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Old December 27, 2012, 03:33 PM   #7
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Join Date: July 26, 2011
Location: USA
Posts: 1,619
Devices to measure cartridge head clearance

Problems when trying to measure the Head to Datum of a fired 223/5.56 case. 1. The measurement may become shorter as the case body expands, giving a false reading. 2. The firing pin strike may set the shoulder back .006" 3. An AR15 bolt slamming on the long cartridge may set the shoulder back .001" or more. 4. Shell plates may be a different thickness at each station, resulting in a very different shoulder bump. 5. There may be flex in the press/linkage. 6. You have no idea of the true headspace measurement of your firearms chamber. 7. Using "range brass" that has very different springback after firing. 8. To get a good reading, neck size only for 3 firings. These must me maximum or near maximum loadings to fully expand the brass to the chamber. 9. You (no one on this board) can't follow instruction, read a micrometer or vernier caliper. Sorry had to put in #9
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