New 6mm Advanced Rifle Cartridge

[Gtscotty]

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.

 

[Varminterror]

A fantastic addition to the line up of standardized AR cartridges. I had lusted after a 6mm Grendel variant a few years before finally building my 243 LBC. Admittedly, the 243 LBC, like the doppelgänger 6mmAR produces rather milquetoast results compared to some of the other variants like the Turbo40 or Grinch, but very impressive downrange for an AR nonetheless. The shorter ARC seems to give up even further performance below the 243LBC/6mmAR, but still very useful for the AR-15.

When this reaches critical market mass for availability, I’ll be quite pleased to buy one in a 16” bolt gun, and will recommend it highly as the best factory option for deer hunting.

 

[LoonWulf]

I was thinking it would make a really neat round for what i do....course i think EVERY round makes a neat round for what I do.

I'm curious as to why they shortened it.

 

[troy fairweather]

Can't find much info yet, guess it's for guys not wanting to fireform. I've been wanting a 6mm for my 700 but this won't work.

 

[adcoch1]

I will wait to see what real world ammo velocities are, but a 6mm grendel variant should be awesome in a standard form. Otherwise I will probably try one of the wildcat versions. I own ZERO 6mm stuff though, so not in a huge hurry. Although I do have a set of dies for this 6mm wildcat....

 

[Varminterror]

Can't find much info yet, guess it's for guys not wanting to fireform. I've been wanting a 6mm for my 700 but this won't work.

There’s no fireforming for 243LBC or 6mmAR. Straight neck down.

I would propose, instead, it is to make use of longer, high BC, heavyweight, long ogive bullets while still fitting within a 2.26” magazine and without committing the base of the bullet below, or at least as far below, the shoulder junction. That’s a limiting factor for the 243LBC and 6mmAR, as pictured below with a 105 Hybrid seated to mag length in a 243LBC. I’m about out of bearing length left before my ogive slips into the case mouth.

 

[troy fairweather]

There’s no fireforming for 243LBC or 6mmAR. Straight neck down.

I would propose, instead, it is to make use of longer, high BC, heavyweight, long ogive bullets while still fitting within a 2.26” magazine and without committing the base of the bullet below, or at least as far below, the shoulder junction. That’s a limiting factor for the 243LBC and 6mmAR, as pictured below with a 105 Hybrid seated to mag length in a 243LBC. I’m about out of bearing length left before my ogive slips into the case mouth.

View attachment 898942

What's the expected barrel life for these smaller 6mm, I know there are to many variables to list but a rough number would be nice. I am looking for a 6mm.470~ rim case for my 700 but. Have to decide on barrel life of speed.

 

[bangswitch]

How does this new 6mm ARC compare to the 6.5G past 750 yards? Past 1000 yards? Is the lighter bullet moving faster better in crosswind? Or is this new round designed more for shorter ranges? Seems it would have the same shortcomings next to the 6.5G as the 6.5G has next to the 6.5 Creedmoor.

 

[Gtscotty]

I was thinking it would make a really neat round for what i do....course i think EVERY round makes a neat round for what I do.

I'm curious as to why they shortened it.

I'm sure as Varminterror noted, the intent was to shorten the case to better handle long 6mm bullets (108gr ELD?) at AR mag length. From the cut sheet, not only did they push the shoulder back 0.03", but they kept the same shoulder diameter as the Grendel, resulting in more case taper for the 6mm ARC than for the 6.5 Grendel or 6mm AR. Not sure why they did that, but the larger case taper also costs some capacity.

How does this new 6mm ARC compare to the 6.5G past 750 yards? Past 1000 yards? Is the lighter bullet moving faster better in crosswind? Or is this new round designed more for shorter ranges? Seems it would have the same shortcomings next to the 6.5G as the 6.5G has next to the 6.5 Creedmoor.

