Warne says this is common with a lapping bar but shouldn't happen with a riflescope. The rifle scope tube is supposed to "flex" when you tighten the top screws whereas the lapping bar doesn't give any due to being solid steel.
They were helpful and are sending me another set of rings just to make sure there isn't a problem with the ones I've got.
Not sure how I feel about the rings flexing my Nightforce though....
