Hornady 6mm ARC "New" cartridge

[Dusty Stevens]

Only the Special Forces communities (and JSOC) have the sourcing independence to take on anything new with any agility. Big Army is so dominated by politics and ineptitude that it's a herculean effort just to get it the staff to formally agree that the sky is blue.

The USMC is slightly more agile (and stubborn) in persisting with their own acquisitions.

I don't think DoD participation moves the needle (yet) for 6 ARC and in same ways can work against a cartridge that might otherwise be excellent.

I still havent seen the creedmoor replace the 308 like it was supposed to. What ever happened to the 6.8spc? I guess by saying the military will be evaluating it maybe someday itll sell

 

[nakneker]

This will probably a full onslaught marketing campaign, I like the Creedmoor but I’m tired of hearing about it, evening hearing “Creedmoor” wears me out.

That being said I ordered a 100 roundsof 6 ARC, a 21” ARC barrel, and found the dies. I’m new to ARs and started building uppers this year. I think it’ll be fun to play with the ARC on this platform, if I like it I’ll have bolt gun chambered up. It’s not about “needing” anything, I have PPCs and BR rifles that have that covered, just sound fun to me.

I’m sure the one is gonna have its share of haters.

 

[shoot4fun]

I guess I don't understand your safety concern. Anyone trying to use ARC ammo in their 6mm Grendel variants would likely get light primer strikes, or at best case-stretched fire-formed brass. A 6.5 Grendel, the closest SAAMI standardized factory cartridge, will not chamber due to the longer headspace. That was probably done intentionally by Hornady to avoid the too-big a bullet trying to go down the 6mm bore safety issue, and appears to be standard industry practice (bigger bullet can't go down the smaller bore: e.g. 270 vs 280). All combinations of .441 case-head ammuniton will either not chamber, or will chamber but not fit right and send a correct or smaller bullet down the bore. Seems as safe as any existing cartridge offerings to me.

0.020" might as well be a mile when we are talking about headspace dimensions. The ARC is not the Grendel/AR/LBC/FatRat/Grinch/etc. and it is standard operating procedure to only chamber ammunition designed for the name marked on the barrel. Many factory rounds can chamber in rifles that they are not meant for and it is up to the consumer to avoid trying it. This isn't a new issue and has existed forever. A 243 will chamber and fire in a 260 and I don't recall many people suggesting Remington was being reckless offering the 260. Same story for a 244mm Remington and the 257 Roberts, IIRC. These are all SAAMI standardized offerings too, not custom non-standard chambers offered by boutique gun makers.

I was with someone on a prairie dog shoot who managed to chamber and fire a 300BLK round in a 22-250 bolt gun. That could have been disastrous had it not been a very strongly made action with a three-lug bolt. It blew the Sako-style extractor out, took out the detachable mag bottom and put a slight swell in the barrel just ahead of the chamber. The bullet was swaged from .308 down to the .224 barrel diameter and lengthened to about 1 1/2" long.
It isn't confined to rifles either. I have seen 40 S&W loaded rounds chambered in 45ACP pistols, only to have the live round fall out when the pistol was inserted into a holster. I have seen 44 Magnum rounds fired in a 45 Colt revolver. As many rounds as I've seen in my lifetime of range/match work if it could be at all possible someone did it.
The ultimate responsibility is on the individual.

 

[shoot4fun]

I still havent seen the creedmoor replace the 308 like it was supposed to. What ever happened to the 6.8spc? I guess by saying the military will be evaluating it maybe someday itll sell

Get over it my friend!
The 6.5 Creedmoor was never made or marketed to be used by military and the only connotation of "replacing the 308" ever, even subtly, was that it was designed to feed effortlessly thru the AR-10 type rifle/magazine.
The 6.8SPC was indeed another story. It was designed, IIRC, by some military guys and touted as the perfect replacement for the 5.56 NATO. It was used by some secret squirrels in far away places and may still be. The US Military consult with you before they put new guns/ammo into play?

