I had the same thing happen to me with my 338 win mag. Check to make shure that the top of the rings aren't bottoming out on the bottom of the rings giving you a fals tightness. The recoil of the rifle is causing the scope to move in the rings. To remedy this you could shim the rings or have the rings cut down, so that when you tighten the ring cap down there is a gap between the top and bottom of the rings. Hope this helps.
Buy some Warne mounts and get rid of your scope mount problems. No shims no more lapping.
I had problems with a 300 win mag 200 gr bullets in a light weight rifle. It actually sheared off the Leupold rings I used. Left it hanging by the front mount. Pretty ugly.
Go with the Warne's and don't look back.
I found that by grinding a little off the rings where they screw together, you end up smashing the tube on the scope. I use a product called stik n seal. It is a clear adhesive with a thick viscosity and a high shear strength. I put a little on the inside of the rings and tighten as usual. Then when it dries you can scrape the excess off that squeezed out with your fingernail or toothpick.
If you ever take the scope out it will just peel off of the scope.
I use it on all my mounts.
It happened to me too on my 300 RUM. NF base and rings and 5.5-22x50 NF scope. It slid at least 1/2", all the way back to the rear bell where it stopped. it was cranked down very well, about 5 inch lbs over recommended torque. It did not slide on my Sako 300 WSM with Optilock rings and plastic inserts.