New 6mm Advanced Rifle Cartridge

Gtscotty

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I hadn't seen this posted here yet, but SAAMI 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.
 

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MotorOilMcCall

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I'm with CanSniper... I just bought the AR15Performance 6mmAR barrel, dies, and brass for a new AR build. This is indeed what 6.5G should have been from the start. Wonder how different the case dimensions are...
 

Headquarterz

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I'm with CanSniper... I just bought the AR15Performance 6mmAR barrel, dies, and brass for a new AR build. This is indeed what 6.5G should have been from the start. Wonder how different the case dimensions are...
I haven't looked at it yet. I will say, I had a 6.5g at one point.
It's anemic. Built a 6mm at turbo 40° and now I'm running high bc bullets at slightly less velocity than a 6br. That cartridge is badass.
 

MotorOilMcCall

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Completely agree... I just didn't want to deal with fireforming a bunch of brass... also heard the turbo 40 brass doesn't last more than a few firings, which kind of turned me off to it.
 

Constructor

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From those drawings the shoulder has been pushed back around .020" that will cut powder capacity and velocity . I'll bet most end up buying the normal Grendel necked down to 6mm than that thing and trimming the already available brass.
Lets see who developed it and that will tell us the reason for the changes. Probably be one company making brass and selling ammo and new dies and they will be the only ones to capitalize on it for a while.
Could be Hornady, the guy in charge of making dies bought one of my barrels a few years ago and they make the custom dies I sell. They always said they wouldn't make those dies for anyone else since I had the design and paid for the tooling. Looks like they are just running the reamer in .020" shallow...would be the same to make the dies.
 
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Headquarterz

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From those drawings the shoulder has been pushed back around .020" that will cut powder capacity and velocity . I'll bet most end up buying the normal Grendel necked down to 6mm than that thing and trimming the already available brass.
Lets see who developed it and that will tell us the reason for the changes. Probably be one company making brass and selling ammo and new dies and they will be the only ones to capitalize on it for a while.
Could be Hornady, the guy in charge of making dies bought one of my barrels a few years ago and they make the custom dies I sell. They always said they wouldn't make those dies for anyone else since I had the design and paid for the tooling. Looks like they are just running the reamer in .020" shallow...would be the same to make the dies.
Out of curiosity, aren't you the fella that designed a 6br bolt and make 6br uppers?
 

Constructor

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Out of curiosity, aren't you the fella that designed a 6br bolt and make 6br uppers?
I did make a decent sized production run in 2009 but a patent troll named Kramer applied for a patent about 3 months after I posted a photo of the first bolt on 6mmBR.com in 2007. Several years later they granted him the patent and he threatened to sue me. I can prove I was making the bolts before he filed for the patent but it isn't worth it to me to spend $500 an hour for an attorney to argue my case. Kramer has never made a bolt of any kind...nothing but a troll.
 

Gtscotty

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From those drawings the shoulder has been pushed back around .020" that will cut powder capacity and velocity . I'll bet most end up buying the normal Grendel necked down to 6mm than that thing and trimming the already available brass.
Lets see who developed it and that will tell us the reason for the changes. Probably be one company making brass and selling ammo and new dies and they will be the only ones to capitalize on it for a while.
Could be Hornady, the guy in charge of making dies bought one of my barrels a few years ago and they make the custom dies I sell. They always said they wouldn't make those dies for anyone else since I had the design and paid for the tooling. Looks like they are just running the reamer in .020" shallow...would be the same to make the dies.
I don't know, it will definitely depend on how it's rolled out and by which company. If it's a small outfit and done without much industry buy-in or support, there won't be much reason to get it over the 6mmAR. If it's a Hornady style rollout, with lots of components, load data and good factory ammunition, I can see it overtaking the various similar wildcats for most shooters overnight. Easy and well established are compelling traits for lots of folks, not everyone wants to put in the effort messing with wildcats. It will be interesting to see what happens.

i am curious how much capacity this case will give up to the 6mmAR? The shoulder is pushed back about 0.03", but still shares the Grendel shoulder diameter, resulting in more case taper than a regular Grendel. It doesn't seem like the case could give up more than a few grains of capacity and still hit the published velocity at 52ksi MAP though.
 
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Gtscotty

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Same as a 6mmAR. 243LBC, 6mm Predator, 6 WOA, 6-6.8 shot out of 20" barrels but I'm betting that figure is using a 24" barrel and Hornady factory loads.
Do you think Hornady is probably the company behind the SAAMI listing? Rather, I guess, have you heard through the grapevine who's behind it?
 
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MotorOilMcCall

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Wonder if we'll be able to use that brass with Constructor's barrels (may fire form the shoulder out a bit). I've spent the past few hours necking down a couple hundred Hornady 6.5G cases.
 
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MotorOilMcCall

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All depends on what you want to do with it. If you intend on using it for anything other than target shooting, the 6mm packs a heck of a lot more energy. Some states don't allow game hunting with a 22 cal either, where as the 6mm is allowable.
 

Milemarker28

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Just when I’m close to pulling the trigger on ordering a 12.5” grendel barrel this drops. Now I have to wait and see what support this gets and who wants to be the first to try it out in a short barrel configuration.
 

Baron85

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For a sbr why not the 6.8? I have a 12.5 6.8 and love it. Figured it was better suited for the short barrels and the Grendel for the long barrels????
 
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cleric

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That’s the general saying but there is not a big difference in 6.8 and grendel sbr performance. So if you have a longer grendel makes supply chain easier.
 
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sam4886

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Shit, throw a grendel barrel in your SBR and shoot it. When you can finally get parts for this thing in a year or two order a new barrel. Everything else will be the same.

