I just got a Stoney Point headspace gauge. Unfired Federal Premiums 130gr sbt measures 2.040 to 2.042, and the fired cases measure 2.045. How close is the fired case dimension to the actual chamber headspace value? I'm new to this and would like to know how this compares to "proper values" in the scheme of things. Thanks for your help.

You're not checking headspace, you're checking headspace change.

This is fine just don't confuse the two.

I looks as though things are fine...your cases are growing in length about .003-.005.....That's acceptable for a hunting rifle.....I'd be ok with it.

Sorry, I guess I didn't word my question very well. What I'm curious about is how much difference would be typical between the headspace of a fired case and the chamber's overall headspace? I'm trying to understand the descriptions I've read on the subject, wherin they say the case expands back against the breech face, and then the case "springs" back some amount, thereby releasing it from the chamber surfaces and breech face which in turn permits extraction. Does the tension of the spring loaded extraction plunger in the Rem 700 bolt face keep the shoulder against it's seat both before firing and after, or just after, or not at all? One more question...would it be possible to measure chamber headspace by placing plasti-gauge on the head of a fired case and closing the bolt on it? Thanks for your help.

The amount of spring back depends on the elastisity of the brass. A new case will spring back more than one thats been fired a half dozen times. The load will effect it also., a high pressure loading won`t contract as much as a low pressure load will.
The amount of spring back that is needed to allow easy extraction isn`t much. I`d "quess" .001 /.0015 is probably about normal with a modern high pressure loading.