6mm ARC vs 6mm Max

[TheVolunteers]

Hey all, been awhile since I've posted here and hoping to get the Hide's advice on an upper build I am looking at pursuing. I currently have a 16" 223 Wylde build that is my do all rifle based on a Seekins lower with LMT SOPMOD stock, Spikes T2 buffer, Tubbs flat wire spring, and Geissele SSA-E trigger. I'm looking to build two additional uppers, one in a 300blk for CQB work, and a 6mm offering as a DMR type platform to reach out to the 1000m territory and possibly use in PRS competition.

For the DMR build precision and reliability are my top priority, which has me in the pickle over 6mm ARC vs 6mm Max. I've read a lot about both cartridges here and elsewhere, and while 6mm ARC has more history and development, I'm concerned about some of the things I've read about reliability. Magazine feeding (although it sounds like that's been getting better with newer designs) and bolt lug/extractor failures. I've also read about the 6 ARC running excessively dirty particularly when suppressed, which I am planning on running a suppressor for this build (probably a flow through design that would hopefully mitigate some of dirtiness). That being said, 6 ARC sounds like it handles the heavier projectiles better that would be suited for long range work (I'm thinking about 20-22" barrel for what it's worth).

Now onto 6mm Max, I like the idea that on paper it sounds more reliable using a standard 223/5.56 bolt face. But I know it still requires proprietary magazines, and there's been very little development/literature out on the cartridge. I know it also won't handle some of the larger projectiles over 105 grain.

So should I try the new kid on the block that might fizzle out completely (6mm Max), or go for the more tested but possibly more finicky 6 ARC? I do reload so factory ammo availability isn't as much of a concern for me. I appreciate any guidance you guys have!

 

[lonestar1845]

Having both, if your goal is to try to make a PRS rifle out of an ar-15, I'd go 6 ARC. It was built for the heavier bullets. It's accurate and slow.

The 6 max is more diverse. It really shines with the lighter bullets in short barrel rifles and the 90 grain in standard length barrels. It can run the 105's, but it's stuck pretty far into the case. If building a fighting or hunting rifle, I'd pick 6 max.

 

[ut755ln]

Having both, if your goal is to try to make a PRS rifle out of an ar-15, I'd go 6 ARC. It was built for the heavier bullets. It's accurate and slow.

The 6 max is more diverse. It really shines with the lighter bullets in short barrel rifles and the 90 grain in standard length barrels. It can run the 105's, but it's stuck pretty far into the case. If building a fighting or hunting rifle, I'd pick 6 max.

What he said.

Also, the Geissele magazines are fantastic for the 6ARC but expensive. I have not had bolt face issues but I also do not have a high round count yet.

 

[vmpglenn]

I've been shooting 6.5 Grendel (big brother to 6ARC) for decades and just got into 6Max. I'm a fan of 6Max and find it really matches my shooting needs out to 600 yards (max distance at my range).

I've shot it with 90gr factory loads, 100gr and 103gr handloads. The 100s go 2600 out of a 14.5" barrel, recoil is much lighter than Grendel, suppresses really well, feeds reliably from 20rd 350 Legend AR mags, and even works really well in my LWRCi Six8 receiver set using the Magpul Six8 magazines. Accuracy with my SOLGW barrel has been very good, consistently 1" - 1.5" 5rd groups at 100. If the round hangs on it'll be my go-to in the AR15 for sure.

 

[Rob01]

Having both, if your goal is to try to make a PRS rifle out of an ar-15, I'd go 6 ARC. It was built for the heavier bullets. It's accurate and slow.

The 6 max is more diverse. It really shines with the lighter bullets in short barrel rifles and the 90 grain in standard length barrels. It can run the 105's, but it's stuck pretty far into the case. If building a fighting or hunting rifle, I'd pick 6 max.

More diverse? Lol Not the dems here. The ARC can shoot light bullets too. Why would you limit yourself with a cartridge that can do one thing but not both? Why if building a “fighting or hunting rifle” would you go with the Max?

 

[vmpglenn]

More diverse? Lol Not the dems here. The ARC can shoot light bullets too. Why would you limit yourself with a cartridge that can do one thing but not both? Why if building a “fighting or hunting rifle” would you go with the Max?

For me, it's the ability to use the 5.56 bolt, reliable feeding out of readily available mags, and very efficient use of powder. My range is limited to 600 yards so there's that.

 

[Rob01]

For me, it's the ability to use the 5.56 bolt, reliable feeding out of readily available mags, and very efficient use of powder. My range is limited to 600 yards so there's that.

Using the 5.56 bolt is nice. So the max uses 5.56/.223 mags?