 

[Dusty Stevens]

Get over it my friend!
The 6.5 Creedmoor was never made or marketed to be used by military and the only connotation of "replacing the 308" ever, even subtly, was that it was designed to feed effortlessly thru the AR-10 type rifle/magazine.
The 6.8SPC was indeed another story. It was designed, IIRC, by some military guys and touted as the perfect replacement for the 5.56 NATO. It was used by some secret squirrels in far away places and may still be. The US Military consult with you before they put new guns/ammo into play?

You may want to take a chill pill there turbo. I never put forth any theories. The creedmoor was brought along as going to be adopted shortly by socom and this new one has the same feel. Not sure why you jumped on me- im happy about the creedmoor and this new one. I bet you honk your horn in traffic jams

 

[shoot4fun]

You may want to take a chill pill there turbo. I never put forth any theories. The creedmoor was brought along as going to be adopted shortly by socom and this new one has the same feel. Not sure why you jumped on me- im happy about the creedmoor and this new one. I bet you honk your horn in traffic jams

ouch
You really got me there.

 

[Adam in WI]

The 6.8 is a fine round in it's own right in spite of Remington's early efforts with it. Love my 18" ARP 3R.

 

[shoot4fun]

The 6.8 is a fine round in it's own right in spite of Remington's early efforts with it. Love my 18" ARP 3R.

My understanding is their are now two variants of the SPC. IIRC, the ARP uses the newer version and can handle higher pressures.
There is no doubt the 6.8SPC was pointed toward military use. After all, it was the brainchild of two active AMU gunsmiths.
Also, contrary to what some here think, word is the US Military is quietly conveying some of the M4A1 and M249 SAW rifles over to the caliber.
New 6.8 mm Round a Game-Changer for Ground Troopswww.nationaldefensemagazine.org › articles › new-68-...
Will it succeed? Only time will tell. Will it be adopted widely? Well, only the money trail will tell.

 

[243Mendoza]

One issue that the military or other users of the 6ARC may be bolt lug failure. I have been shooting the 243LBC AR 40 (a variation of the the 6AR) for the past 3 years with about 3900 rounds through the barrel shooting 105gr bullets. I have had 2 bolt lug failures with a Alexander Arms bolt and a JP bolt. A friend, shooting the Fat Rat ( a variaton of the 6AR Turbo 40), has had 1 failure. We have now reduced our load to give about 2750fps or less with 105 and 107gr bullets through 24 and 26" Krieger barrels.

 

[Hohn]

I still havent seen the creedmoor replace the 308 like it was supposed to. What ever happened to the 6.8spc? I guess by saying the military will be evaluating it maybe someday itll sell

I suspect that they send ideas to the military unsolicited at times just so they can market something as being “developed for an elite US military unit.”

I’m sure the military kicks tires all the time. But not nearly to the extent the marketing folks would have us believe.

 

[shoot4fun]

One issue that the military or other users of the 6ARC may be bolt lug failure. I have been shooting the 243LBC AR 40 (a variation of the the 6AR) for the past 3 years with about 3900 rounds through the barrel shooting 105gr bullets. I have had 2 bolt lug failures with a Alexander Arms bolt and a JP bolt. A friend, shooting the Fat Rat ( a variaton of the 6AR Turbo 40), has had 1 failure. We have now reduced our load to give about 2750fps or less with 105 and 107gr bullets through 24 and 26" Krieger barrels.

I'd be interested in knowing your thoughts on exactly what caused those failures. Is it due to the pressure slamming the case head back against the bolt or maybe a premature unlocking of the lugs? Could it also be caused by improper buffer weight or spring?
The issues I have seen that caused bolt lug failures in 5.56 AR's was due to over-gasing issues.

 

[ASbobcat]

One issue that the military or other users of the 6ARC may be bolt lug failure. I have been shooting the 243LBC AR 40 (a variation of the the 6AR) for the past 3 years with about 3900 rounds through the barrel shooting 105gr bullets. I have had 2 bolt lug failures with a Alexander Arms bolt and a JP bolt. A friend, shooting the Fat Rat ( a variaton of the 6AR Turbo 40), has had 1 failure. We have now reduced our load to give about 2750fps or less with 105 and 107gr bullets through 24 and 26" Krieger barrels.

Available product information infers that the lower 52Kpsi SAAMI limit was chosen for this very reason, citing "durability".

