The Cosmic Rust Blaster first appeared in the Dark of the Moon film, in which it was being weilded by Sentinel Prime. Sentinel fired several blasts of cosmic rust at
Ironhide until he disentegrated into unrecognizable remains. Sentinel then turned his aim at Bumblebee, who successfully evaded the blaster's shots. It was later used by Sentinel to shoot at Optimus while in Washington D.C but Optimus managed to evade the shots.
Sentinel Prime kept the blaster throughout the Chicago battle - and it was used once to shoot Sideswipe, but he somehow survived it. The blaster was later discarded by Optimus Prime.
The Cosmic Rust Blaster also appeared in the film's Movie Adaptation, where it was wielded by Sentinel Prime yet again. Sentinel used it to shoot Ironhide, as he did in the film. However, instead of shooting him in the back, Sentinel shot him in the side of the head, which began to dissolve it and head down the rest of his body. A second blast from the weapon destroyed Ironhide. After his death, unlike in the film, Sentinel is about to shoot Bumblebee when Skids takes the full blow of the weapon, which immediately kills him. Mudflap, in great anger, attempts fighting Sentinel, but is killed as well.