Cartridge-based Headspace Gauge

Attention to detail must be observed in forming the headspace gauge from a cartridge, but basically it is an uncomplicated procedure. Begin with anew or fired case of the chosen cartridge—brand is not critical. Run the case through a body die or fulllength sizing die if fired. Leave the fired primer in place by removing the decapping pin if a full-length die is used. Be sure the primer is seated flush with the primer pocket. If using anew case, seat a used primer in the pocket.

Remove the entire case neck to the forward neck-shoulder datum line juncture. Be sure not to alter case dimensions while holding onto case. This should shorten the case length to 1.557 inches. I The case should be clean and free of damage. Pictured here are both new and used cases of different brands. The fired and unfired cases can be cross referenced. use a medium grit grinding wheel for this and square it to-length at the exact neck-shoulder juncture. Remove any sharp edges from the case mouth.

Strengthening the Case I strengthened the case by using Brownells Steel-Bed to fill it. This material has the properties of steel with an extremely high crush or impact resistance. Just mix an amount to fill the cut off case, avoiding air bubbles, and allow it to set for at least 24 hours before using. Working the Headspace Gauge Ideally a "Go" headspace gauge will fit a newly reamed chamber with some feel of the bolt handle on closure and can be adjusted from there.

Here I shall expound on a test that I routinely use when forming anew chamber while using a Go gauge. I normally cut chambers so the bolt Far In so doing, be sure not to oversize the case by pushing the shoulder back, thereby shortening the datum line measurement. With the case neck removed, remaining case length will be 1.557 inches. Among the methods used to shorten the case, a common grinding wheel can be used. Then chamfer the case mouth inside and out.

557. The entire datum line remains. Above center: The prepped 223 Rem case is ready to be filled with Brownells Steel-Bed which hardens like steel, totally resisting compression. Case is cut squarely on the datum line and filled with Brownells Steel-Bed. closes on a Go gauge with a feeling of some resistance. In so doing, most unfired factory cartridges will chamber freely.

If I have formed the chamber so the bolt closes with little or no resistance, I perform a further test by placing a circular piece of paper, about 0.004", between the bolt face and the case head. The bolt may not even close on this 0.004"shim. That’s fine. I perform this test with anew, unfired case as anew chamber is headspaced, regardless of the Go headspace case finally used. I also perform the test when using a conventional Go headspace gauge.

The Sporting Arms and Ammunition Manufacturer’s Institute (SAAMI.org) is actively involved in firearms industry standards and this information should be understood and followed. There are differing definitions of cartridge headspace, but in this context it is defined as a measurement from the bolt face to some point on the shoulder of a rimless case, commonly termed the datum line. In making my headspace gauge from a cartridge, all these important details were closely observed.

For example, headspace is considered excessive if there is more than 0.005" to 0.007" between the case head of a chambered cartridge with a fully locked bolt. Where headspace exceeds 0.020", case heads can actually separate resulting in a damaged or blown up gun. As a staff writer for Precision Shooting Magazine, I had authored a lengthy research article called "How Case Head Condition Affects Bullet Behavior" which appeared in the December 1997 Annual.

In this work I actually monitored bullet behavior as reloaded case heads would stretch to the point of separation on firing. Making a headspace gauge from a cartridge case is a very easy and practical way of getting the job done safely and effectively. Here we can actually make up a headspace gauge to fit our needs with common tools and materials at hand. We may even learn something in the process. AG Far 004" thick is used as a means of testing headspace.

Top 004" paper shim placed on the bolt face in preparation for testing headspace. If the bolt closed with the Go gauge in this test, I would consider it absolute maximum headspace. I normally prefer a light feel of the Go gauge as final headspace, allowing most brands of cartridges to chamber freely while not using the paper shim. The 223 Remington reamer pictured here is one of Dave Manson’s finish reamers (MansonReamers.com, Dave makes some of the finest reamers on the market.