Unfortunately I've come across a few of those Burris bases that were undersize in width.
I've never put a caliper to them, but have never had any that a ring won't clamp to, and never had a ring come loose from one. I usually use them in conjunction with the Burris XTR rings and have been completely satisfied. On the XWR above, used the XTB bases with the Super Sniper rings, and so far, they seem perfectly fine.
John
