How To Taper Crimp In A Groove

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How To Taper Crimp In A Groove

Postby winny94 » Fri Oct 16, 2020 3:35 pm

Im going to try a CEB Maximus this season. However, Im not understanding how you can taper crimp in a groove w/o ruining the headspace. Can anyone explain this to me?
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Re: How To Taper Crimp In A Groove

Postby Hoot » Fri Oct 16, 2020 9:44 pm

Welcome Aboard Win!

Just because a groove is deeper than a minimum diameter for successful headspace, doesn't mean you have to crimp down that far. The depth of the resultant crimp is adjustable by varying the taper crimp die vertical position. It doesn't take much depth down into the groove to vastly improve the hold that the case has upon the bullet. IE On a smooth sided bullet, I might set my taper crimp die's position to produce a resultant mouth diameter of .476. With a grooved or cannelured bullet, I only screw that die down enough the decrease the mouth to .474.
It's like Brylcreem. "A little dab will do ya". ;)
I can't emphasize enough, the need for an accurate measuring device such as a micrometer in every reloading room, for measuring such small changes. Most calipers are not as good at measuring such small variations repeatedly. A good, albeit used, name brand micrometer, can be had off of Ebay for less than a box of bullets. If you or anyone needs help spotting one, let me know. I worked in the Metrology Lab of an aerospace manufacturer alongside a much longer stint in the Engineering Lab.

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
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Re: How To Taper Crimp In A Groove

Postby winny94 » Fri Oct 16, 2020 10:32 pm

Hoot wrote:Welcome Aboard Win!

Just because a groove is deeper than a minimum diameter for successful headspace, doesn't mean you have to crimp down that far. The depth of the resultant crimp is adjustable by varying the taper crimp die vertical position. It doesn't take much depth down into the groove to vastly improve the hold that the case has upon the bullet. IE On a smooth sided bullet, I might set my taper crimp die's position to produce a resultant mouth diameter of .476. With a grooved or cannelured bullet, I only screw that die down enough the decrease the mouth to .474.
It's like Brylcreem. "A little dab will do ya". ;)
I can't emphasize enough, the need for an accurate measuring device such as a micrometer in every reloading room, for measuring such small changes. Most calipers are not as good at measuring such small variations repeatedly. A good, albeit used, name brand micrometer, can be had off of Ebay for less than a box of bullets. If you or anyone needs help spotting one, let me know. I worked in the Metrology Lab of an aerospace manufacturer alongside a much longer stint in the Engineering Lab.

Hoot

Interesting. So if you were to look down on a loaded round from above, you will see the case mouth not actually in immediate contact with the bullet?
As for measuring devices, I typically only reload precision bottleneck rounds, so I'm used to measuring changes down to the thousandth (part of the reason I'm struggling to grasp this straight walled cartridge - measures and practices are much more crude in comparison).
Best tool I have for this job is a set of mitutoyo calipers, but yea a micrometer would be much better for this application
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Re: How To Taper Crimp In A Groove

Postby s4s4u » Sat Oct 17, 2020 6:57 pm

winny94 wrote:Im going to try a CEB Maximus this season. However, Im not understanding how you can taper crimp in a groove w/o ruining the headspace. Can anyone explain this to me?


Ignore the cannelure, it means nothing when you taper crimp.
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