It could well have been a presentation gift, most likely on retirement. Or the owner might have had it engraved out of nostalgia. There isn't room for "Late" to have been inserted after the rest. N isn't a common initial, so almost certainly if you can find a regimental muster roll for a year when he served, you've got him. As I said, the regimental museum would probably have them, or know where they have been placed. He would probably be a officer, but the unwritten law is that a regimental sergeant-major towered above mere lieutenants, and they were quite well paid. There is an account of a sergeant-major doing great execution in one of the cavalry skirmishes of 1914, with his own pair of Webley .455 automatics.
Here is a document drawn up at a review in Aldershot, a training area in the UK, in 1895. I don't know if it is complete, but it does suggest that NBE was out of the army by that time.
http://shadowsoftime.co.nz/P&M1864.html
Here is some information on muster rolls held in the National Archives at Kew - only on paper I think, but there are probably research firms which do regular business there, and could supply a copy at a price:
http://www.nationalarchives.gov.uk/h...sts-1730-1898/
An officer would certainly be in the Army List if you can find the right year, but a warrant officer such as a sergeant-major, who receives a warrant from the army rather than a commission from the sovereign, probably wouldn't be. Most for that period are listed by rank and date of last promotion, so an individual is hard to find. The first of these is a website on which examples can be seen in a rather confusing online form, and the second is a firm from which you can buy copies on CD.
https://archive.org/details/nlsarmylists
https://genealogysupplies.com/produc...Naval-Records/
Initials and unit aren't enough for
www.forces-war-records.co.uk/ . That was how I traced the man who was given my first edition of Lewis Carrol's "Through the Looking-Glass" in 1875 (cheap because the bookstore didn't recognise the publisher's own morocco binding), and took it to South Africa in 1899 (Only in the British Army!) I believe he is the same officer who ended the First World War as a lieutenant-colonel of garrison artillery, which means heavies. It isn't a gun, but has probably been places and seen things like yours.