Green’s Dictionary of Slang

1. a cannon.

1885		Bulletin (Sydney) 9 May 22/4: ‘But I’ll never regret that I, at the seige of Sebastopol, led the forlorn ’ope after six had been busted, and captured the Agricola [?] at the point of the sword in the mouth of the bunger.’ (Loud cheers; the local for cannon being well received.).
1974		J. McNeil How Does Your Garden Grow Act IV: sweeper: What would you say if I showed you a bottle of after-shave that looked like a fair dinkum hand grenade? [...] mick: Like, Boom!sweeper: Exactly like a real bunger.

2. an outstanding example.

1900

Bulletin (Sydney) 14 Apr. 32/2: Well, one night I wuz sittin’ in the back room givin’ the East what for, an’ all the ladies wus sittin’ round me sayin’, ‘Ho’ow verra naice!’ whenever I’d rip out a bunger of a lie about Jerusalem the ’oly city, an’ Bathsheba.