Machine gun
Machine guns are weapons which fire small projectiles at an incredibly high rate. You would think that the Transformers would make something flashy or nuclear, but hey, go with what works.
Fiction
Generation 1
Slugslinger used a machine gun, which was later modified to be controlled by Caliburst. It fired rounds of 1,200 per minute. And knowing Slugslinger, he fired it at that rate whenever he saw something threatening or scary. Crossblades counts 35mm machine guns among his numerous weapons. Surprisingly not content to just kick things, Kickback also plays with a sub-machine gun that fires up to 300 armor-piercing, titanium-coated rounds per minute.
Beast Wars
Tarantulas and Blackarachnia had the legs of their spider modes equipped with machine guns. After his upgrade into a Transmetal, Tarantulas had machine guns installed in his shoulders.
Unicron Trilogy
Megatron gained a second Cyber Key-activated weapon called a "Death Machine Gun." It was capable of firing off several energized shots in rapid succession, thanks to its four barrels, and was responsible for bringing Hot Shot, Red Alert, and Scattorshot to the brink of death in the Battle of Niagara Falls. Revelation However, it would not prove as effective afterward, as Megatron's enemies either learned to evade the shots, or could better endure them.
Live-action Transformers movies
After arriving on Earth, Starscream and Blackout downgraded their plasma cannons for machine guns (the other Decepticons presumably followed course). This loss of advanced weaponry was presumably to better disguise themselves for combat on Earth. Prime Directives issue 4
The Autobots, on the other hand, retained their energy weapons. Only Ratchet was shown using a machine gun. Transformers Really thought that one through, didn't you, Starscream?
As more Transformers made their way to Earth, they also adopted machine guns. Arcee, Sideswipe, and The Twins all had machine guns. During the final battle in Egypt, all the Decepticon protoforms used machine guns, either wrist mounted ones or hand held rifles (one protoform switched to the wrist mounted one after his hand held one was destroyed). Revenge of the Fallen
War for Cybertron
Machine guns such as the X12 Scrapmaker were used even before Transformers came to Earth, alongside their familiar energy weapons, during the Great War on Cybertron. Some Transformers had machine guns mounted on their vehicle modes, usually Scout Class warriors. Transformers: War for Cybertron