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Crimping

29 Jun 2020
@ 04:15 am (GMT)

Paolo Consalvi

We know that the crimping of the ball on the cartridge case makes the cartridge mechanically more stable, especially when we use it in semi-automatic carbines and we want maximum feeding reliability. We also know that the pressure defined as "shot start (initiation) pressure" changes with an estimated increase of about 50 bar (default 250 bar in the QL program for standard rifle jacketed bullets), not much in fact if we consider the "factory crimp" compared to the "roll" type which probably has a bigger increase. Normally applies to cannelure bullets. However, we can also apply a slight crimp to bullets that do not have cannelure by deforming them slightly. I was wondering if the crimping also had an effect on the "run out". Finally, it could be yet another variable to be controlled, but if we don't have a real benefit, why work harder? Do you have experience in this regard that justify this practice in long range shooting? Thank you all.

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09 Jul 2020
@ 02:02 am (GMT)

Paul Leverman

Re: Crimping
Hi Paolo. I use mostly Lee products now, having very bad experiences with rcBS equipment. After the first hundred or so rounds produced, I have stopped measuring each step, and instead focus on the run-out after crimping. I think a conservative estimate would be that about 15% of the finished rounds need to be tweaked by a thou or two, maybe three, to straighten them. In a typical reloading session of twenty rounds, two or three will end up outside my personal parameter of two thou or less. That's pretty good for off the shelf dies. My "bump" tool is simply a drilled hole in the edge of my bench. With practice, you can get the ability to adjust the run-out by one thou.
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