Making 6 Arc from Hornady 6.5 Grendel
#1
So 6 Arc brass is still nowhere to be found.
I'm not desperate but would really like to increase my brass count.
So..........
Turns out I have some new Hornady and new Starline 6.5 cases... maybe I could try converting some of that?
I settled on trying the hornady b/c it has the potential of being the closest case capacity to current 6 Arc, which is also Hornady.  Might try some starline sometime too if I get brave, or bored (!!)
So I also decided to use new unfired brass since I don't want to do any annealing.  I figure the new brass has "just" been annealed so doing it again shouldn't be necessary.  
I also bought the Frankford universal case trimmer, for placement on my drill (it says use a 1/2" but I have a variable 3/8 and it works fine for this.  also a drill press but that seems kind of overkill.
I was going to try to shorten the shoulder on the 6.5 die first but that didn't do anything... turns out that's not needed I can do it all with my 6 Arc die.
First I trimmed back a few cases by 0.025 (I was shooting for 0.030 which is the OAL delta but o well).   Chamfer inside and out.
Then lubed them up (RCBS case lube smeared on my fingers and then onto the case), and used the 6 Arc die (Hornady) to resize but leaving the shoulder a bit long, at 1.199" - thinking I would need to do a 2-step.  Then went to 1.185 (as it turns out).  Worked great.  I then just did a few going in 1-step from the trim to 1.185 directly and again, perfect.  The final OAL came out to 1.485, datum point on shoulder 1.185.  (The trim went down to 1.482 OAL, so the case growth during the down-size to 6mm lengthened the case only about 0.003-0.004")

So now I have 10 test cases downsized from 6.5 Grendel to 6 Arc, in new Hornady.
Some notes, this was with new brass, I imagine although don't know, that it would also work for 1x fired... how many more firings without first annealing, I don't know.
Also, don't know how this translates to, say, 6.5 Starline brass or other mfrs.  Maybe yes, maybe no, just sayin'.
Will try attach a pic of my drill "setup" pretty basic.


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#2
Any parent brass for 6mm ARC seems difficult to source as of late. Pretty sure it has been done with every option out there. I have done the 220 russian & 6.5 Grendel with good results. 6.5 Grendel conversion is the most straight forward starting point based on my experience.

Lapua 220 russian

Horinady, Lapua, Starline & PPU 6.5 grendel

7.62 x 39 of various brands.

Interested in or at least curious about your Frankfort arsenal Case trimmer.
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#3
They have a fancy, all electric, all mounted on a big box, thing.
Then there's this, you supply the electricity/mover (drill)....
Lots smaller package but all you really need.
https://www.amazon.com/dp/B07KT8D31Q?psc...ct_details

Frankford Arsenal Universal Precision Case Trimmer with HSS Construction, Drill Press or Hand Drill Functionality and Storage Case for Reloading

I use a variable speed drill, with HSS on the cutters, too fast will only dull it, so, slow-med-slow turn speed works just fine. I stuck the drill kind of upside down in one of my rifle bench-vises to hold it steady.
The case will wobble in your hand to start with, just keep the pressure (firm not too firm) against the cutter and "ride with it", when the shoulder finally bottoms out on the little inside collet, it all straightens out and the case mouth cut is pretty square. I haven't done any more trim with my hand-trimmer (more precise on the squaring-off, so to speak), figuring it will be close enough and next time I trim it will be the hand trimmer anyway.
About 64 bucks-ish from Amazon.
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