I have several NF's -- NXS and ATACR. Bought most of them used and still have never needed warrant work. Whenever I have thought one of mine or someone else's NF was starting to not hold proper POA it has turned out to be a problem with the mount or rings.
I use only Burris Signature rings but they will shoot loose once or twice after you mount them. Keep checking them -- it takes only a second.
I use only Burris Signature rings but they will shoot loose once or twice after you mount them. Keep checking them -- it takes only a second.