Hi CBL,
Material for some interesting detective work; unfortunately I have not found a complete answer.

Your gun’s oval has a crest and a motto. The crest is one part of a family’s grant of arms; a motto often but not always forms part of that grant. If both are genuine, their combination should make it possible to identify a family.

To put that task in some perspective, books such as Burke’s Peerage, Landed Gentry, etc., are full of errors and it is generally accepted that more than half the “arms” submitted are bogus / not registered with the proper authorities in England, Scotland or Ireland.

The Motto on your gun is a line taken from the Odes of Horace ‘Secundis dubiisque rectus’ which is translated either ‘Upright both in prosperity and in perils’ or ‘Firm in every fortune’. That motto is used by some individuals in the families of Duncan (Camperdown and Haldane-Duncan), Cleveland and Lippincott.

The Crest, showing a Stags/Harts head cabossed i.e. the head is shown full-faced, without any neck showing, is used by members of several families, among them the Hart, Gernon, Gordon, Thomson, Duff and Calder/Cawdor families. In heraldry antlers represent strength and fortitude. None of my reference books show those names associated with the motto supplied.

My guess is that the Duncan/Camperdown connection could be ruled out as their crests primarily have a naval theme (from the Battle of Camperdown). See their crests here http://www.clan-duncan.co.uk/duncan-crest-badge.html

The usual crest for Cleveland is a ‘A demi old man proper, habited azure’, (the torso of a man dressed in blue) and only one branch of that family uses the motto inscribed on your gun.
Lippincott is a Devonshire name; I cannot associate the crest with them either.

As far as I can see, there is no link between the crest & motto and the A. Holford Gower name on the guncase. That owner could be :
13 OCTOBER 1887, Thursday HOLFORD-GOWER - SHILSON At Christ Church, Plymouth, October 10, by the Rev. W.E. Roo[me?], M.A., Arthur Holford-Gower, Esq., of Leicester Lodge, West Brighton, Sussex, to Adelaide Dinham, only daughter of the late Capt. William Dinham Shelson, of Trevarrick, St. Austell, and granddaughter of the late William Shilson, Esq., of St. Austell and Tremough, Cornwall.

Unless the College of Arms has a Grant of Arms to an individual, containing both the crest and motto on your gun, it is unlikely that the exact owner could be established through heraldry. Best bet is a hope that Holt’s or previous owner have a record.
Regards
K.