Green’s Dictionary of Slang

a firelock or musket, otherwise known as the ‘soldier’s best friend’; thus hug brown bess v., to carry a firelock, to serve as a private soldier.

1747		Advetures of a Kidnapped Orphan 50: [He] had the mortification on that account, to hear the officers frequently say, that he promised fair to make a useful fellow, as he began to handle Brown Bess with tolerable dexterity.
1776		Wkly Miscellany 16 Dec. 243: If you are afraid of the sea, take brown Bess on your shoulders, and march through Germany, as 1 have done, ye dogs.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Brown bess, a soldier’s firelock. To hug brown Bess; to carry a firelock, or serve as a private soldier.
1789		J. O’Keeffe Highland Reel 63: Brown-Bess I’ll knock about.
1811		Lex. Balatronicum.
1819		‘One of the Fancy’ Tom Crib’s Memorial to Congress 4: Till Brown Bess shall soon, like Miss Tabitha Fusty, / For want of a spark to go off with, grow rusty.
1820		W. Combe Doctor Syntax, Consolation (1868) 149/2: Religion Jack did ne’er profess, / Till he had shoulder’d old Brown Bess.
1830		Yorks. Gaz. 3 Apr. 4/4: At the early age of fifteen I began to serve my country with brown Bess on my shoulder, as a common soldier.
1834		T. Hood ‘Tylney Hall’ in Works (1862) III 378: Not that Brown Bess [...] unless you contemplate a campaign on the continent. Take my single gun.
1841		in Bentley’s Misc. 311: [title] ‘Lines to My Double-Barrelled Gun, Brown Bess’.
1843		Bellew Memoirs of a Griffin I 279: ‘The firelock [...] alw’ys goes by the denomy-nation of Brown Bess’.
1849		W.C. Hall ‘Mike Hooter’s Fight with the ‘Bar’’ in Spirit of the Times 10 Nov. (N.Y.) 452: One Sunday morning, I took ‘Brown Betsy,’ my old two shooter, and all the dogs, and off I sot for the cane brake in the hollow.
1851		Bell’s Life in Sydney 26 Apr. 2/5: An actual live Spanish marine [...] with Brown Bess over his shoulder.
1854		G.J. Whyte-Melville General Bounce (1891) 156: The British soldier, with his clothing and accoutrements [...] – not to mention Brown Bess, his mainstay and dependence – nothing punishes him so much as wet.
1858		Bedford Gaz. (PA) 19 Mar. 1/2: I again stopped to reload ‘Brownie,’ and keeping my eye on my former mark, sent another shot after him. It was a good shot with the rifle, and [I] never went from our ranch without my trusty ‘Brownie’ slung over my shoulder.
1862		Aberdeen Jrnl 17 Sept. 8/2: A dozen years ago [...] the Rifle had not supplanted Brown Bess.
1867		W.H. Smyth Sailor’s Word-Bk (1991) 139: Brown Bess. A nickname for the old government regulation bronzed musket.
1877		Chambers’s Journal 720: Such may have been the case in the days of brown bess, but a spinning conical ball from the Martini-Henry will pierce the largest crocodile [F&H].
1894		(con. 1848) J. Astley Fifty Years (2nd edn) I 50: We were only provided with the good old ‘Brown Bess’ which was loaded from the muzzle.
1902		J.H.M. Abbott Tommy Cornstalk 123: It had found ‘Brown Bess’ very useful in the past; it had done much with the muzzle-loading rifle.
1912		Bulletin (Sydney) 12 Sept. 38/4: In the days of Brown Bess, infantry would engage at 60yds. apart, fire one or two volleys, and then the line that was least shaken would charge with the bayonet, and sweep the other away.
1941		(ref. to early 19C) G. Kersh They Die with Their Boots Clean 138: In Wellington’s day [...] we carried the old smooth-bore musket known as Brown bess.