsburgh. They also developed a reputation for converting muzzle loading shotguns into breech loaders.
Gun example 2: No 5987-Single bead sight on a solid concave rib marked "MOORE & HARRIS, LONDON. LAMINATED STEEL". Light scroll engraved hammer and lock plates. Lock plates marked "MOORE & HARRIS" with game bird scenes on the lock plates and trigger guard. Nicely figured checkered walnut forearm and straight grip stock with flat buttplate and initial oval. Complete with a leather and double faced embossed shot bag marked "4 / lbs".
Gun example 3: Serial 5080. Gun example 4: Moore & Harris, serial no. 1909, circa 1850-60, the second by joseph spires, London, serial no. 46, circa 1830. 14-bore, with rebrowned twist signed sighted barrels, engraved patent breeches each with platinum plug, signed border, scroll and game scene engraved back-action locks, figured walnut half-stock with chequered grip and fore-end, reblued engraved iron mounts, silver escutcheon, and original brass-mounted ramrod with worm, (minor discolouration to locks), London proof marks and maker's mark 'M&H'.
Mike, does your gun have a visible serial number?
Tim