I don't know because it's never happened.
I don't know if it's because I'm lucky, or because I never use a rifle case, or what but I have the M1's, CDS, and MK AR turrets, the Target Turrets, and the Bushnell Tactical turrets and I have never had a noticeable shift on a turret.
Sometimes in the front seat my elbow may knock one a click or two but I just move right back to zero.
Travis