Volley gun
The Ribauldequin was a medieval version of the volley gun. It had its barrels set up in parallel. This early version was first employed during the Hundred Years' War by the army of Edward III of England, in 1339. Later on, the late Swiss army employed it.
M61 Vulcan
The first confirmed Vulcan gun kill occurred on 29 June 1966 when Major Fred Tracy, flying his F-105 Thunderchief with the 421st TFS, fired 200 rounds of 20mm into a MiG-17 that had just fired a 23mm shell through one side of his cockpit and which exited out the other side. When the NVAF MiG flew in front of him after making his pass, Maj. Tracy opened fire on him.