I checked with "The font of all (engineering) knowledge", (Tim!) at work and he offered the following: "you won't get far trying to lap aluminium with a steel bar, the grinding paste sticks to the softer material and laps the harder one"! I assume then that the benchrest guys are using steel mounts?!
The other thing I don't like about many types of rings are the "this will fit X+X+X size dovetails" Really, and how far off the boreline is you scope going to be then? These: http://www.deltainc-usa.com/jdkstuff...ext15apr02.htm or these: http://www.bkltech.com/ are a better idea I reckon.