Grendel to ARC Brass

[BassinDmax]

Without something to use as a comparator you are only guessing. If you have a head space gauge you can perhaps come up with a bushing that fits over the neck, allowing the bushing to stop pn your shoulder. Then measure a reference distance from the base of your case to the opposite end of the bushing that contacts the shoulder that establishes your head space. All this is assuming you have a caliper and are comfortable using it.

If this works out for you you can also use the same bushing to reference your Go- head space gauge. Id shoot for .004 clearance give or take .002".

Another option is a case gauge or a comparator neither will do you much good without a head space gauge or fired case for comparison.

https://www.whiddengunworks.com/product/case-gauge-3/

https://www.whiddengunworks.com/product/...ump-gauge/

How precise do you wish to get? for your consideration a Whiddnen click adjustable full length bump die.

https://www.whiddengunworks.com/product/...ing-kit-2/

Might have helped to provide more info with my question, yes I'm new to the ARC and re-forming a different case to the ARC, but I'm not new to reloading. I'm far from an expert, but do have a good understanding of headspace and it's impact on reloading and case life. I have the Hornady Comparator and very comfortable with it's use and the use of calipers. I usually make my own modified case's, but I bought a Hornady modified case in the absence of a fired case to work with. I also have a Wilson Case Gage for the ARC. I pretty much have everything I need minus the barrel. I have the Hornady die set for the ARC and also purchased a Wilson full length bushing die. My plan is to use the Hornady full length die to form the brass and then use the bushing die to set next tension on successive reloads.

Based on the tools I have, can I bump the shoulder, without over-sizing, until it goes smoothly in and out of the case gage? If I did this on about 10 cases to start with and then fired formed them I would then have fired case dimensions for my barrel? Or should I wait for the barrel and insure they'll cycle properly before fire forming?

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make sure you anneal the Grendel brass,  trim the FLS grendel brass back to 1.483 and run the Arc dies

Even on new Lapua brass that's been annealed by the factory? I do anneal all my brass after every firing, but wasn't sure I needed to do it on Lapua brass prior to forming.

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When I started on my 400 pieces, I bumped 5 back to SAAMI minimum of 1.183 base to B comparator line. Used them for my initial function check and then was able to use the fired measurement for sizing the rest. If you size all of them down to SAAMI minimum, you would possibly be subjecting your brass to unneeded stretch, but any virgin ARC brass would also be at SAAMI minimum (or below) - as would any brass in factory ammo. In my case, my Lilja chamber is 1.188 and I bump them to 1.185, so if I had bumped them all to 1.183, it wouldn't have had an impact on my brass life.

While you ponder that, fire up the trimmer! Your going to need to take 0.03" off and take them down to 1.480" OAL, and you should do this before you bump down since the longer Grendel brass could hit the top of your die. It did with my Hornady die and I lost a couple to dimples on the shoulder.  The trimming is the vast majority of the work. You could/should do your chamfering/deburring too. After that it's just a quick lube on the shoulder and inside/outside of the neck and through the sizer.

Good points, I'll start with about 10 cases at most. Thanks for the heads up on trimming, I'll pull out the old RCBS trimmer and trim them all to 1.480". I normally use the WFT2 to trim, however don't have the Grendel insert. I guess after trimming a few my arm will tell me if I need to order the Grendel insert