Green’s Dictionary of Slang

culty-gun n.

the penis.

1896		Farmer Vocabula Amatoria (1966) 140: Fusil, m. The penis; ‘the culty-gun’.
1980		Maledicta IV:2 (Winter) 192: Sometimes this process is combined with a reference to come-juice and coming – e.g. shooting stick or shooting iron, culty gun, cream-stick, cremorne = cream horn.