Other than him though, nothing's really clicking. Like, unless small ones like what BW Optimus Primal count, or the countless "shoulder mounted" cannons that had quite a present abundance in just about everything. Uhh... what series or era are we talking about here, and is there anything else that could narrow it?
G1/Animated/WFC/Prime Starscream, Skywarp, Thundercracker, Ramjet, Dirge, Thrust, Sunstorm, Slipstream, Classics/G1 Acid Storm, Animated Swindle, and DoTM Shockwave.
Uh... specific continuity you're referring to? It would help us narrow it down, as TrueNomadSkies just said.
The number of Transformers characters who have wielded an arm cannon at some point in some manner can be technically referred to as "a shitload".
Hoist and Trailbreaker had guns for hands if I remember correctly???? And Ironhide had the occasional liquid nitrogen hand... ROTF Ironhide had duel arm cannons, and Bumblebee had the transforming arm cannon.
Sorry, I posted this then my attention was never brought back to this. But I am thinking G1 maybe... I know of the seekers and shockwave...then again it might be nothing. Anyone with an arm canon much like Megatron.