Have your friend buy a quality set of rings for the rifle and eliminate the use of shims.
+1
i install a lot of scope mounts, rings and scopes. With quality products there is no need to shim. All Simmons rings, some Weaver rings and some Leupold rings are now made in China: They are pretty sorry. Had a heck of a time with made in China rings and mounts. Now i refuse to us them at all.