Using a Case Length Comparator


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uneasy_rider
January 26, 2008, 10:51 PM
I am using a case length comparator that attaches to the lower jaw of my caliper. This measures the length of the brass from the case head to the datum line on the shoulder. I have measured cases (from Winchester factory loads) fired in my M1A and am comparing them to my re-sized Lake City cases.

My resized brass is about 0.005" less than the fired Winchester cases.

Am I sizing correctly?

My resized brass will fit into a Lyman case length guage (the one piece type), but it takes a slight nudge to fully seat in the guage. Is this normal?

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uneasy_rider
January 27, 2008, 09:09 AM
Sunday morning bump

Ol` Joe
January 27, 2008, 09:57 AM
I doubt you are doing anything wrong in resizing as you are.

The opimum resize though wouldn`t move anything below the neck for best accuracy/case life. The geometery of the sized case would match the fired except for neck diameter. You should strive to leave the shoulder at its fireformed position and do minimal body sizeing as well. Redding makes shellholders that come in 0.005" height increments to assist in this but, you can adjust the die height without any special tools.
Start with the die a full turn or maybe a 1-1/2 turn off the shell holder. size a case and measure the shoulder datum, turn the die a 1/8 deeper in the press and size again and check. Do this until the sized case matches the fired one and lock the lock ring in this position....Be sure to use a new fireformed unresized case each time you size while adjusting the die. Useing the same case will give a false reading as the brass isn`t being fully worked each time. The walls of the cases are compressed when sizeing and this pushes the shoulder foreward as the brass flows. A previously sized case will have the walls already compressed some and they won`t move the shoulder the same amount.
If you don`t loosen the ring fom the die body all you need from this point foreward is to rescrew the die in the press and go. The only time you will need to double check the setting is if you change brass. A Remington case may be thicker or thinner then Winchester and size a bit different, requiring an adjustment for example. Hunting ammo too may be easier to chamber sized a touch short, as you are presently doing. Especially in dirty, nasty conditions. If there is any hint of stickyness in chambering, bump the shoulder back a couple thousanths and see if that cures it. Hunting/self defence ammo must chamber smoothly 1st, then be of enough power. Accuracy/case life here is a non-issue.

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