Green’s Dictionary of Slang

1. money.

1796		Sporting Mag. Jan. VII 216/1: The Punters who occasionally make their bankers of all the tables tremble by the weight of their metal are Mr. Boone of the Guards [...] and Mr. Dashwood.
1829		Vidocq Memoirs (trans. W. McGinn) III 78: She’s only a fence for metal, tickers, and frippery.
1837		Reading Mercury 20 May 3/4: We hope they will come to the mark well-fledged, as they will not only have the opportunity of laying out their spare metal, but also a fair chance of losing it.
1895		C. Crowe Aus. Sl. Dict. 49: Metal, heavy metal, men of money.
1900		Sydney Sportsman (Surry Hills, NSW)19 Dec. 1/8: The rush on Mardi for a place [is] attributed to the heavy metal of Mr ‘Plunger’ Bievier, who piled his money on the former colt.
1914		Ade ‘The New Fable of the Uplifter’ in Ade’s Fables 111: The Simp that pushed his Metal into the Box Office wanted Something Doing every minute and many Gals.

2. a pistol, a revolver, a gun.

2000		J.J. Connolly Layer Cake 110: The hounds round here ain’t dressed right if they ain’t carrying metal.
2016		1011 ‘The Truth’ 🎵 No this beef can't settle, that's why I step with the metal.

3. a bullet, ammunition.

2004

T. Dorsey Cadillac Beach 189: On the other side, a man was pacing. [...] Talking to himself: ‘Need to run down the Chinese angle on the shylock’s mazuma before the twist cops a roscoe and squirts metal at the brunos.’.