6mm ARC Brass Forming

Helidriver

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Dec 6, 2009
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Surprise, AZ
Is it possible to take a 6.5 Grendel case and neck it down to 6mm ARC? As far as I can tell the parent case is the same as the Grendel and the shoulder is only set back on the ARC .030" from the Grendel. If it is possible, is it simply done by running a Grendel case into an ARC FL die? I've got a bunch of unfired Lapua Grendel brass and it sure would be a cheap solution. I just bought a Uintah Precision upper in 6 ARC to try something new.

In all my years of reloading I've never taken brass from one caliber to another so this is completely new to me.
 

Pvt.Donut

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Apr 4, 2017
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You could, you'll probably have to do it in 2 steps. Take the neck down to 25 Cal, then down to 6mm. It would be easier to fireform 6mm PPC brass.
 

Helidriver

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Dec 6, 2009
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Well you guys were right. It was pretty straight forward. I took 25 Lapua Grendel cases (4x fired) and sized them for 6 ARC. After sizing I had to trim them quite a bit and I noticed some neck wall variations so I turned them, annealed, then steel pin tumbled. I’m going to cut open two of them just to be sure nothing unexpected has happened during the processing. Below is the result. I must say I’m pretty happy with them.

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James40004

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Oct 10, 2019
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Before you load them try an empty case to make sure it will. chamber in your rifle. Had my ppc dies to bump shoulder .002 from fired case, when I made the brass from 6.5 the base and body was too large to chamber and had to reset dies a little tighter. Ymmv

James
 

Helidriver

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Dec 6, 2009
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I finally made it to the range with my 6.5 Grendel to 6 ARC hand loads. They shot great! Starting load was averaging 2609 FPS, single digit SDs. Best group was .52 with average right at .75. My AR marksmanship needs some serious work and I know the gun would have done better if I was better tuned however it certainly exceeded my expectations.

Now I need to work up the load and get a little more speed, 2750 is my goal.
 
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FCS

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Jun 3, 2005
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I don't have a 6 ARC running yet but do have a 6mmAR. Bartlien barrel, +2 gas, 22" long and with Berger 108 MBTs in virgin Lapua brass it shoots best at 2660-2675 fps.

I suspect you'll get best accuracy and brass life with the 6 ARC at similar velocities.
 

sprad05

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Minuteman
Jan 27, 2020
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I'm running a cartidge very similar 6mm Chyeeta, and it basically uses grendel necked down to fireform, then just bumping the shoulder 3 thou after fireforming