Get a few de-primed once-fired cases and a gage and get to work. Here’s a Forster Datum Dial gage. Works well and works for all standard-architecture bottleneck cartridges, as does the Hornady LNL. Each or either gives a “real” headspace number (although it’s not perfectly congruent, without mathematical manipulation, to the figure from a headspace gage used for chambering; that doesn’t matter though: as long as the gage is zeroed it shows the difference, and that’s what matters). By the way, the old standard “drop-in” style case gages might keep ammo safe, but won’t provide this sort of detail in information.

3 thoughts on “headspace_kit”

  1. I have your books. That is where I learned about the Instant Indicator. It sits in a T7 and stays there.

    I use it all the time because I have noticed that the numbers of a fired case change change.

  2. Note the Author uses a Starrett caliper, which are generally $100 – $500 calipers and have resolution down to +/- 0.0005″. The “cheapo” digital calipers (under $50) are usually at best +/- 0.001″. So, if your actual chamber from shoulder to bolt-face is 1.4650″ and the fired cased is actually 1.4640″ (allowing for 0.001″ shrinkage after the case cools), your caliper might show 1.465″ and you say, “I need to set this back .004, so I am going to shoot for a resized dimension of 1.461 “(when it really should be set at 1.460″) and then you measure the resized case and you get 1.461″, when in reality it’s 1.4620″. So, in reality you might only be getting 0.002″ headspace, although you think you are getting 0.004”.

    When it comes to critical dimensions, it pays to get the most accurate equipment you can afford. While a $200+ Starrett might not be needed, or affordable, there are some other very good ones – I have Mitutoyo calipers. If you have some doubts as to the accuracy and reproducibility of your calipers, you might want to increase the safety factor, especially if you are loading for a semi-auto, and increase the headspace to 0.005 or 0.006.

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