I'm hoping that ARP stuff will work as well. Forming the brass for my 6mm predator isn't bad at all, but full commercial support is never a bad thing. More load info, baby.
 

Gtscotty

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Why would you want a 12.5" Grendel? Kind of waste's the whole point of the round doesn't it?
The 6.5 Grendel is a good mid-range intermediate cartridge, but it's not really a great long range cartridge in the grand scheme of things. Why saddle a rifle down with a long, heavy barrel just to get slightly less ho-hum long range ballistics when you could have a compact handy package with good short and medium range performance? For a real, heavier long range package, something with better external ballistics like the 6mm AR or even stepping up to a larger platform with the 6 or 6.5 CM makes more sense to me.

The 6.5 G and 6.8 SPC are very, very, very similar if one's good for something, the other is going to be fairly decent as well.
 

Yondering

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Why would you want a 12.5" Grendel? Kind of waste's the whole point of the round doesn't it?
Not at all; the Grendel is a great cartridge in a 12.5" barrel. The 6.8 fans like to push that line about the Grendel only being good in long barrels, but it's not true.

In my personal experience, my 12.5" 6.5 Grendel is considerably easier to hit with at 600+ yards than my 16" 5.56 if there is any wind at all. It also hits significantly harder at that distance. It's not truly a long range round in the sense of 1,000+ yards, but in a 12.5" barrel it is capable from room clearing distance to well over 600 yards.

Also, there are some very good bullet options for a short barrel 6.5 Grendel for both long range ballistics and hunting, the 129gr ABLR being the top choice IMO.

As much as I like the 6mm Grendel family of cartridges, IMO for a 12.5" I would choose the larger 6.5mm bore.
 

Constructor

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To echos @cleric point, there isn’t much of a difference but my hope is that the 6ARC can possibly offer a little more speed in a sbr configuration.
I haven't gone as short as a 12.5 but really like the 95SMks in an 18" TAC6 at 2800fps. I had 4000 custom solid copper bullets made same shape as the 95SMK. Barnes 85TSX performs well too.
 

Constructor

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For a sbr why not the 6.8? I have a 12.5 6.8 and love it. Figured it was better suited for the short barrels and the Grendel for the long barrels????
With handloads you can get 150-200fps more out of the 6.8 than you can with max handloads in the Grendel. Hornady factory 6.8 loads run 80-100fps faster than their Grendel loads with the same weight bullets and barrels of the same length.
 
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hlee

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How do velocities compare between the 6.5G and the 6.8 SPC when comparing bullets of the same BC?
 

ed308

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I haven't heard that. Maybe with this cartridge being introduced they'll release their version. ARP's 6mm Tac6 which is based on the 6.8 case and bolt is a nice cartridge. Had one for a year but decided one wildcat (270AR) was enough.
 

Constructor

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How do velocities compare between the 6.5G and the 6.8 SPC when comparing bullets of the same BC?
About the same, the 6.8 will shoot a 130 Berger about the same velocity as the Grendel can shoot a 123 at max SAAMI operating pressure. The owner of Cavity Back bullets was getting crazy speeds out of the hand loaded 130 Bergers.
 
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Crews

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I looove me some 12.5” 6.5 & 6.8 SBR’s for hunting, always figured a 6mm might do it better. Sure hope someone makes an option with factory ammo available soon!
 

Constructor

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Taken off of AR15performance. I’ve been tempted a few times by a 6mmAR. Once this thing has good availability I’ll have to get one going.
At the moment Hornady will not admit they are going to do it. There are no gauges, dies, brass or ammo. I could have a batch of barrels in 60 days but I'm not going to produce barrels until all the other parts are out there.
 

Ledzep

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    Federal missed the boat on this. Should've made a 6mm Valkyrie with the 6.8 case and bolt.
    I think the Grendel case is a better base for these type of cartridges, IMO. If the basis is to shoot long ogive heavy for caliber low drag bullets, the shorter, (slightly) fatter case is much more forgiving. The 224 Valkyrie already suffers from having too much bullet stuffed into the case. If they kept the same case length you couldn't seat several of the 105-115gr options and stay in AR-15 mag length. Even if you could you're right on the edge with most of the bullet stuffed into the case.
     
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    Constructor

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    I think the Grendel case is a better base for these type of cartridges, IMO. If the basis is to shoot long ogive heavy for caliber low drag bullets, the shorter, (slightly) fatter case is much more forgiving. The 224 Valkyrie already suffers from having too much bullet stuffed into the case. If they kept the same case length you couldn't seat several of the 105-115gr options and stay in AR-15 mag length. Even if you could you're right on the edge with most of the bullet stuffed into the case.
    I make a TAC6, it is a 6mm Herrett for all practical purposes. Because we can run pressures up to 60,000psi in the 6.8 cases and the bolts are stronger we can match the velocity of the 6mms based on the Grendel case and accuracy is very good.
    5.56 bolts have a 3:1 safety margin meaning they were designed to handle 3 times more thrust than a 5.56 can generate. When you go to the Grendel it is running near a 1:1 because the rim that the lugs attach to is so thin there is only 50% strength on a .136 length of the lugs. The lugs are .277" long -.136 =.141 so apx half of each lug has 100% strength and half of each lug(forward most) has 50% strength. That is why it looks like the lugs have been ripped off a failed bolt.
    I agree to a point the Valkyrie could have been done better to save some powder capacity. I blew out the shoulder diameter and have it .050 further forward with a slightly shorter neck so my TAC 6 and TAC 30 have more powder capacity and the cases are shorter.