Green’s Dictionary of Slang

1. vigorously, energetically.

1844		J.C. Neal Peter Ploddy and Other Oddities 111: Ho! ho! tolderol! tolderol! chassez across – swing corners – slambang! pigeon-wing!
1853		N.Y. Clipper 9 July 2/6: [S]lam, bang, the gunners would let go into the body of water throwing it in all directions.
1875		M.D. Landon Eli Perkins 116: Both [...] go sliding slam bang against people.
1891		W. De Vere ‘A Black Hills Sermon’ Tramp Poems 24: He got up a blow-out and shindy, and everything went off slam bang.
1903		G.D. Chase ‘Cape Cod Dialect’ in DN II:v 300: The whole thing fell down stairs rattle ker thrash, slam bang.
1910		B.L. Bowen ‘Word-List From Western New York’ in DN III:vi 448: slam-bang, adv. Recklessly.

2. (US) exactly, precisely, directly.

1837		R.M. Bird Nick of the Woods I 23: Down went the Major, shot right through the hips, slam-bang.
1909		L.W. Payne Jr ‘Word-List From East Alabama’ in DN III:v 371: slam-bang, adv. ‘He ran slam-bang into a hornet’s nest.’.
1912		S. Ford Trying Out Torchy 37: ‘Algy [...] roped him and dragged him through a creek. Yes, Sir, slam bang through four feet of muddy water’.
1948		H. McCoy Kiss Tomorrow Goodbye in Four Novels (1983) 165: You can’t go slambang into this. He’s a big man.
1989		(con. 1960s) M. Kingston Tripmaster Monkey 278: The force of his voice flew slam-bang at the listener.
1994		G. Indiana Rent Boy 49: A whole car full of Jersey teens speeding home from their senior prom, [...] slam bang into a tree.