Recoil animation

I have a question about animating objects in Unity. Is it possible to set the animation property (for example rotation) to something like +0.5, not to specified value like 1.5? I want to make a recoil animation for my gun, so the gun should get higher and higher after every shot (and then go back to the default position), it shouldn’t go to the same position/rotation every time, because it doesn’t look realistic. I don’t know how to do this by script, so I would be happy if there is any option to do this using animation window.
Thanks for replies.

Maybe try just using the += operator to increment by the value you want while shooting back to back etc.