No, never happened, even shooting as much as 50 BMG and 460 WM. I learned to hold on tightly from the beginning.
I did post in http://www.thehighroad.org/showthread.php?t=576386 the following:
I am always ready and willing to learn something new. The first time I ever shot a scoped rifle, I was notified of the clearance between the back of the scope and my forehead. I was glad someone spent a minute telling me that I should hold on tightly to avoid getting the notorious 'half-moon' cutout in my skin over my eyebrow! I had a 45-70 with a Redfield 4X TV Screen-shaped scope!
I tried to tell a friend whose .308 rifle we were about to sight in. The scope must have been 40 years old or so (as was the gun, but the gun was a lot nicer than the POS scope).
Anyway, I warned him to hold on tightly to the gun as the recoil is going to send the scope, which had terrible eye relief, back mighty quickly!
Bang, blood all over his face and bleeding profusely! Trip to the ER, NOW!
Next day and five stitches or so later, let's sight this baby in, this time, be CAREFUL! I even fired a shot or two to show him it CAN BE DONE.
Bang! Bandage half off, blood running all over the place, he throws the gun on the bench and is mad as he!! that he did the EXACT same thing two times in a ROW! Quickly, pack everything up, get in the truck and dash to the ER! More stitches!
About two weeks later, we finally got to go again as I recall, and this time, his fresh-wounds which were scabbed over pretty well remained untouched! He pulled a good group with the factory ammo he happened to buy and was finally happy! I told him to stock up on THAT EXACT ammo and nothing else, as the gun really likes that ammo and another ammo you might need to go through the sighting-in process all over again!