Steve,
I don't think I would set it up for a crush fit for rimfire cartridges.On the other hand 1mm below seems excesive. Are you sure it is not .1 or .01mm? 1mm would be almost 40 thousanths of an inch, the difference between go and no go headspace gages is usually 4 to 6 thousanths, depending on the length of the cartridge( 30-06 is .006").
Mike