This amazing animation of a case unfolding in a complex firearm was created by 3D Artist Akeboshi, known for his hobbyist mecha and robot artwork. Based on the look and the artist's previous mentions, it appears they used 3ds Max for both modeling and animation.
Check out more of their fantastic robot designs and fan art below, created using Substance 3D Painter and Marmoset Toolbag:
If you want to see more realistic robotic 3D art, have a look at Rassoul Edji's progress on the creation of Hyperion, the mecha character from his CG short film: