First ring worked correctly. Base clamp screw threads on second ring stripped before the ring tightened up on the base. The female threads stripped which indicates that they were out of spec. I drilled and tapped both rings for 8-32 clamp screws. This solved the problem and gives a more secure clamp on the bases. I could do this because I was using them on a Picatinny rail base. The mod will not work on a Weaver base because there is not enough room for the larger clamp screw in the base cross slot.
I have read of at least two other failures like this on various forums.
Don't buy these rings unless you are equipped to repair them or until Burris solves their production problem.
This review was written in the old system and had content requirements that are different than reviews written today.