I've mounted NF 12-42NXS in Burris Z rings to adjust MOA requirements. Had absolutely
no problems with the inserts. However, the way in which these rings mount to the picatinny is poor at best. The cross bolts are small and easily stripped. The "purchase" power on the rail is questionable and rings seem flimsy by comparison.
I have replaced Burris Z's with superior rings after having MOA requirements done on rails.
Lots of great rings available and YES they will cost you more than Burris Z's ,but if you're mounting a high end scope ,I wouldn't think I would question investing a few more dollars on rings.
I have TPS,Badger,Leupold,Armalite,Desert Tactical and most recently a new idea in stress free mounting by American Rifle.
ht tp://americanrifle.com/scope_rings/default.asp
I have just aquired a set of these but have yet to mount the scope and range test.
JMHO
Gord