All those gauges will only measure case headspace; there's no way one could fit in the chamber. Besides, depending on the load used and the case brass metalurgy properties, how much its body shrinks back from being pressed hard against the bolt face, chamber and shoulder walls will vary a thousandth or more. And their reference is tyically the datum diameter on the bottleneck case shoulder. The RCBS ones are made with a loose thimble that's super-glued in place after closing the gauge on a chamber headspace gauge then aligning its zero mark with the gauge index line. But there's a .001" spread (or more) across all chamber headspace gauges for a given cartridge made on this planet. My RCBS Mic for .308 cases reads -.0006" when closed on my Forster .308 Win. GO gauge.
I've seen adjustable chamber headspace gauges with graduations marked in + and - thousanths from the standard GO guage reference. Actually saw one made for .30-06 chambers. I don't know if any are still available. There may be one or two companies that would make you a set of gauges from GO - .003 to NO GO in .001" increments.
I wouldn't get concerned about your chamber's exact headspace. Just set fired case shoulders back 1 to 2 thousandths then shoot the darned things. There's ample tolerance for head clearance (bolt face to case head when rimless bottlenck case is hard into the chamber shoulder when fired). A couple thousanths spread's not made any difference in my match rifles shooting well under 3/4 MOA at 36,000 inches down range. All the cases have their shoulders at the same place for every shot; hard against the chamber shoulder. I don't care about a couple thousandths spread in how far away the case head is from the bolt face. Especially with the firing pin having .060" plus protrusion from the bolt face.
Well, whadda you know; found this web site but have no idea how good they are: