The modern machine gun stems from Leonardo da Vinci’s concept of the 33-barreled organ. He saw there was an issue with the current cannon technology, in that they took forever to reload and often misfired. His design incorporated 33 smaller guns connected in three sets of 11 guns that were on a rotating platform. After one set of small cannons were fired, the platform could be rotated to the next set, and so on and so forth. At any point in time, one set could theoretically be firing, one set could be cooling from having just been fired, and one set could be reloaded by soldiers. This increased the overall rate of firing from the weapon, which is why it is considered the predecessor to the modern machine gun. Other designs by da Vinci included having cannons fire in a triangular spread to increase the hit area for the artillery fire. The 33-barreled organ was called as such because the adjacent barrels of the cannons looked very similar to the pipes of an organ.

Sources:

“33-Barreled Organ.” Leonardo Da Vinci's 33-Barreled Organ Invention, 2008, http://www.da-vinci-inventions.com/33-Barreled-Organ.aspx.

“33-Barrelled Organ.” Museoscienza, 2018, www.museoscienza.org/english/leonardo/invenzioni/organo33.asp.

Image Source : Leonardo da Vinci (https://commons.wikimedia.org/wiki/File:Ribauldequins_-_Leonardo_da_Vinc...), "Ribauldequins - Leonardo da Vinci studies", marked as public domain, more details on Wikimedia Commons: https://commons.wikimedia.org/wiki/Template:PD-old.