New 6mm Advanced Rifle Cartridge

[Varminterror]

They definitely should have done this on the SPC case family. The comblock case family is a scourge for ARs, especially at high pressure.

It’s been done in multiple iterations, the 6-6.8 variants are out there, and they can’t deliver the same performance with the heavy, high BC bullets. The 6 WOA, 6 Hagar, 6 PDK, 6-6.8, and 6 DTI are examples. Long ogive bullets don’t fit within mag length. I’ve thoroughly enjoyed the 6WOA (and 6-45) with lighter bullets for coyotes in the past, and the blistering speeds with 75-87grn bullets are great for short to mid-range shooting. But they give up a lot of speed quickly compared to the high BC 105+ pills.

The 24 Nosler is the only case I have seen which pushed the SPC shoulder back to fit the heavies into mag length, but there simply isn’t enough case capacity left when you give up that length in the skinnier SPC case. That was the failing of the 24 Nosler (well, one of its failings at least) - they trimmed the SPC case back to 1.6”, which still didn’t fit most of the 105+ bullets into mag length, and the result was terribly anemic. The skinnier 6.8 SPC case might reduce bolt thrust, but it gives up too much capacity when you make room out front for long ogive bullets. They tried to push the pressure up to make back the difference, but it didn’t pan out. The 24 Nosler has almost 25% less case capacity than the 243LBC/6mmAR, despite a 10th inch longer case. I expect still over 20% less than the resulting capacity of the new 6ARC. As @Gtscotty noted - even at higher pressure, the smaller 24 Nosler case fell short of what we’re seeing with the 6 Grendel variants (although incorrectly citing the 24 Nosler as the “exact critter,” since it’s considerably different in many ways). Running 2300-2400 with the 105’s is pretty lackluster. For lighter bullets which fit into mag length, the 6-45 has larger capacity even than the 24 Nosler, and of course, doesn’t require special mags or bolts, or sparsely available, expensive brass. The 24 Nosler was a non-starter.

 

[Gtscotty]

Over on The Hide someone posted a picture of Hornady stamped 6mm ARC brass, seems like a pretty clear indicator of who was behind the SAAMI standardization.

 

[Varminterror]

Over on The Hide someone posted a picture of Hornady stamped 6mm ARC brass, seems like a pretty clear indicator of who was behind the SAAMI standardization.

Odd that they haven’t released anything about it yet. This is a pretty broad deviation from their last few launches. Have to ask - which company is building the rifles, and are they behind schedule? Equally, are they postponing announcement to get out of the CV economic valley we’re in?

Photo credit to Rex over at the Hide:

 

[Llama Bob]

It’s been done in multiple iterations, the 6-6.8 variants are out there, and they can’t deliver the same performance with the heavy, high BC bullets. The 6 WOA, 6 Hagar, 6 PDK, 6-6.8, and 6 DTI are examples. Long ogive bullets don’t fit within mag length. I’ve thoroughly enjoyed the 6WOA (and 6-45) with lighter bullets for coyotes in the past, and the blistering speeds with 75-87grn bullets are great for short to mid-range shooting. But they give up a lot of speed quickly compared to the high BC 105+ pills.

The 24 Nosler is the only case I have seen which pushed the SPC shoulder back to fit the heavies into mag length, but there simply isn’t enough case capacity left when you give up that length in the skinnier SPC case. That was the failing of the 24 Nosler (well, one of its failings at least) - they trimmed the SPC case back to 1.6”, which still didn’t fit most of the 105+ bullets into mag length, and the result was terribly anemic. The skinnier 6.8 SPC case might reduce bolt thrust, but it gives up too much capacity when you make room out front for long ogive bullets. They tried to push the pressure up to make back the difference, but it didn’t pan out. The 24 Nosler has almost 25% less case capacity than the 243LBC/6mmAR, despite a 10th inch longer case. I expect still over 20% less than the resulting capacity of the new 6ARC. As @Gtscotty noted - even at higher pressure, the smaller 24 Nosler case fell short of what we’re seeing with the 6 Grendel variants (although incorrectly citing the 24 Nosler as the “exact critter,” since it’s considerably different in many ways). Running 2300-2400 with the 105’s is pretty lackluster. For lighter bullets which fit into mag length, the 6-45 has larger capacity even than the 24 Nosler, and of course, doesn’t require special mags or bolts, or sparsely available, expensive brass. The 24 Nosler was a non-starter.

