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Old January 20, 2013, 06:05 PM   #10
Clark
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Join Date: December 4, 1999
Location: WA, the ever blue state
Posts: 3,159
Quote:
wever
Thanks gentlemen, Clark, your quote "The shoulder should then grow between minus 0.0059 and plus 0.0261". So, if I understand correctly, .021 shoulder "growth" could be somewhat expected?
No, I expect the brass to be pushed .008 to .010" forward, the shoulder to push out, and then the case to stretch .006, so the shoulder will look like it got .014" longer on the first firing... but .021" is possible on the first firing, and ... on the second if the shoulder was pushed back too far in full length re sizing.
The brass takes a one time bad hit, but if the shoulder is only pushed back .001" when sized, the brass can still last a long time.
This has little to do with pressure, other than if the loads are too wimpy, the case will not stretch and the fired case will have the primer sticking out .006"
Some of the pressure signs you describe are ambiguous.
Quote:
ejector pin mark on case head along with significant "smiley face" (and horrible accuracy)
blowing the ejector pin into the bolt head with another min recipe.
ejector mark on case head and stiff bolt.
But stiff bolt lift is not good.

Here is a pic of a 7mmRM case head I fired that the primer fell out. This had .017" of extractor groove growth and the primer fell out.
This is very bad. Don't do that.
If you see any extractor groove growth anywhere around the case with dial calipers, the powder charge is too high.
This is not in any book, just what I do.. but I like to see extractor groove measurements before and after firing. If you are certain that there is growth, the charge needs to be reduced by at least 4% for a useful load.
CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.
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