It will be throwing a lighter bullet with an equivalent BC faster than the 6.5 G, so the exterior ballistics should be better. The 6.5 G vs 6.5 CM is a totally different situation, the CM can throw bullets with much higher BCs faster than the G, or it can throw the same bullets as the G several hundred fps faster, apples and oranges.

 

[Varminterror]

What's the expected barrel life for these smaller 6mm, I know there are to many variables to list but a rough number would be nice. I am looking for a 6mm.470~ rim case for my 700 but. Have to decide on barrel life of speed.

I haven’t burned out my 243LBC yet, but based on 6 BR and Dasher experience, I’m hoping for 2,800-3,000 rounds from mine before it won’t hold up for PRS matches. I do expect it may give up earlier than that, since I have heard a lot of folks talk about 2500-2800 from 6 PPC’s, which are smaller still, but I’ll be happy with anything over 2500, considering my 6 creeds don’t make it past 1500. For moderate range hunting and plinking, it would go much, much farther before it lost sufficient accuracy.

How does this new 6mm ARC compare to the 6.5G past 750 yards? Past 1000 yards? Is the lighter bullet moving faster better in crosswind? Or is this new round designed more for shorter ranges? Seems it would have the same shortcomings next to the 6.5G as the 6.5G has next to the 6.5 Creedmoor.

This will shoot flatter with less wind drift than the 6.5 Grendel. I can push a 105 Hybrid to 2900 from a 24” barrel with the 243LBC, looks like this smaller case won’t run as fast, but it’ll run ~200fps faster with a 105 than the 6.5 Grendel runs with a 123grn bullet - reminding the 105 has a .536G1, vs. only .506G1 of the 123 ELD-m. Faster AND more aerodynamic.

This will have a longer super-sonic range, making the 1000-1200yrd shots simpler with this than the 6.5 Grendel. The same effect happens with the 6 creed and the 6.5 creed. Any given rifle match, when I compare data cards with the 6.5 guys, I will generally have 2-4 tenths less drop and 1-3 tenths less windage with my 6 creed. There tends to be at least one target at every match where those guys are running around with their kestrels checking wind, talking about their wind brackets and how they want to hold, because their wind estimation error bracket is wider than the target... but mine isn’t... which is one of the two major reasons I tolerate my barrels going down 1,000 rounds earlier than theirs, it’s effectively the only way to “buy points” in PRS - shoot a 6 instead of a 6.5.

The comparison between the 6.5 creed and 6.5 Grendel isn’t apt for the 6.5 Grendel vs. 6mm ARC and other 6mm Grendel variants. The 6.5 Creed pushes a 140 with a BC of .618G1 about 200fps faster than the 6.5 Grendel pushes the 123’s, again, with a .506G1. Both the 6.5 creed and the 6mm ARC run higher BC bullets at faster speeds than the 6.5 Grendel - so both stand taller as better performers. The 6mm ARC should have a trajectory more similar to a 6.5 creed than the 6.5 Grendel, but using ~25% less powder, and about a 30% reduction in recoil. It won’t hit nearly as hard at 1,000, but it’ll get there with similar windage and similar drop as 6.5 creed (and less than 6.5 Grendel).

 

[troy fairweather]

I haven’t burned out my 243LBC yet, but based on 6 BR and Dasher experience, I’m hoping for 2,800-3,000 rounds from mine before it won’t hold up for PRS matches. I do expect it may give up earlier than that, since I have heard a lot of folks talk about 2500-2800 from 6 PPC’s, which are smaller still, but I’ll be happy with anything over 2500, considering my 6 creeds don’t make it past 1500. For moderate range hunting and plinking, it would go much, much farther before it lost sufficient accuracy.



Ok thanks that's pretty good barrel life, I have a idea id like to try but just my be stupid. I'd like to chamber a sporter weight barrel in some 6mm target round, from my ss700, I have a nice old Remington walnut adl stock to use. Or a composite bdl with the bottom medal, Hurd 6br sometimes does not feed proper so a case with more body like the dasher maybe better.

