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In the Transformers films, Autobots have been shown to use ammunition for their weapons. In the fourth film, one of the Autobots claimed that he ran out of ammo during the battle with Galvatron and his army of transformers created by humans.
So where exactly do the Transformers get the ammo to reload their weapons? I don't think the humans make the ammo because that wouldn't explain where Decepticons who live on Earth get theirs - since the military would never work for them (the 3rd film showed that some people worked for the Decepticons, but I don't know if they had the resources).