RCBS Precision Micrometer Question

[Vdot]

This question has two parts to help me understand how headspace is measured, and for anyone who use the RCBS precision mic for 6.5 creedmoor.

I like the idea of the precision mic (pm) to measure headspace. The zero line corresponds to the minimal hs value 1.541” with each line 0.001” . The range is 1.541-1.551(max)”

When a case is resized, the die squashes the shoulder back towards the base.

When a case is “bumped” back, we are actually heading towards the minimum value?

Why bother to measure headspace at all? (I know the responses will drag me into the weeds again). Does it matter what the reading is for a given case as long as it chambers and the bolt closes?

i will stop here and hope there are responses before the heart of the reloading issue is presented.

 

[Straightshooter1]

I use this RCBS mic solely to see how much bump I'm getting after sizing. I'll measure a case before I size with it and measure that case again after I size it. I find this mic very fast to use during my sizing process just to be sure I'm getting the amount of bump I'm after. I never use it to measure the actual length of my headspace as I use my calipers and a comparator for that when think I need to know, like when mounting a new barrel. After fire forming, the consistent amount of bump I put on my resized cases is what's important to me.

 

[Vdot]

I have once fired cases that I minimally resized to 1.545", no matter what they measured before resizing above or below this value, they resized to this. They chambereed and the bolt closed, but not empty chamber easy. I seated bullets and went to the range, but more than half were hard to close the bolt. I was disappointed, but now I have fire formed brass.......

I happened to have a batch of rounds from a couple years ago with me...they chambered and the bolt closed in stark contrast-easy and smooth. I brought those home to annalyze their dimensions as follows, with the OP the basis for this post.

The fired cases were back to 1.545" HS. The unfired ammo, using my hornady comparator measured -0.005 or some times that much below the "minimum" (1.541"), 1.536".

If one over resizes you are acually moving towards the minimal headspace numerical value range?
so minimal value actually means a greater headspace for the bullet in the chamber.