Green’s Dictionary of Slang

a piece of rope with something heavy fastened to the end, used as a weapon or instrument of punishment.

1830		Marryat King’s Own II 113: He always carried in his pocket a colt (i.e. a foot and a half of rope, knotted at one end, and whipped at the other), for the benefit of the youngsters, to whom he was a most inordinate tyrant.
1835		W. Otter Hist. of My Own Times (1995) 59: Weapons called colts, which is a short rope with a heavy knot at the end.
1836		Marryat Mr Midshipman Easy I 182: ‘And now, youngster,’ said Jack, wresting the colt out of Vigor’s hand, ‘do as I bid you — give him a good colting — if you don’t I’ll thrash you.’.
1846		Sun (N.Y.) 5 Dec. 2/2: [outrageous behavior] was resented by a young fellow, named Jenkins, who dealt a blow on Maxfield’s head with a weapon called a ‘colt,’ that is a leaden ball enclosed in a strip of cloth.
1850		(con. 1843) Melville White-Jacket (1990) 141: Besides the formal administering of the ‘colt’ at the gangway for petty offences, he is liable to the ‘colt’, or rope’s-end, a bit of ratlin-stuff, indiscriminately applied – without stripping the victim – at any time, and in any part of the ship.
1864, 1867, 1870		Hotten Sl. Dict. 106: Colt a murderous weapon, formed by slinging a small shot to the end of a rather stiff piece of rope. It is the original of the mis-named ‘life-preserver’.
1873		Sl. Dict.