The problem is that when you load to a constant bolt thrust, the comblock case buys you nothing. You get more capacity, but lose it back reducing pressure to get bolt thrust the same. You can do anything with the SPC case (with the shoulder wherever you want) that you can with the comblock case, with better feeding and more material remaining in the bolt. All supposed additional performance with the Grendel simply comes from bolt-breaking over-thrust.

The combloc case is pure loss absent a custom bolt and barrel extension designed to retain bolt strength. That would have been the right thing to do for the Grendel, but Bill Alexander is incompetent and screwed it up and here we are...

 

[Varminterror]

You can do anything with the SPC case (with the shoulder wherever you want) that you can with the comblock case

Real-world data proves this is false. When you fit mag length with long bullets, you can’t get enough powder into the skinnier SPC case. The 24 Nosler loads to higher pressure than the Grendel variants, and falls 200fps short.
You can pretend the rebated rim reduces the bolt thrust, but it doesn’t. The pressure surface is the interior face of the case head. The 24 Nosler has 5.7% greater pressure, exposed over 5.2% reduced internal head face area. A wash at best.

So the 24 Nosler runs the same bolt thrust as the 6mmAR/243LBC, has a ~0.1” longer case and can’t seat many of the long Ogive bullets which can the Grendel variants, and then the Nosler runs 200fps slower...

Of course, your continued retort is that the Grendel case breaks bolts, because it does, indeed, have a larger cut in the bolt face, however... thousands on thousands of Grendel owners have ran hundreds of thousands if not millions of rounds without experiencing an increase in bolt failures vs. any other AR cartridge.

It’s a tired line, and a person has to be delusional to believe it.

 

[Gtscotty]

Odd that they haven’t released anything about it yet. This is a pretty broad deviation from their last few launches. Have to ask - which company is building the rifles, and are they behind schedule? Equally, are they postponing announcement to get out of the CV economic valley we’re in?

Photo credit to Rex over at the Hide:

View attachment 899605

This would be the obvious guess, there's no way I'd introduce anything right now while the world is busy peeing itself over Chinese beer flu and cratering markets.

Get SAAMI standardization through in late January, get rifle/barrel manufacturers spun up for a spring intro then... Hmmmm... maybe wait a few months and hope the dumpster fire has died down a bit.

 

[Llama Bob]

It’s a tired line, and a person has to be delusional to believe it.

Grendel defenders are jokes It's junk engineering, and that's easy to prove. Simply do the stress analysis on the bolt, like Bill Alexander was too unskilled to do. And you'll find that you can run the SPC case FAR FAR hotter than the Grendel case with less bolt failure not just due to smaller piston diameter, but due to far more material in the bolt.

The Grendel is flat out stupid. Bill Alexander was run out of the industry for his incompetence. Those that continue to pimp his shoddy wares are victims of a con man at best and enabling his con in reality since the physics are now well understood by everyone but those who willfully ignore the facts

 

[Demi-human]

And you'll find that you can run the SPC case FAR FAR hotter than the Grendel case

Which one?
Spc, SpcII, 6.8AARP, 6.8x43?

The SPC II chamber and 6.8 ARP and 6.8x43 chambers all have a redesigned throat and leade, and generally slower twist. Any of the common chambers SPC II and later can handle the higher pressure factory loads that used to be sold such as the SSA "Tactical" loads. I don't know of any manufacturer's that are still putting out the original SAAMI spec chambers, and most, such as ARP, Rock River, Bison Armory, Stag, Radical Firearms and PSA will clearly identify the chamber spec they are using.