This allows potential for greater performance in bolt guns, making the cartridge even more interesting to some.

 

[ASbobcat]

So who has a 24" AR Barrel and dies. Lets get a goin!

Sinclair/Brownells

 

[243Mendoza]

I'd be interested in knowing your thoughts on exactly what caused those failures. Is it due to the pressure slamming the case head back against the bolt or maybe a premature unlocking of the lugs? Could it also be caused by improper buffer weight or spring?
The issues I have seen that caused bolt lug failures in 5.56 AR's was due to over-gasing issues.

I do not know 100% the cause of failure but I suspect too much pressure. I bought the rifle from another competitor who told me the cartridge was turbo version which can hold more powder so I handloaded accordingly but I saw severe ejector marks on the brass so I put in a stiffer recoil spring, heavier buffer and BCG...result was a busted lug. Then I find that the cartridge was not a turbo so I loaded with less powder so the ejector swipes were gone but after a few months, another lug gone but JP replaced it for free. I am now handloading with 28gr of H4895 which was less than before and if this bolt fails, I will get a bolt that has a shallower face giving more material for lug support.

 

[SG4247]

So, my posts arent pure internet keyboard jocky stuff.

I am very intimate with the 6AR. Love the round... burn about 1000 a year in competition. Have several reamers in the 6AR profile.

But, common 6mmAR problems as I mentioned earlier:

1. Magazines - few work well - due to case taper, I make my own 20 rounder. Plastic mags = no go.
2. Feeding - Long slender 6mm bullets dont feed well, especially big fat short brass cases in poorly adapted .223 mags.
3. Headspace - too much is a problem, see #5. Hornady traditionally makes their Grendel ammo very short.
4. Type 1 and type 2 bolts - .010" difference - still causes confusion in the AR crowd after all these years.
5. Bolt durability - ouch! Broke em all. Now just replace the bolt new every 750 rounds.
6. Primers - pierced and ejected primers - had that even with factory 6.5 Grendel ammo. Flat primers in 6mmAR using Lapua and Hornady Grendel Brass is standard.

Now the Positive:

Round is awesome if done right.

6mmAR Pistol
11.5" Brux barrel launches 6mm 105 Bergers at 2350 fps.
Has three club records.
Beaten the .223 AR rifles in heads up competition!
Kills 52lb RAM steel silhouettes at 547 yards.

Compare the wind drift of my 11.5" 6AR pistol with 105 Bergers at 2345, to a 18" .223 with 77 SMKs.

Imagine what it does at 26".

 

[Henryrifle]

I received a 20" Ballistic Advantage DMR profile barrel from Brownells yesterday and attached it to an upper that had previously been a 6.5 Grendel that I never shot. Looking through the barrel with a borscope, it looked pretty good. The chamber looks straight and the land ramps all start at the same distance from the neck. Maybe this is always the case but the gas port is drilled in the middle of a land. Seems like that would be better in one of the grooves. Ammunition and dies are on backorder but I really wanted to take a few shots. I chucked the 6.5 Grendel die in the lathe and took .035 off the bottom. Using the saami specs, I moved the shoulders back on the Grendel cases and built a small Redding neck bushing holder to size the necks down to 6mm size. I also had to trim the necks pretty significantly. Moving the shoulder back .03 did cause some dimpling/buckling in the shoulders but not terrible. My bushing holder also induced some significant loaded cartridge runout--as much at .017" in the worst cases but all had at least .005". After checking 25 of these for feeding and ejection I loaded them with 105 Berger hybrid targets and 27.5 grains of H4895 to magazine length.

The rifle functioned perfectly ejecting brass at 2:30 and feeding without issue from a E-Lander 10-round Grendel magazine. Using the Labrador I quickly realized that I needed to download the next test by .8 to 1.1 grains. Velocity was in the high 2720 FPS range with a few shots maxing out at 2740 FPS. Moderate to significant ejector swipes are visible on all cases. SDs for the five 5-shot groups were pretty good and between 6-7 FPS. The group sizes were disappointing averaging 1.75 MOA at 100 yards with the best being 1.125 MOA, but I'll reserve judgement until using proper brass is loaded at a more reasonable 2650 FPS.

