This may not be for everybody but I recently bought a set of Pin Gauges that go from 7.51mm to 8.00mm in 0.01mm increments. This set is useful for the 30 cal range of measurements. The 0.01mm equates to 0.0004 inches or 0.4 thousands of an inch so a bit smaller than your normal set of micrometers.
What I am using the set for are a couple of things.
1 You can use them in the muzzle end of your barrel to measure how much erosion is occurring and if you are going to re-crown just how much barrel length needs to be taken off.
You do this by just inserting a pin gauge into the barrel and seeing how far it will move into the barrel. Ideally it would be the same diameter bore from one end to another but over time the muzzel end gets a bit larger.
2. It is a really good way to measure the inside dimensions of the neck of you Brass.
By taking the measurements of the neck after the case has been fired, after the case has been sized and perhaps after you pull a bullet. From that you will learn just how much you are working the brass and more importantly how much neck tension you have.
3 You could also turn the pins into expanding mandrels to be used after sizing your brass perhaps a thou or more than you want then using the pin to finely tune the neck to the correct dimension.