"It is not the critic who counts; not the man who points out how the strong man stumbles, or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood; who strives valiantly; who errs, who comes short again and again, because there is no effort without error and shortcoming; but who does actually strive to do the deeds; who knows great enthusiasms, the great devotions; who spends himself in a worthy cause; who at the best knows in the end the triumph of high achievement, and who at the worst, if he fails, at least fails while daring greatly,…"

"Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure, than to rank with those poor spirits who neither enjoy nor suffer much, because they live in the gray twilight that knows not victory nor defeat."

Theodore Roosevelt


Have you got the reamer yet for the 6mm Llama?

 

[JFrank]

I just posted this on another forum and figured they're might be some folks interested here as well. SAAMI just added a 6mm Grendel derivative called the 6mm Advanced Rifle Cartridge or 6mm ARC to their newly accepted cartridges list.

6mm ARC introduction pdf

The case looks like the shoulder has been moved back, and the neck is a little shorter as compared to a Grendel case. The published instrumental velocity shows 2,700 fps for a 108gr bullet.

I'm curious if Hornady is behind the standardization of this cartridge, the name seems to fit the current convention (PRC vs ARC), and the published velocity utilized a 108gr bullet as opposed to 105gr or 110gr.

Anyway, it's interesting to see a 6mm Grendel becoming SAAMI standardized, hopefully AR barrels in this chambering will start flowing soon.

Kinda looks like this one.

 

[Llama Bob]

Which one?
Spc, SpcII, 6.8AARP, 6.8x43?

You're missing the point. The is not a 6.8SPC vs 6.5 Grendel discussion. It is a SPC case vs. comblock case discussion. The question here is which case gives more velocity in the AR platform for the same risk of bolt breakage with the same bolt material when adapted for long 6mm bullets, and the answer is the SPC case is superior due to engineering errors made by Bill Alexander (and previously Colt) when adapting the comblock case to the AR. With a hypothetical custom barrel extension and bolt, the comblock case would win. But those parts don't exist.

 

[Varminterror]

you'll find that you can run the SPC case FAR FAR hotter than the Grendel case

What powder are YOU running in YOUR 24 Nosler which yields 105’s or 108’s at 2700+ fps from a 24” barrel?

 

[Llama Bob]

What powder are YOU running in YOUR 24 Nosler which yields 105’s or 108’s at 2700+ fps from a 24” barrel?

I don't run an 24 Nosler. I run a 6mmHAGAR variant. Every single one of the berger 105s fits at mag length. Case capacity is 36.0 GR H20. My barrel isn't 24 inches, but there are 20+ powders that would do what you describe. You could get over 2800 if you were willing to tolerate RL-17's quirks. I personally use H4895.



Again, the Grendel meets the reality that it's bolt breaking garbage and anything well designed stomps it The things it supposedly does are done MUCH, MUCH better on the SPC case. That's just the engineering.

 

[Gtscotty]

I don't run an 24 Nosler. I run a 6mmAR variant. Every single one of the berger 105s fits at mag length. Case capacity is 36.0 GR H20. My barrel isn't 24 inches, but there are 20+ powders that would do what you describe. You could get over 2800 if you were willing to tolerate RL-17's quirks. I personally use H4895.

View attachment 899764

Again, the Grendel meets the reality that it's bolt breaking garbage and anything well designed stomps it The things it supposedly does are done MUCH, MUCH better on the SPC case. That's just the engineering.

6mmAR is a necked down Grendel...

 

[Llama Bob]

Sorry, should have typed HAGAR. It's early here. It's basically a HAGAR case with a neck like a 6mm AR. It's SPC brass, bolt, and bolt thrust.

The problem with the 24 nosler is the neck is too long.

 

[Llama Bob]

I'd have to go look at the exact dimensions, but the case OAL comes right to the ogive of the 105 Beger at 2.25, shoulder is 35deg, neck is min length - maybe .22 or .23? There was a basic SPC brass run that worked for it at one point.

