Years before die companies made such case headspace gauges, a few were made by custom smiths that did the same thing. Some folks used a standard seating die with a micrometer caliper, like I did.
My first venture was with .308 Win. cases. Took a fired case that I'd trimmed to 1.900" long then pushed it into a standard RCBS seating die until its shoulder stopped against the die's shoulder. Trimmed that short, its mouth was well short of the crimping shoulder in the die's neck. Measured the case head to top of the die (no seating stem installed) and read the caliper. Set the caliper's dial to zero on that fired case. Now the caliper was set to zero at that fired case's shoulder headspace.
Repeated this with a few other fired cases and noted all their case headspace varied a couple thousandths about established zero.
Then I set the full length sizing die in the press and full length sized a fired case. Trimmed it back to 1.900" then put it in the seating die to measure it. The reading was + 3 thousandths from zero. The die had to go down another 5 thousandths to set fired case shoulders back about 2 thousandths. Resetting the die down and resizing that case got the die where I wanted it. The cost of two cases to set up the sizing die was close to nothing.
Cheap, accurate and very usable case headspace gauge. But it's easier and faster with my RCBS Precision Mic's.
One can also drop a GO headspace gauge in the seating die then measure it with the caliper. The dial could be zeroed on it as a reference to compare case headspace to the SAAMI chamber headspace spec.
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Last edited by Bart B.; December 27, 2012 at 03:39 PM.