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Old 12-29-2012, 08:41   #4
Senior Member
Join Date: Aug 2008
Location: FL
Posts: 2,949
Gary, you are experiencing a common misconception new reloaders have with the term "crimping" and the reloading of straight-wall cases for autoloaders. Crimping generally refers to imparting a very light turn of the case mouth into a cannelure (groove) in the bullet. When dealing with straight-wall autoloading cases (9mm, 40S&W/10mm, 45acp to mention a few), you do not want to crimp the case mouth into the bullet. You only want to remove the flare / bell that you formed on the case mouth so that you could begin to seat the bullet. If you attempt to squeeze the case mouth beyond removing the flare / bell, you will begin to squeeze the bullet and, as stated above, actually reduce the case purchase (grip) on the bullet.

If you want to check your die adjustments using a caliper, measure the thickness of your case wall at the mouth and double it, then add the diameter of the bullet. This should be the outside measurement of the case at the mouth after seating a bullet.

Further, you can check for adequate tension on the bullet by performing a benchtop test. Measure the COL of your finished round, press the nose of the bullet against a hard, firm surface such as your benchtop with adequate pressure, then remeasure the COL. It should not change.
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