 

[Hecouldgoalltheway]

I've been shooting arc since the first barrels were made and I've never broken a bolt face. Don't buy cheap shit. Nobody has ever broken a quality bolt face on an arc without doing something really stupid with it. If you buy acme parts, you should expect shit to break. The accuracy is unreal, from 55gr to 109gr, it shoots everything remarkably well. I've assembled a half dozen of theses rifles with different barrels on each one, and they were all sub moa with anything hornady has put out. With handloads? You wouldn't believe me. I've been through a handful of magazine manufacturers, and I've never had a single feeding issue. I've got 7rd, 10rd, 12rd, and 25rs mags from at least 4 different manufacturers, and I've shot probably 5k rounds without ever having a single malfunction. The strange "issues" with the 6arc seem to have never appeared on my rifle, nor any of the half dozen of my hunting buddies that shoot it either. The max does less, and solves problems that don't exist. You can keep it.

 

[TheVolunteers]

All great information, thanks for the feedback. For those of you running the 6 ARC, have you run it suppressed and have you been able to mitigate some of the excessive blowback/dirtiness? I know getting the gas tube length correct is the first major step, and I'm planning on running an adjustable gas block as well as flow through can, so hoping these features could lend the build to be tuned so that it runs fairly clean?

 

[Hecouldgoalltheway]

All great information, thanks for the feedback. For those of you running the 6 ARC, have you run it suppressed and have you been able to mitigate some of the excessive blowback/dirtiness? I know getting the gas tube length correct is the first major step, and I'm planning on running an adjustable gas block as well as flow through can, so hoping these features could lend the build to be tuned so that it runs fairly clean?

Again, a non-isue. I've fired almost every round with a can, and so have my buddies. SA bleed-off seems to be the best I've used, whether an arc or any other gas gun. Adjustable gas blocks, correct gas length on the barrel, and you'll be fine. The real issue is, (I think), that it shoots so well over leverevolution, and that stuff is one step away from black powder in cleanliness. With almost any other powder, it isn't any worse than any other ar cartridge I've used.

 

[wade2big]

@Hecouldgoalltheway, which bolts do you use? Only 6arc I have is a Seekins but plan on putting a 16” together.

 

[Hecouldgoalltheway]

@Hecouldgoalltheway, which bolts do you use? Only 6arc I have is a Seekins but plan on putting a 16” together.

JP. They made them right out of the gate. I actually bought a spare years ago for my primary rifle, (and it has become my primary rifle, stays in my truck, kills coyotes and whitetail like magic), and it's still in it's original box. Over 5k rounds on the one in my rifle, and never an issue. When I clean it, it looks like it's brand new..

 

[lonestar1845]

More diverse? Lol Not the dems here. The ARC can shoot light bullets too. Why would you limit yourself with a cartridge that can do one thing but not both? Why if building a “fighting or hunting rifle” would you go with the Max?

Perhaps I should have picked a better word, lol. I haven't had the best luck reliably running light bullets with the ARC, especially without a can on. The max runs everything great with the same setup and great accuracy. So I'd argue that the max is the cartridge that does both things well and the other not so much.

Why do I pick the Max over the ARC for a fighting or hunting rifle?

1. Reliability. There's a reason everyone is trying to make stronger bolts and proprietary feed ramps for the ARC. Even the factory loads offer little wiggle room with pressure. Add in some dirt/ mud/ water to the chamber and bore and that pressure goes up.

2. Velocity. The Max handles the lighter bullets better. In an AR-15 platform, I'm more interested in 600 yards and in. I kill alot of critters, and a 70 grn. @3300 FPS and a 90 grn. @2900 FPS dumps them better than a 108 at 2600 FPS.

3. Mags that fit in mag pouches I already have. Unless you want to buy the $120 Geissele mag.

 

[45-90]

So the 6 mm max has 35.0 gr of H2O capacity, and I just weighed a 6mm ARC Starline grendel converted case, it also has 35 gr of H2O capacity.
Exactly the same capacity.
Hornady manual has 18" auto ARC 90 gr at 2850 fps the same velocity as reported by the guy shooting the 6 max, and says his factory ammo is $1.50 per shot.
Stands to reason same capacity, same velocity.
But the 6mm ARC will handle heavier bullets with much higher BC, and still fit the magazine, which is what it was designed for.
Heavy match bullets with much higher BCs are much better in the wind than 90 gr bullets. The wind is much more difficult than trajectory.
My vote is for the 6mm ARC it suits my needs, better with 107, & 108, gr bullets.
Two cases with the same capacity, just configured differently.
So if run in same barrels lengths at the same pressures velocities will be very close to the same.
And 52 vs 55 thousand psi ain't gonna make much difference either for gas guns, not to be confused with bolt guns.
Just the facts,... your choice.
But others have been used in the past like neck up 22 Nosler to 6mm, or 6mm Hagar with 37.3 gr H20 for more light bullet velocity...or single load heavy bullets.
Plus a host of other wildcats, so Nothing new here.

