The inserts are shaped spherically on the top and flat on the inner portion that contacts the scope. Also, the rings are machined with this same spherical shape to match the outside diameter of the inserts.
This allows the inserts to self alighn in the rings and produce a totally non stressed mounting system. There is nothing that is easier on a scope then this system.
How do they hold? Well I have mounted them on 458 Lotts, 50 BMGs and even handguns in 500 S&W and have yet to every have a system slip when these rings and inserts are mounted correctly. This means totally cleaning and drying.
The inserts will grip nearly 200% more securely then any metal ring system simply because the composite inserts have a much higher frictional coefficent then steel or aluminum rings do.
Also, they will simply never mark the scope tube, EVER, if installed correctly and not ever tightened.
If you find a combo that gets this system to slip let me know as I have yet to find it. I do not endorse these to be used on 50 BMGs but I have used them with good results. Still I recommend a tactical style ring, not for scope hold integrity but for ring to base strength with heavy extreme range optical systems.
Yes, the standard Burris Signature rings will fit in the Leupold base. Be sure to apply moly grease to those dovetails but yes they work perfectly well.
The Burris Signature rings have a ring diameter that is much larger then 1", closer to 30mm and the inserts take up the extre area for the 1" scope tube. Order 1" signature rings for your 1" scope. FOr a 30mm scope you would order 30mm rings, same as any ring.
Each insert is clearly marked for its offset amount. They are marked with the following indicators: 0, -5, +5,-10, +10, -20, +20.
You are correct in that these are in Thousandths of an inch and not moa, my mistake. I do not have the direct conversion to MOA but I can assure you that you can easily get enough added MOA to take you to the outter limits of your rifles potential.
Go to http://www.burrisoptics.com/rings.html
and this will explain the system better.