6mm ARC Easy Mode

[Greedmoor]

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

 

[TonyTheTiger]

4. This build was hard to justify because I have a great 85 RDF load for my 18" 5.56...

Screw the 6ARC, let's hear more about this. Mag fed?

 

[Greedmoor]

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.

 

[r.tenorio671]

....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]

....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]

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.”

 

[lennyo3034]

Are those ARC groups on the top picture at 50 meters?

 

[Greedmoor]

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.

 

[Greedmoor]

Are those ARC groups on the top picture at 50 meters?

Yes, indoor range

 

[Shoots 700's]

those groups suck

 

[Greedmoor]

those groups suck

.4-.8 sucks for entry level build and first groups?

 

[Shoots 700's]

But did you confirm that they were shot at 50 yards? Are you shooting supported and prone?

 

[Greedmoor]

But did you confirm that they were shot at 50 yards?

I’m on the 50m painted line and ranged the bench at 51.5 yd so yes

 

[david walter]

I built one for momma that loves CFE223 and 108s. I have some Lever and Varget, but it’s hard to be motivated to experiment when it shoots 3/4” or so at 100 yards.

 

[Greedmoor]

I built one for momma that loves CFE223 and 108s. I have some Lever and Varget, but it’s hard to be motivated to experiment when it shoots 3/4” or so at 100 yards.

Exactly, you don’t always have to move the goal post

 

[newageroman]

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.

 

[Greedmoor]

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.

 

[newageroman]

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.

 

[Aaron.From.Winchester]

I know this is an old thread but thought I would share. I have an Odin Works 18” build that loves 108’s w/ 27.5grs BLC2, believe it or not. It’s not uncommon to get .3-.5’s. I also have good results with 27.9grs A2520, as well. LVR gives me best velocity but not quite as accurate. I am currently working on loads with Berger 95vld’s. So far, it looks promising.

 

[Dino11]

I to have had good results with the BLC2 powder, as you stated the velocity is down a little but not much.

I have run it in both gas gun and bolt action, both platforms performed very well. And it's not as dirty as Lever.

With 29.8gr I was seeing an average of 2736FPS ten shot group with 105 RFD's out of a 20" barrel, and very similar speeds out of an 18" gas gun barrel.

 

[steve podleski]

...
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.

If you load to this pressure, you will shear lugs off the bolt. My buddy and I have both lost lugs on 3 bolts using too much Varget (>27gr) with 107gr bullets. I am now following Hornady's recommended loads.

 

[Greedmoor]

If you load to this pressure, you will shear lugs off the bolt. My buddy and I have both lost lugs on 3 bolts using too much Varget (>27gr) with 107gr bullets. I am now following Hornady's recommended loads.

I’ll be back Friday with some new CFE223 data, loaded between gas and bolt max. Shooting 108 ELDm, 106 TAP seconds, 103 seconds, and 105 Barnes. Everyone mangling bolts seems to be using the 107 (you and 2 others now that I’ve witnessed)

 

[steve podleski]

I’ll be back Friday with some new CFE223 data, loaded between gas and bolt max. Shooting 108 ELDm, 106 TAP seconds, 103 seconds, and 105 Barnes. Everyone mangling bolts seems to be using the 107 (you and 2 others now that I’ve witnessed)

You will see no signs of overload on the brass. It will take hundreds of rounds before the lug comes off. I don't know if you will see any evidence of cracking on the lugs. The cracks may be small enough to see without proper diagnostic tools. I think that there is not enough 'meat' below the lugs to support the shear stresses.

 

[Greedmoor]

You will see no signs of overload on the brass. It will take hundreds of rounds before the lug comes off. I don't know if you will see any evidence of cracking on the lugs. The cracks may be small enough to see without proper diagnostic tools. I think that there is not enough 'meat' below the lugs to support the shear stresses.

Can you reply with a picture? (Here was someone’s Sharp’s bolt after too much 107/LVR 29.5+? At Pigg River)

 

[hlee]

Can you reply with a picture? (Here was someone’s Sharp’s bolt after too much 107/LVR 29.5+? At Pigg River)

Is that a nitrided bolt? I think it was @Constructor that had some choice things to say about nitriding a bolt.

 

[steve podleski]

Can you reply with a picture? (Here was someone’s Sharp’s bolt after too much 107/LVR 29.5+? At Pigg River)

Here is a pic. Sorry for the blurriness.

 

[Constructor]

Nitride treating a bolt or barrel extension after it has been gas carburized(proper heat treat) will soften the lugs allowing them to compress over time which will increase headspace. Bolts and extensions should be gas carburized(case hardened) to around 60 rockwell c but the core in the thin areas between the lugs should remain ductile so the lugs do not brake off. Nitride treating them will not completely anneal the bolts but it will soften the material.

 

[Greedmoor]

Nitride treating a bolt or barrel extension after it has been gas carburized(proper heat treat) will soften the lugs allowing them to compress over time which will increase headspace. Bolts and extensions should be gas carburized(case hardened) to around 60 rockwell c but the core in the thin areas between the lugs should remain ductile so the lugs do not brake off. Nitride treating them will not completely anneal the bolts but it will soften the material.

The one in my picture sure looked soft! At least you can tell something is happening before a random lug snap though. We need a good compilation of usage reports of all the breakages, along with positive track records with no breakages yet.

 

[AznTactical]

Can you reply with a picture? (Here was someone’s Sharp’s bolt after too much 107/LVR 29.5+? At Pigg River)

Sharps made a fully squared lug bolt version? I've never seen one and I'm a big SRC junky.

 

[steve podleski]

Here is a pic. Sorry for the blurriness.

you can see that the missing lug is next to the extractor where there is less support for the lug.

 

[Greedmoor]

Just popping in with a recent report. Still the 22" BA 6 ARC barrel and AAC 7.62 SD suppressor. I bought the 106 TAP seconds, 105 Barnes Match Burner, and some CFE 223. Loaded 29.5 (between gas and bolt max, since AA2520 worked there) and also shot a 103 eldx 2nd and 108 ELDM with that load. This was against my "control" group of 27.0 Varget/108 ELDm. I forgot my rear bag (devastated) but there were still some obvious dispersion issues directly associated with using CFE223. 10 shot for the Varget load was 1.5 MOA (at least .3 MOA bigger without proper rear support) and the other combos were all 2+ MOA for 5 shot groups (yuck).

 

[newageroman]

It still has plenty other lugs! Haaa..good to see more recent test results. I haven't shot much this past year but I have a lot of differnt batches of old ammo to shoot up before making more. On the next press run I will probably stick with the 105s and a cleaner powder than Leverevolution.

 

[steve podleski]

30.2gr of CFE223, 107CC bullet, Fed 205ARM, 26"Krieger (about 52ksi according to Quickload) =2747ave vel on a 50deg day and decent group at 600yd.