This will shoot flatter with less wind drift than the 6.5 Grendel. I can push a 105 Hybrid to 2900 from a 24” barrel with the 243LBC, looks like this smaller case won’t run as fast, but it’ll run ~200fps faster with a 105 than the 6.5 Grendel runs with a 123grn bullet - reminding the 105 has a .536G1, vs. only .506G1 of the 123 ELD-m. Faster AND more aerodynamic.

This will have a longer super-sonic range, making the 1000-1200yrd shots simpler with this than the 6.5 Grendel. The same effect happens with the 6 creed and the 6.5 creed. Any given rifle match, when I compare data cards with the 6.5 guys, I will generally have 2-4 tenths less drop and 1-3 tenths less windage with my 6 creed. There tends to be at least one target at every match where those guys are running around with their kestrels checking wind, talking about their wind brackets and how they want to hold, because their wind estimation error bracket is wider than the target... but mine isn’t... which is one of the two major reasons I tolerate my barrels going down 1,000 rounds earlier than theirs, it’s effectively the only way to “buy points” in PRS - shoot a 6 instead of a 6.5.

The comparison between the 6.5 creed and 6.5 Grendel isn’t apt for the 6.5 Grendel vs. 6mm ARC and other 6mm Grendel variants. The 6.5 Creed pushes a 140 with a BC of .618G1 about 200fps faster than the 6.5 Grendel pushes the 123’s, again, with a .506G1. Both the 6.5 creed and the 6mm ARC run higher BC bullets at faster speeds than the 6.5 Grendel - so both stand taller as better performers. The 6mm ARC should have a trajectory more similar to a 6.5 creed than the 6.5 Grendel, but using ~25% less powder, and about a 30% reduction in recoil. It won’t hit nearly as hard at 1,000, but it’ll get there with similar windage and similar drop as 6.5 creed (and less than 6.5 Grendel).

 

[Varminterror]

@troy fairweather - assuming you have a .473” boltface 700, I would build a 6mm Dasher instead of this new cartridge. Not necessarily because the Dasher is substantially better (largely is), but because it will be substantially easier. It’ll feed from the ADL or BDL mag boxes you have, and work in the .473” boltface you already have. Multiple sources offer 6 Dasher brass and dies, and Lapua offers 6 BR brass which is easily fireformed to Dasher (I use a false shoulder with nearly standard loads) - and both will use ~30grn of Varget or 8208, 30-35ish for the Dasher, 25-30 for this 6 ARC. Very similar barrel life, but ~200fps faster for the Dasher.

In an AR, this ARC makes more sense, but in a 700, the Dasher makes more sense to me.

I’ll admit, I’m excited about the prospect of a factory offered CZ 527 Varmint Target in 6mm ARC.

 

[bangswitch]

Thanks, Varminterror, that info is what I was looking for. >Sigh<, looks like I'll have to build another AR, lol.

I really like my AR Grendel, and have stretched it to 1125 yards. My loads ballistic data calculate them going subsonic at 1175-1200. I'll have to live with that, I'm not going to chase another couple hundred yards. If another rifle is in my future, it will be a Creedmoor. Maybe a 6mm?

 

[adcoch1]

I’ll admit, I’m excited about the prospect of a factory offered CZ 527 Varmint Target in 6mm ARC.

My exact thoughts...

 

[ECVMatt]

I have to admit that I was initially excited, but a .243 @ 2700 doesn't do much for me. I would rather just have a regular BA .243 @ 3100 or so and not sweat the ballistics so much. I will admit that I am old school and prefer a MPB zero to hold overs or Mils. I realize that there is a whole new generation of shooters out there that think the MPB zero is foolish.

I would be excited for an AR that is in between the 15 and the 10; perhaps the mythical 14? It would not suffer the limitation of either system, yet take advantage of both.

However I am glad to see that the search for Excalibur continues!

