Changing the angle of a shoulder?

Hi, I am trying to do an animation without the animation editor to create recoil for a gun. The script tries to change the desired angle of the character's shoulder but it stays the same. I printed the current angle and it is half of pi. Any help?

tool = script.Parent

tool.Activated:connect(function()
    rsh = tool.Parent.Torso["Right Shoulder"]
    rsh:SetDesiredAngle(math.pi)
end)