Hornady's 6mm ARC. Who's all in?

[Tokarev]

You are not wrong the regards to total bolt thrust-it will be very similar for the ARC and Grendel as long as the PSI is the same, the Time vs Pressure curve may be slightly different but not something that an individual should/would worry about IMO.
As someone who has both 6mmARC and 6.5 grendel reamers in inventory, and has seen and used "PPC bolthead" 6.X mm wildcat AR's in play and competition for quite a while- the allure is strong in regards to the performance vs other options in the AR 15 platform but it comes at a cost in regards to the service life of bolt heads and the reliability of the associated magazines. Much like a 1911/2011 may be the perfect answer for the individual, the technical problems associated with large numbers of them makes more widespread agency issue more "Problematic" without cubic support dollars. YMMV

I've seen much posted on various boards WRT feeding issues with the various Grendel mags. Seems this (and the theoretically stronger bolt) are issues most pointed out by 6.8 SPC guys.

Hornady ballisticians mention the feeding rumors in some YouTube videos when the ARC was launched. They said they had no feeding problems when developing the cartridge using a variety of mags.

Speaking of 6.8; it was some years back I attended a VTAC Street Fighter class and used a 6.8 AR. Kyle kind of turned his nose up at me and gave me a hard time. Not in an unfriendly way. Anyway, part of the class involved shooting various parts of an automobile and my 6.8 with 110gr Pro Hunter bullets worked better than the various 5.56 guns in attendance. Kyle had to eat a bit of crow after this...

One thing he did mention was that a 5.56 rifle can have a barrel plugged with dirt that might cause the case to rupture and/or bolt carrier to fail but this wouldn't likely seriously hurt the shooter. He said this was NOT the case with 6.8. Since the exterior dimensions are the same but the internal dimensions are not a plugged barrel may result in a more catastrophic result. I never tested him on this but I certainly take his word.

This above may be why Hornady chose the 52K pressure limit.

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[Bergeron]

I think that the issue here is that cartridge development is outpacing semi-auto gun development. A gun really suited to 6ARC would need a bigger magwell and larger, stronger bolt. At that point the 22Grendel, 6ARC, and 6.5Grendel could be loaded to 5.56mm+P sort of pressure loads, and load heavy for caliber bullets long in the cases, and stuff them into new-design magazines. The problem is that it the gun would have to be bigger, in at least some dimensions, than the small frame AR. To keep weight from exceeding that of the small frame AR, such a Optimized-x39 sort of gun would need to use more modern materials, such as aluminum-magnesium-lithium alloys, carbon fiber, and polymer in creative ways, which means it would be expensive.

What kind of performance would be needed, or what kind of customers, would buy into a rifle 2-3 (or 5!) times more expensive than a 5.56mm?

As much as I like the Grendel, and the ARC, if I were going to have carbine/rifle for strictly antipersonnel purposes, and I had put 5.56x45mm out of consideration, I would probably actually lean towards 22Grendel, with 80+ grain bullets, loaded out long. The 6mm and 6.5mm versions seem more useful when medium game or very maximum range start to matter.

[Shotgun]

6mm ARC vs 6.5 Grendel feels a lot like 270 vs 30/06 circa the 1920s.

Too bad Jack O'Connor and Elmer Keith aren't here to resolve this and tell us why the Grendel or ARC is so much better than the other.

[OlongJohnson]

Jack would just say to get an AR-10 in 7-08.

[Caballoflaco]

I think that the issue here is that cartridge development is outpacing semi-auto gun development. A gun really suited to 6ARC would need a bigger magwell and larger, stronger bolt. At that point the 22Grendel, 6ARC, and 6.5Grendel could be loaded to 5.56mm+P sort of pressure loads, and load heavy for caliber bullets long in the cases, and stuff them into new-design magazines. The problem is that it the gun would have to be bigger, in at least some dimensions, than the small frame AR. To keep weight from exceeding that of the small frame AR, such a Optimized-x39 sort of gun would need to use more modern materials, such as aluminum-magnesium-lithium alloys, carbon fiber, and polymer in creative ways, which means it would be expensive.

What kind of performance would be needed, or what kind of customers, would buy into a rifle 2-3 (or 5!) times more expensive than a 5.56mm?

As much as I like the Grendel, and the ARC, if I were going to have carbine/rifle for strictly antipersonnel purposes, and I had put 5.56x45mm out of consideration, I would probably actually lean towards 22Grendel, with 80+ grain bullets, loaded out long. The 6mm and 6.5mm versions seem more useful when medium game or very maximum range start to matter.

Agreed, squeezing cartridges that can work, but are just a bit too big into an AR is a suboptimal solution. In addition to bolthead size, nobody who was trying to maximize reliability would design a firearm from the ground up that stacks rounds in the mags like we see with the x39 or .30 Remington based cartridges.

