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. Surprisingly not content to just kick things, Kickback also plays with 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.

Movie continuity

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?