 

[troy fairweather]

Ya it's a .473 bolt, a cz in the new round would be cool. Thanks for the info.

 

[js8588]

This makes me inappropriately happy...

 

[Varminterror]

If another rifle is in my future, it will be a Creedmoor. Maybe a 6mm?

I bought a 6.5 Creed shortly after it dropped, just for the sake of trying and for hunting. For long range shooting, I found it milquetoast, such I replaced it with a 6 creed. I have 3 now, and plan to always keep one in the stable, replacing the 243win’s and AI’s I had kept before. I like the 6 creed a lot.

 

[Varminterror]

I have to admit that I was initially excited, but a .243 @ 2700 doesn't do much for me. I would rather just have a regular BA .243 @ 3100 or so and not sweat the ballistics so much.

That performance simply isn’t possible from an AR-15, or other 2.3” action.

I will admit that I am old school and prefer a MPB zero to hold overs or Mils. I realize that there is a whole new generation of shooters out there that think the MPB zero is foolish.

Methinks you’re missing the point, as your criticism of the cartridge contradicts your stated reason for criticizing it. This type of cartridge improvement extends the MPBR of the AR-15.

You’re also hanging your hat on a 23 yard difference in MPBR (5”).

If you simply prefer to run a bolt action, especially one which eats ~30% more powder and carries 20% more recoil to do the same job in the field, with less than half of the barrel life, and you really want to stand up on 23 extra yards of MPBR, then assuredly, nobody will force you to buy anything new.

 

[mshootnit]

Looks like SAAMI pressure will be limited to 52,000 psi which is in line with older observations of about 50,000 psi max for 6mm PPC in AR actions to prevent bolt lug damage.
However in a bolt gun , pressures closer to 65,000 could potentially be utilized enhancing performance of the round.

 

[Varminterror]

52kspi is the SAAMI standard for 6.5 Grendel, parent case for the 6 ARC, simple carry over. Bolt thrust is bolt thrust; pressure x head area, it doesn’t care which caliber.

I’m not certain a guy can get enough slow burning powder into a Grendel case - especially this slightly downsized version - to really push pressures. Most of my top end Grendel loads have been compressed already, translating the same to 243LBC. I know I can’t get enough 8208 into the case, I’m already running on the ragged edge of springing bullets back out of the cases - which I suppose is one way to spike pressure, run a compressed charge which inadvertently pushes your bullet out into the lands.

 

[Llama Bob]

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

 

[Gtscotty]

I’m not certain a guy can get enough slow burning powder into a Grendel case - especially this slightly downsized version - to really push pressures. Most of my top end Grendel loads have been compressed already, translating the same to 243LBC.

^ This, I've been playing with 8208, AR-Comp and H4895 in my Grendel lately, most loads with longer bullets are crunchy already, I don't know how much you'd really be able to safely run the pressure up with the volumetric constraints of that case. Also, at least in my Starline cases, I'm getting some loose primer pockets in 3 or so firings, some of my load experimentation may run closer to 54ksi - 55ksi, but I think you'd be getting about one firing with that brass at full bolt gun pressures.

 

[Gtscotty]

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

Nosler pushed that exact critter out almost 3 years ago, and hasn't really done anything with it:

https://saami.org/wp-content/uploads/2018/04/24-Nosler.pdf

The pressure is higher, but velocities are still lower.

 

[brasscollector]

They definitely should have done this on the SPC case family

You can get yourself a TAC 6 and have your cake and eat it , unfortunately it is a wildcat.
I've been on the fence about a 6mm AR15 chambering for a while now and this new development isn't going to change a thing. If they designed it off the SPC case I'd be ordering parts right now.

Nosler pushed that exact critter out almost 3 years ago

The Nosler "version" used a 223 bolt face diameter (rebated rim) making the brass expensive and special. I understand some of the reasoning behind that decision but I think it hurt the cartridge more than it helped.