[Skinner Precision, LLC]

I've seen much posted on various boards WRT feeding issues with the various Grendel mags. Seems this (and the theoretically stronger bolt) are issues most pointed out by 6.8 SPC guys.

Hornady ballisticians mention the feeding rumors in some YouTube videos when the ARC was launched. They said they had no feeding problems when developing the cartridge using a variety of mags.

Speaking of 6.8; it was some years back I attended a VTAC Street Fighter class and used a 6.8 AR. Kyle kind of turned his nose up at me and gave me a hard time. Not in an unfriendly way. Anyway, part of the class involved shooting various parts of an automobile and my 6.8 with 110gr Pro Hunter bullets worked better than the various 5.56 guns in attendance. Kyle had to eat a bit of crow after this...

One thing he did mention was that a 5.56 rifle can have a barrel plugged with dirt that might cause the case to rupture and/or bolt carrier to fail but this wouldn't likely seriously hurt the shooter. He said this was NOT the case with 6.8. Since the exterior dimensions are the same but the internal dimensions are not a plugged barrel may result in a more catastrophic result. I never tested him on this but I certainly take his word.

This above may be why Hornady chose the 52K pressure limit.

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6mmARC is simply a standardization of something that has been around much longer. The first time I held a 6mm grendel based reamer in my hand was 2007 IRC. The first time I was on the line next to a competitor shooting a 6mm PPC based AR was before 2000 and the first time I recall a 6mm Grendel based AR in "PRS type" match was the Snipershide Cup about 2008. I am a fan of Grendel based cartridge's, my personal collection has some. I own no 6.8 SPC based rifles personally, I have a .224 valk reamer for customers but never even bothered to get my 6.8 SPC II reamer back from the last person it was lent too, so I am far from a 6.8 fanboy. I also have seen grendel based guns used by a wide variety of builders, not all were plug and play. I do not doubt Hornady's Engineer's findings or integrity but based on observations of a not small pool of diverse but similar cartridge's/ ammo / weapons components I stand by my assertion that big organization adoption is very likely to be harder for the ARC logistically, individuals not such a big a deal. This situation is very similar to the fact that yesterday I carried my STI as an "enthusiast/individual" with confidence but wouldn't recommend it to an agency for mass issue if they were silly enough to ask my opinion....

Bolt life can be an issue with high volume 5.56 shooters, I do not have first hand experience on the .mil/LE side of higher round count lug failures but have seen lugs fail firsthand for high volume competitors. There are many fewer 6.8's and 6.5's out there but many more "per capita" results reported by shooters on the interwebs for both larger cartridge's. The million dollar question is is it because the diminished margins associated with the larger cartridge's or is it because people picked them for higher performance than otherwise available in an AR and then pushed that too far in the search of said. Hornady's 52KSI max pressure is not that far of the Valk's SAAMI listed max of 55 KSI and same the Grendels MAP of 52 KSI, I am not sure I can think of any AR 15 chamber larger than a .373 boltface that allows much more than 55KSI excluding the highley modified bolt / barrel extensions/ sometimes upper receiver modifications associated with the various 6mm BR / WSSM/ 22-250 attempts.

[Shotgun]

Jack would just say to get an AR-10 in 7-08.

Perhaps. But, whatever he advised, it would be from atop a picturesque mountain with an unbelievably big sheep in the foreground.

https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD

[Tokarev]

6mmARC is simply a standardization of something that has been around much longer. I do not doubt Hornady's Engineer's findings or integrity but based on observations of a not small pool of diverse but similar cartridge's/ ammo / weapons components I stand by my assertion that big organization adoption is very likely to be harder for the ARC logistically, individuals not such a big a deal.

Hornady says in one of the introductory videos that they did not invent the 6mm Grendel but rather tweaked a few things and standardized it, as you say. Design specs were to give trajectory not unlike that of a 308/AR10 but in a standard AR platform. In this case it looks like the ARC hits the bill as likely would have some other similar cartridges. And I don't think the 6 ARC is meant to be anything other than a limited application and/or stop gap until something happens with the new 6.8 and the new rifle to accompany. Will it grow beyond this role if and when the 6.8 rifle project fails?

[Borderland]

Perhaps. But, whatever he advised, it would be from atop a picturesque mountain with an unbelievably big sheep in the foreground.

https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD

Jack would have looked at an AR and said WTF. That isn't going on a sheep hunt with me unless it can chamber a .270.

[LJP]

I’m interested, but primarily because Hornady is behind it (I own a 6.5 Creedmoor bolt gun for the same reason), and because I live in an AWB state where I cannot obtain new lower receivers, but a new upper in a different caliber is not an issue. Hopefully the supply chain opens up someday and I can pick up an upper and some ammo.