The cannons that come with TFP First Edition Voyager Optimus Prime (either Takara or Hasbro) look great with this mold and fit his hands perfectly, I think.
I ended up playing weapon musical chairs and long story short, PRID Arcee's gun is now Evasion OPs. The beauty of it is that it can be held either way since he can hold both weapon pegs; by the gun handle and used like a rifle or over the hand like a weapon arm extension. I don't know of too many figures that can actually hold it that way, but Evasion OP is one of them and looks pretty decent doing so.