Never in the cartoon, but it was seen in the comics but never wielded. It was more of a flying space gun, much like Shockwave. Although Galvatron also had the ability to mass-shrink himself in gun mode if he wished. It was in the shrunken gun mode that he would ride in Cyclonus' cockpit (which makes way more sense than TFTM which showed Galvatron piloting Cyclonus in robot mode! ). So yeah, Galvatron's gun mode was seen either unshrunken like Shockwave or shrunken like Megatron. But it was never held; Galvatron was able to fly in gun mode, again, just like Shockwave.