I shot from prone using a F-T/R joypod and a rear bag. Recoil was very moderate and staying on target after the shot was achieved most of the time. I did shoulder and cheek the rifle as well as wrapped my hand around the grip. Will update after next test in a few days. Looking forward to correct dies and some factory ammo to test. Would be great if factory ammo shoots in the .5 to .7 range.

Henryrifle

 

[dcali]

i was thinking safety mainly. If I was the head engineer at Hornady and wanted a unique cartridge based on existing wildcat architecture, I am making it where it wont even chamber and go into battery in any existing wildcats or production chambers for safety reasons. This 6ARC will chamber and fire (Unsafely) in prolly a dozen existing production Grendel style chambers that I can think of. Not even going into the type 1 and type 2 bolt conversation here...that makes this all much worse.

So, I would have seriously considered making the shoulder like .035 longer, than Grendel saami. More options for performance and way safer for the public. Not an issue really for military use, if thats their market focus.

.02

I agree - that would be wise. I also think that if you're considering this sort of problem, it's a sign that you're reinventing the wheel.

 

[Evan]

I agree - that would be wise. I also think that if you're considering this sort of problem, it's a sign that you're reinventing the wheel.

I think the way Hornady made it headspace shorter is safer than if they made it longer:

If somebody takes 6mm ARC factory ammunition and tries to fire it in a 6mm Grendel rifle (a reasonable possibility for someone ignorant) - it chambers fine, the bolt can close and lock up properly - helping prevent an out-of-battery discharge - and it may or may not fire due to the probable light primer strike. If it fires, you get case stretch and at worst the case ruptures, gas is diverted back through the action and leaves part of the case in the chamber as the case head is extracted. Most of the time this should result in no injury to the shooter, as most rifle systems are designed to safely handle this kind of case failure.

If Hornady made the 6 ARC headspace longer than the 6 Grendel, it could still chamber, but the bolt would not lock up properly, and in a poorly functioning rifle system, that could result in an out of battery discharge - which is a devastating failure.

I don't think the potential case of a handloader taking their 6mm Grendel handloads and attempting to fire them in a 6 ARC rifle (creating a potential out-of-battery discharge) is a reasonable safety concern for any company. That is squarely in the personal responsibility category when you are fabricating your own non-standardized ammunition. It's a use case that doesn't involve both factory rifle systems and ammunition combinations, which would be cause for liability.

How is the 6 ARC any less safe than for any other factory cartridge offering?

 

[dcali]

I think the way Hornady made it headspace shorter is safer than if they made it longer:

If somebody takes 6mm ARC factory ammunition and tries to fire it in a 6mm Grendel rifle (a reasonable possibility for someone ignorant) - it chambers fine, the bolt can close and lock up properly - helping prevent an out-of-battery discharge - and it may or may not fire due to the probable light primer strike. If it fires, you get case stretch and at worst the case ruptures, gas is diverted back through the action and leaves part of the case in the chamber as the case head is extracted. Most of the time this should result in no injury to the shooter, as most rifle systems are designed to safely handle this kind of case failure.

If Hornady made the 6 ARC headspace longer than the 6 Grendel, it could still chamber, but the bolt would not lock up properly, and in a poorly functioning rifle system, that could result in an out of battery discharge - which is a devastating failure.

I don't think the potential case of a handloader taking their 6mm Grendel handloads and attempting to fire them in a 6 ARC rifle (creating a potential out-of-battery discharge) is a reasonable safety concern for any company. That is squarely in the personal responsibility category when you are fabricating your own non-standardized ammunition. It's a use case that doesn't involve both factory rifle systems and ammunition combinations, which would be cause for liability.

How is the 6 ARC any less safe than for any other factory cartridge offering?

It's more a matter of having to have this discussion at all. If the cartridges are so similar that you even have to think about this, then you can probably just use the older cartridge. I'm all for innovation though. If it catches on, great. the mid-sized 6mm market is getting REALLY crowded though...

 

[SG4247]

The 6ARC cartridge will chamber in probably every one of the 2 million 6.5 Grendels already out there.

Hopefully, only the accuracy will suffer.