What is this "rust cannon" everyone is talking about? Is this something that is confirmed? or is it just a fan name for it since Ironhide was shot and killed and rusted away. Because I for one think the "rusting away" of Ironhide happened for two reasons. 1.) They needed it too. Optimus has the matrix which they have already established can revive the robots if they want to, so if they wanted to kill of Ironhide for good, they would need to make his body unrevivable. And since he can't be torn into 2 by sentinel like Jazz a la Megatron, the whole "fading away" concept was used. 2.) There is a lot of headshots in the franchise, but few spark-shots. I think Ironhide was hit by Sentinel's second shot directly at his spark which pretty much obliterated it causing Ironhide to rust and fade away. It makes somewhat sense, since their sparks are what keep their parts going.