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Rifles, Reloading, Optics, Equipment
Gunsmithing
How to accurately measure (not validate) headspace?
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<blockquote data-quote="RD57" data-source="post: 1851283" data-attributes="member: 103010"><p>Old timer way to do it, but it still works. Take a fired/unsized piece of brass and measure it from top of neck to bottom of case centered on primer. If the primer is still in the case make sure it is below flush for the measurement. Once the initial measurement is completed, partially unseat the primer with a universal de-priming die by about .004" so you can slip it out of the shell holder. Re-chamber that piece of brass and extract it. The bolt will seat the primer as far as it can with the shoulder of the case against the shoulder of the chamber. Measure the case again at the same points as before and subtract the first measurement from the last. The value you received is the excess headspace with that case. Measure the same case with the RCBS Prec Mic and add the value you got and will have the exact headspace reference from the Precision Mic. Most cases springback at the shoulder after firing by about .002", my freshly annealed cases spring back .001 - .0015". You can actually do this even with new brass. Measure as before with un-primed brass and then partially priming with a used/fired primer. Using a fired piece of brass gives you a better understanding of how much spring back your case's shoulder moved. Most of my resizing FL dies are set up to leave/maintain the shoulder at the expanded fired length as they are easy to chamber.</p></blockquote><p></p>
[QUOTE="RD57, post: 1851283, member: 103010"] Old timer way to do it, but it still works. Take a fired/unsized piece of brass and measure it from top of neck to bottom of case centered on primer. If the primer is still in the case make sure it is below flush for the measurement. Once the initial measurement is completed, partially unseat the primer with a universal de-priming die by about .004" so you can slip it out of the shell holder. Re-chamber that piece of brass and extract it. The bolt will seat the primer as far as it can with the shoulder of the case against the shoulder of the chamber. Measure the case again at the same points as before and subtract the first measurement from the last. The value you received is the excess headspace with that case. Measure the same case with the RCBS Prec Mic and add the value you got and will have the exact headspace reference from the Precision Mic. Most cases springback at the shoulder after firing by about .002", my freshly annealed cases spring back .001 - .0015". You can actually do this even with new brass. Measure as before with un-primed brass and then partially priming with a used/fired primer. Using a fired piece of brass gives you a better understanding of how much spring back your case's shoulder moved. Most of my resizing FL dies are set up to leave/maintain the shoulder at the expanded fired length as they are easy to chamber. [/QUOTE]
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How to accurately measure (not validate) headspace?
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