6mm ARC Easy Mode

Greedmoor

Private
Minuteman
Oct 22, 2020
28
17
El Paso
Just popping in with my build specs and results. If you were like me, you were apprehensive because there just aren't enough reports of success and plenty of videos out there trying to attribute Fuddlore theories to their shortfalls. Things like longer barrel=less accuracy, throat too long, and no-go pressure zones with less accuracy at higher speeds. If a barrel performs to a certain standard early enough, It gives me great confidence and I will advocate for it. So here's what I got:

22" Ballistic advantage with VG 6.5 brake
AR Stoner side charge upper, with left side milled as well
Aero 6.5 Grendel bolt (this is a "high pressure" bolt by the way. Small firing pin hole)
108 ELDM and Varget, AA2520 and CFE 223 tested, CCI400, Hornady 6.5 Grendel brass, first firing after conversion

Summary:
1. Ignore the published data stating 2.245" COAL... There was an obvious dispersion increase and huge pressure increase vs. 2.26"
2. The cartridge can handle 62,000 PSI just like thin bolt head 308 WIn semi autos. I have not seen many (if any) posts talking about early breakage. I am going to load as hot as this rifle can take (still below max "bolt loads") and if it breaks, I'll post about it.
3. The 108 in the Ballistic advantage wanted to make bug holes. This range session was just cruising through and seeing what works, with the first shot of each new powder falling outside the main group.
4. This build was hard to justify because I have a great 85 RDF load for my 18" 5.56... Wind and drop are not much different, but this gun will win because the groups will be less than half the size. If this was printing 1.5ish MOA groups, it would essentially be a failure. This is a super budget entry build where I really only needed a barrel, bolt, dies, and components.

The target is as follows (50m): mid left is [email protected]”/27.7 AA2520; bottom left is [email protected]”/29.2 CFE223; bottom middle is [email protected]”/27 Varget; middle right is [email protected]”/27.7 AA2520
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Greedmoor

Private
Minuteman
Oct 22, 2020
28
17
El Paso
Screw the 6ARC, let's hear more about this. Mag fed?
Lol. 18” Ballistic advantage socom barrel, LC12 brass, FED210m so far (not sure how necessary but I’m not changing) and 24.3 AA2520 for 2550 mv. A little too hot with some bolts but this one is magic headspace for it. Also has been 3-4 MOA in like 5 other barrels, but for me it’s 1.5-2 MOA and has been very predictable from El Paso to VA.
 
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r.tenorio671

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Feb 19, 2017
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13° 28' 0" N / 144° 46' 59" E
....I have some of those H108 ELDM's loaded up for charge testing w/Lever, using CBTO of 1.686" to fit my Duramax and Elander mags close to max mag length. In my early release BA barrel that will come out to approximately 0.61" jump. My intent is to load at max mag length to find charge weight then work shorter as required....I don't proscribe to "chasing the lands" theory.
 

Greedmoor

Private
Minuteman
Oct 22, 2020
28
17
El Paso
....I have some of those H108 ELDM's loaded up for charge testing w/Lever, using CBTO of 1.686" to fit my Duramax and Elander mags close to max mag length. In my early release BA barrel that will come out to approximately 0.61" jump. My intent is to load at max mag length to find charge weight then work shorter as required....I don't proscribe to "chasing the lands" theory.
In my mind the Jump needs to be as simple as possible, so I defer to the Precision Rifle Blog massive testing of all the jump lengths. The goal for my ammo is to be in the middle of the success bell curve with a 0.014" jump. If this is too far to be possible, I just keep the ammo as long as possible. Shortening from mag length when we are already a half-inch away from the lands is almost certainly going to just increase dispersion and pressure. The gun and specs left us no options, which simplifies this process.
 

hlee

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  • Jul 14, 2012
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    Those are some flaaaaat primers. And, at least one is popped. And, and you’ve got some massive craters in the non-popped primers. You’re definitely playing on the hot side of safe. So, is 1.5-2 moa you’re accuracy load? I’m not sure what to make of a load that does 3-4 moa. I’d expect better than that throwing a dart at a loading manual and saying “good ‘nuf.”
     

    Greedmoor

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    Oct 22, 2020
    28
    17
    El Paso
    Those are some flaaaaat primers. And, at least one is popped. And, and you’ve got some massive craters in the non-popped primers. You’re definitely playing on the hot side of safe. So, is 1.5-2 moa you’re accuracy load? I’m not sure what to make of a load that does 3-4 moa. I’d expect better than that throwing a dart at a loading manual and saying “good ‘nuf.”
    The primer picture is to show how much worse pressure is at the recommended 2.245” COAL. The primers on the left column haven’t even started to round with the same charges. I’m attaching the Ballistic-X group measurement and excluding the first of each 5 shot group since it IS a different powder, and I observed the first of each group as the outlier.
     

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    newageroman

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    Jul 13, 2018
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    Its a starting point. You can see it has potential. He's shooting 5 round groups, he could have easily stopped at 3 or 4 and posted those.
    I do think that is a good comparison of higher pressure primers vs not quite so much. BUT, there is that one that is pierced which is strange.
    I'd load 10 rnds of those bottom 2 groups and run them again. Thanks for the data points.
     
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    Greedmoor

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    Oct 22, 2020
    28
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    El Paso
    Its a starting point. You can see it has potential. He's shooting 5 round groups, he could have easily stopped at 3 or 4 and posted those.
    I do think that is a good comparison of higher pressure primers vs not quite so much. BUT, there is that one that is pierced which is strange.
    I'd load 10 rnds of those bottom 2 groups and run them again. Thanks for the data points.
    I see what you mean now, the primer picture was only comparing and focusing between the two columns on the right, which are the 2 COAL options. The set of brass on the far left was 2.26" and 27 Varget. It looks a little too flat, correct. I'm not sure what to do with it but many people have claimed to be here, and gas gun max is 26.7gr anyway.
     
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    newageroman

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    I havent shot Varget, but when I started and shot ppVarmit and Leverevoluion, my primers looked like the ones on the left at the high end of my ladder loads, with a couple that were just barely pierced (you could barely tell but blowing on the casemouth is a good way). I just went down about 3/4 grain.
     
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