Go back to the SAAMI drawing. See the tapered area just behind the neck that starts at .253" and tapers to .3542"? That's the "shoulder". The .330" in between is called the "datum line".
Headspace is the measurement from the bolt face to the location of the datum line on the case shoulder. There are inexpensive measuring fixtures designed to make this measurement accurately, with a dial caliper, for practically every cartridge.
As you can see, the measurement to this line is 1.4666″ maximum. Now look at the chamber drawing... note that the minimum dimension at the datum line is 1.4736"... or a difference of .007". If you measure a fired case with a headspace gauge, you'll have an idea of the headspace measurement in your chamber. Remember that after a cartridge fires, the case expands, in both length and diameter, to the chamber dimension, then shrinks back a small amount... sometimes nearly unmeasurable unless you have the appropriate length .0001" micrometer, and sometimes as much as a few thou.
The idea is that you want your resized case headspace value to be less than the chamber value. What amount is arguable and may depend on the individual shooters needs, knowledge and the intended use of the gun. Until you understand the difference, stick to the SAMMI drawings and the recommendations provided in your reloading manual.
@Creeper - Thank you, that definitely helps me understand what the shoulder is much better now. I'll be ordering the Hornady Lock N Load Headspace Gauge Kit
I see mention of Hornady Lock N Load Overall Length Gauge (straight)
and Hornady Lock N Load Comparator Set Body & 6 Inserts
on Amazon.com when I go to order the Headspace Gauge Set. Are either of these items something I'll also need?
I'm starting to kind of get the hang of my Hornady Camlock Case Trimmer and wanted to go ahead and make a "dummy round" as mentioned in one of the previous posts. I was able to trim my casing to 1.750 , but when I go to seat the bullet it pretty much floats freely in the casing. I could press it all the way inside the casing or shake it and let it fall right out.
Obviously the case mouth is larger than it should be?
Is this the result of me using the sizing die improperly or is this from the chamfer/deburr during case prep on my RCBS Trim Mate Case Prep Center?or both?
The bullets I am using are Hornady Varmint 22 CAL .224" 55gr SP w/ Cannelure
(got 500 of these for free when I bought my press)
So again I'm returning to the question... How do I properly set the sizing die? Or do I have the wrong die?