It's not ring inserts, they're replacement ring halves. That portion isnt affecting any zero shift - if they have been installed correctly with the bottom portion torqued before the top portion.
The Larue lever mounts should return to zero when coming on and off as long as you push the scope/mount forward each time and you are tightening the levers nice and tight. If the levers aren't tight enough, the mount can shift front to back a bit until the recoil lug stops it. This will lead to a little bit of zero shift, how much will depend on how straight your rail is. If your rail is perfectly straight, you're probably dealing with under .1moa of shift. If the rail isn't perfectly straight, you may see as much as 4MOA of shift. This would usually show up during a course of fire if the mount is shifting under recoil.
My test for regular rifles with QD mounts is to stand the rifle on the butt stock and put all my weight down on the optic. If the mount will shift, I tighten the QD system. (Test is done after mounting with the mount pushed forward in the slot.) With a .50, you may need a tougher test.