By: ELR Researcher

ELR Researcher — Sun, 20 Mar 2016 20:22:54 +0000

There is a good discussion of “Headspace Vs Datum Line” in this Jun ’13 AS forum thread – http://forum.accurateshooter.com/threads/headspace-vs-datum-line.3818442/

One thing that is clear is that the location of the datum for a true wildcat (not just an AI) is pretty much up to the reamer and gauge machinist/shop. Seems very prudent to get your gauge(s) when you get your reamer, i.e., from the same source.

Don’t try to get any insight from the “Headspace (firearms)” wiki. That author seems to think that the headspace for a rimless cartridge is from case base to shoulder-neck junction…NOT.

By: Robert Whitley

Robert Whitley — Mon, 20 Apr 2015 15:36:38 +0000

I never saw a split neck like is shown in the drawing above from excessive headspace. The “neck” splits I have seen from excess headspace were typically partially in the shoulder and traveling up through the neck/shoulder junction up a little into the neck area (but typically not all the way to the mouth of the case). An example: The split I am referring to is one you might see (albeit infrequently) when you fire form cases (like to make 6mm Dasher cases from 6BR brass, etc.) where the chamber you are fire forming the brass in definitely has excess headspace relative to the brass case you are using to fire form.

Editor: Robert, I think you are absolutely right, but this is just an example of the artist who created images for the video not getting things quite right. Like you, we’ve seen the split shoulder issue where the case splits during fire-forming and that migrates up to the neck-shoulder junction and beyond.

Comments on: Headspace 101: What You Need to Know

By: ELR Researcher

By: Robert Whitley