Green’s Dictionary of Slang

1. a .45 calibre pistol.

1878–9		A. Garcia Tough Trip Through Paradise (1977) 234: Mexican José [...] with his forty-five leveled at old Gabriel.
1885		C.A. Siringo Texas Cow Boy (1950) 133: Several bullets from the ‘Kids’ well aimed ‘45’ had pierced his body. [Ibid.] 148: I kept my hand near old Colt’s ‘45’.
1894		D.J. O’Malley ‘The Cowboy Wishes’ in Stock Grower’s Journal 7 Apr. 🌐 With a long rawhide reata / And a big Colt’s forty-five / I’ll be a model puncher / As sure as you’re alive.
1907		W.M. Raine Bucky O’Connor (1910) 39: The bunch borrowed a mighty good .45 of mine I need in my biz.
1909		‘O. Henry’ Roads of Destiny 143: He drew from under his left arm his pearl-handled .45.
1917		A.G. Empey Over the Top 128: He wore at the time a large sombrero [...] and a ‘forty-five’ hanging from his hip.
1921		S.H. Adams Success 233: [He] had adjusted his vision to find it focused upon the barrel of a .45.
1925		Odum & Johnson Negro and His Songs (1964) 197: Stagolee killed a man an’ laid him on de flo’, / What’s dat he kill him wid? Dat same ole fohty-five.
1927		(con. 1918) J.W. Thomason Red Pants 167: A service .45 knocks a man down, anywhere it hits him.
1937		W.M. Raine Cool Customer 53: Bucky broke a .45 and examined it.
1943		E. Pyle Here Is Your War (1945) 238: Lennie jumped out of his jeep, pulled his .45 and yelled at the heavily armed enemy.
1947		W.D. Overholser Buckaroo’s Code (1948) 18: On the receiving end of a .45 slug.
1952		R. Marsten ‘Carrera’s Women’ in Margulies Back Alley Jungle (1963) 67: We each held .45s in our fists.
1962		(con. WWII) J.O. Killens And Then We Heard The Thunder (1964) 84: If I had my forty-five [...] I’d blow your goddamn black brains out!
1964		B. Jackson Get Your Ass in the Water (1974) 54: Stackolee went home and got two smokin’ forty-fives, / he came back and placed ’em between Billy Lion’s eyes. [Ibid.] 79: I got one gun, it’s a forty-five.
1969		H. Rap Brown Die Nigger Die! 28: I roam the world I’m known to wander and this .45 is where I get my thunder.
1976		E. Thompson Caldo Largo (1980) 127: Says he had his forty-five hanging just inside the front door.
1978		S. King Stand (1990) 747: Trash turned his head and looked into the bore of a .45.
1994		J. Wambaugh Finnegan’s Week 337: The .45 slugs blasted open his chest.

2. (US tramp) in pl., beans [? the (.45) pistol-shot like explosion of bean-induced breaking wind].

1930

‘Dean Stiff’ Milk and Honey Route 205: Forty-fives—Monicker for navy beans, givers of energy.