The Burris signature zee rings work awesome and the inserts wont mark up your scope, if you own a Remington you can rotate the inserts 90 degrees and take care of windage problems also.
For entertainment I sighted in a rifle using the Signature rings. It was tedious, but it did work.
For the original poster, there is a +20 & -20, at least there used to be in the after market kit. You can get a lot of adjustment going from .000" to .020". This can give you minus .020" in the front and plus .020" in the rear. Do a little math with a ring center to center of about 4" and discover just how much movement you can get.
If you don't know means equals extremes maybe one of our math boys will come along and make it simple.
