A bit late in the day but here is what IGC has on the firm:

Name Gye & Moncrieff
Address1 60 St James's Street
Address2 44 Dover Street
City/Town London
Country United Kingdom
Trade Gun & rifle makers
Dates 1875-1887

Notes

Lionel Gye (b.1841 in London) was the son of Frederick Gye (b.1810). Lionel was an artillery officer before taking over from his father. Frederick and Lionel owned the Royal Italian Opera House and had interests in Covent Garden (which they eventually owned outright) and Drury Lane and, from 1821 to 1840, Frederick owned Vauxhall Gardens. Lynedoch Needham Moncrieff (b.1842 in Scotland and no relation to the Needham gun making family) was the son of Colonel George Moncrieff. Lynedoch was a Flag Lieutenant in the Royal Navy and was recorded in the 1871 census on board the "Narcissus". After he left the partnership he became H M Consul in Suakim, Tokar, Sudan where he died. The 1851 census records Lynedoch as a 9 year old at Sefton Park School in Upton cum Chalvey, Buckinghamshire. The Gye family were recorded in the 1861 census living at Springfield House in Lambeth. Frederick and his wife Elizabeth only had four children but their staff included a cook, two housemaids, a kitchen maid, a butler, footman and coachman. Frederick had an interest in shooting and was a guest of Viscount Dillon at Dytchley Park, Oxfordshire where on 27 November 1878 he was accidentally shot, he died of his wounds a short time later. At the time of his father's death Lionel and his family were living at 3 Collingham Place, Kensington. Gye & Moncrieff were recorded as being in business in 1876 at 60 St James's Street, London, but the partnership may have pre-dated this because on 20 April 1875 Alexander Moncrieff (possibly a cousin b.1830), Lionel Gye and Lynedoch Needham Moncrieff registered patent No. 1435 for a bar to hide the rib of shotguns and rifles. On 8 March 1878 Lionel Gye registered patent No. 950 for an opening cocking trigger plate action which had a box in front of the trigger guard to house a cocking lever. Very few guns were made as Westley Richards threatened a legal claim for patent infringement. On 7 August 1878 Lionel Gye registered patent No. 2123 for a chamber for a necked cartridge. On 5 November 1878 Lionel Gye patented an electric light which he had made and used to illuminate his opera productions.

On 29 November 1879 Lionel Gye patented a cocking mechanism and safety for hammerless guns (patent No. 4902). Although Lionel Gye has not been found in the 1871 census the 1881 census records the family living at 48 Redcliffe Gardens, Kensington. At that time he described himself as a retired artillery officer. The family employed a cook, two nurses, a housemaid, a kitchenmaid, and an indoor servant (rather than a footman or a butler). On 20 October 1881 Lionel Gye registered patent No. 4585 for a side-opening double barrelled action. On 16 March 1882 Lionel Gye registered patent No. 1282 for an improvement to his patent No. 4585 of 1881. On 10 June 1882 Lionel Gye registered patent No. 2746 for a modification to his patent No. 4585 of 1881. Despite a number of patents this firm's early guns were made for them by the trade and were engraved "Constructed for Gye & Moncrieff". Later guns were engraved "Constructed by Gye & Moncrieff". The firm had a good reputation for its rifles. In 1886 the partnership moved to 44 Dover Street but were not recorded after 1887.

The 1891 census records the family living at 40 Sinclair Road, Hammersmith. Lionel described himself as a 50 year old retired artillery officer. The family employed only a cook, housemaid and parlour maid. The 1911 census records Lionel living on his own in, presumably, a convalescent home at 161-163 Cromwell Road, Kensington. He died in September 1923 aged 82.

Other Info
The firm sold shotgun cartridges under their own name.

Tim