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Old December 27, 2012, 12:17 PM   #3
Join Date: March 4, 2005
Location: Ohio
Posts: 13,647
For measuring case head to case shoulder dimensions, these have the best consistency. However, the gauge they include for measuring bullet ogive contact with the throat is not as satisfactory as using an actual bullet of the type I will be loading in the Hornady LNL Overall Length Gage and then using their companion caliper comparator adapter to measure it with my calipers. They have case shoulder inserts for making case shoulder headspace measurement by using the comparator adapter, too. You can adapted it to different calibers and cases by changing the inserts and gage adapter case, which costs a lot less than a whole Precision Mic. The downsides are that the calipers have at least 0.001" less repeatability than the micrometer thimbles in most hands, though both have to be calibrated by measuring a good quality chamber headspace gauge if you want absolute rather than comparative accuracy.

I don't find that 0.002" seating length or headspace difference is a degree of error that is measurable on the target in most shooting platforms. I use the Overall Gauge and bullet comparator to find bullet ogive position on their adapter. I then use the case headspace insert to measure their adapter and samples of my resized cases, then subtract the gauge length from the average resized length, adding the difference (minding the sign) to the bullet ogive reading I use when setting up my seating die. This way, if my shoulder is, say, .003" longer than the gauge adapter, by adding .003" to the bullet ogive distance from the case head of a seated round, I have made the difference between the bullet ogive and case shoulder the same for my case and for the Hornady adapter case. That's the difference that determines how far the bullet will actually be off the lands when the cartridge is fired.
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