 

[Varminterror]

The problem with the 24 nosler is the case is too small.

Fixed it for you.

Of note, for those playing the home game - since his Grendel based 6mmAR (as depicted in the Quickload photo) suddenly became an SPC Hagar... the Hagar has a trim length of 1.765”. The Berger 105 Hybrid has a 0.731” nose length. So minimum COAL for the 105 Hybrid in the Hagar case is 2.496”. Given 4thousandths clearance to slide in the mags, that would be 0.2” longer than mag length...

Again, you’re simply not going to get the heavy 105-109 6mm bullets into AR-15 mag length in a shortened SPC variant and still have enough case capacity to exceed the 6mm Grendel variants.

 

[Llama Bob]

If you read what I posed, you'd realize you're still full of it (which is a pattern here). It's a variant of the SPC case. OAL is 1.55 IIRC which lets you shoot bergers with a 0.7" nose (all 105s) at 2.26 with a hundreth to spare.

Seriosuly, I have never seen anyone go farther than you to defend Bill Alexander's scam. Does he owe you money you're still hoping to collect? You wouldn't be the only one...

 

[Varminterror]

Here’s what happens when heavy bullets are loaded to mag length in the Hagar.

 

[Llama Bob]

Some of those are past the ogive, which is why the verion I shoot is OAL 1.55, shorter neck, and 35deg to get the capacity back. Works like a charm. You just have to start from basic brass.

There's not actually any real downside to having a bullet base down in the case.

 

[Varminterror]

Full length 6 Hagar is made from the 30 Rem, not 6.8 spc. A 6-6.8 variant as you’re describing would have to have a shortened neck, but as I addressed above, the capacity simply isn’t there when you seat bullets to deliver “far more” than the Grendel case. I’ve owned the 6 WOA, within spitting distance of what you’re describing - except mine had a LARGER CASE - and I still wasn’t getting the speed I get from a 243LBC when loaded to mag length. Raw water capacity was about the same, but I can fit more powder into the fatter Grendel case than I could the 6 WOA - same problem there, all of my single feed length 107/105 WOA loads were compressed - no room to ramp pressure high enough to really exceed the 2800-2900fps mark I’m getting with the 243LBC. Certainly not exceeding what can be done with the blown out Grendel variants like 6 FatRat or Turbo40. “There’s no replacement for displacement.”

Even if your fantasy here is real - which my personal experience suggests it isn’t - you’re describing a non-standardized cartridge with custom reamers and dies, with relatively poor quality brass in market which relies on highly compressed loads to produce unnecessarily high pressures and increased bolt thrust to reach the same performance as a now SAAMI standardized cartridge which hits those marks in street shoes, and has Lapua brass available.

 

[Llama Bob]

You saw the load list - nothing over 105%, tons of fast loads, and nothing over 55KPSI. What pressure is this 6mm ARC supposed to run at?

It's clear you live in a fantasy world when it comes to Bill Alexander and his little joke on the shooting community. That's fine. Everyone needs a hobby. But don't pretend that the engineering supports you, because it doesn't.

 

[Llama Bob]

Full length 6 Hagar is made from the 30 Rem, not 6.8 spc.

Apparently you missed the comment about "basic brass" - yes, I'm well aware you don't actually start from 6.8 SPC.

I think this discussion is worthless. You have no interest in cartridge engineering, nor in actually reading what's written. You've just got it in your head to support Bill's little joke on you.

 

[Llama Bob]

I found the SAAMI doc for 6mm ARC, and it looks like 52KPSI. So basically the same bolt thrust as a 55KPSI SPC case. BUT, and this is an enormous BUT, with extra material removed from the bolt for the bigger case head.

So in fact the 6mm ARC offers not only no improvement in performance, but an increase in bolt breakage. It truly is a cartridge Bill would be proud of

 

[Gtscotty]

Don't get my thread closed with this stupid bickering. I want the thread to remain open so we can post more info on the case as it comes out.

 

[Demi-human]

(Redacted. With respect.)