Don, I will have to pass. Family member saw me researching this and explained I have a Holosun 507k waiting to be opened Christmas day. This is a great deal for someone....
Always used a depth micrometer. I would use silicon carbide sandpaper on a square/glass flat surface, then do figure 8's with equal pressure. I had some 90's that had like .015" clearance - I would take off .010" to .012"..