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Old January 19, 2010, 04:56 PM   #5
Join Date: June 23, 2008
Location: Mill Creek, WA
Posts: 27
I did a crapload of research on this, and based on my findings:

* Crimping degrades accuracy, regardless of whether or not the bullet has a crennalure.

* If there's no crennalure, you definitely do not want to crimp, regardless of whether or not the ammo is going in a semiauto.

* Assuming that your case is properly (neck-)sized, the amount of force required to push the bullet farther back into the case is greater than the force generated by the recoil of the rifle, as felt by those rounds bumping back and forth inside the magazine.

* Are you using bullets that are high enough quality that they are all the same length and have identical dimensions, is all of your brass extremely high quality (identical weights and powder volume) and sized and trimmed to an extremely high tolerance, and are your dies good enough to consistently seat the bullets exactly straight in the case? Because if you answer "no" to one or more of these - and I'm going to call BS if you don't - your bullets are already all loaded at different pressures. So unless you've loaded them to extreme pressure levels (in which case you better be sure that you answered "no" to the above questions, or at least are verifying each and every round you reload) losing a thousandth of an inch or two due to compression is quite unlikely to make any difference, safety-wise.

My suggestion: For semiauto use, work up loads to either max load data *or* until you just barely see signs of high pressure, then (if the latter) back off .2-.3 grains and use that as your load. And don't crimp anything, regardless of crennalures. I bet you'll get better accuracy than if you worked up a higher-pressure load with a crimp.
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