 

[Hecouldgoalltheway]

With a quick look at ammoseek.com you'll see that almost all factory 6arc options are available for less than $1.25/ round.

I searched 6 max, and it laughed at me. Not an option. The 6mm arc factory ammo is so good that you cannot justify loading for it for what it costs. It's all sub-moa in every rifle I've tested.

So, if you want to handload exclusively for a cartridge with less capability, to avoid problems brought on by using garbage parts in your rifle, sounds like the 6 max is for you.

 

[SFree]

With a quick look at ammoseek.com you'll see that almost all factory 6arc options are available for less than $1.25/ round.

I searched 6 max, and it laughed at me. Not an option. The 6mm arc factory ammo is so good that you cannot justify loading for it for what it costs. It's all sub-moa in every rifle I've tested.

So, if you want to handload exclusively for a cartridge with less capability, to avoid problems brought on by using garbage parts in your rifle, sounds like the 6 max is for you.

How does the 6ARC run, full auto, or sustained rates of fire over time? Is it capable of being a fighting rifle or just the occasional plinking rifle? I’m truly not being snarky, but am curious as to it’s potential as I have no experience with it…

 

[ut755ln]

All great information, thanks for the feedback. For those of you running the 6 ARC, have you run it suppressed and have you been able to mitigate some of the excessive blowback/dirtiness? I know getting the gas tube length correct is the first major step, and I'm planning on running an adjustable gas block as well as flow through can, so hoping these features could lend the build to be tuned so that it runs fairly clean?

Mine are not gassier or dirtier than any other rifle I have similarly setup.

 

[WindstormSCR]

How does the 6ARC run, full auto, or sustained rates of fire over time? Is it capable of being a fighting rifle or just the occasional plinking rifle? I’m truly not being snarky, but am curious as to it’s potential as I have no experience with it…

Guy with an 07/02 locally has run a 6Arc upper on one of his MG lowers and as far as he's told me when I inquired he said he's not had any malfunctions or stoppages, or any of the other 6Arc issues.

He's using a JP bolt, Custom cut barrel on I believe a Criterion blank, and Geissele GFR magazines. Barrel length 14.5", Flow 6k Suppressor

one thing he did do was contour the barrel for a JP thermal dissipator sleeve, and the whole point of the exercise was to see if it improved accuracy after high fire rates, and it seems to do so.


I've said in other threads that the 6 Max is interesting to me mostly because it should work in M27 links for things like the Shrike upper

 

[Hecouldgoalltheway]

How does the 6ARC run, full auto, or sustained rates of fire over time? Is it capable of being a fighting rifle or just the occasional plinking rifle? I’m truly not being snarky, but am curious as to it’s potential as I have no experience with it…

I have no idea, but it was developed for military use in such a capacity, so I'd imagine it handles just fine. I can't imagine why the answer to that question matters though. If you believe you'll be mowing down waves of chicoms with your AR in a red dawn style invasion, you should spend $10k on a kak setup. I hear they are very popular with larpers.

 

[45-90]

The 6mm ARC was considered in 2022 by the DOD and Hornady submitted for testing . Go look at Hornady’s old advertisements and articles in Guns and Ammo mag as the 6mm ARC was considered.
But the DOD already made the decision since 2022, and went with the XM5, AND XM250 for their new rifles to replace some of the M4s and 249 SAW.

It's 6.8 or .277 dia, 135 gr armor piercing bullet, at 3000 fps from 13" barrel, to penetrate Russian body armor. In a hybrid case to contain the high pressure round...complete with suppressor. Electronic range finding optics, with auto range available, on these new high velocity high BC rounds.
I saw a cute blonde female reporter, on video, who never shot a rifle, hit the target at 1200 yds just following the military instructors instructions, with these optics.
So I don't think the DOD is interested in the 6 Max and 90 gr bullets.
I'd choose the 5.56 and 77 grs I already have that, and it works.

 

[WindstormSCR]

The 6mm ARC was considered in 2022 by the DOD and Hornady submitted for testing . Go look at Hornady’s old advertisements and articles in Guns and Ammo mag as the 6mm ARC was considered.
But the DOD already made the decision since 2022, and went with the XM5, AND XM250 for their new rifles to replace some of the M4s and 249 SAW.

It's 6.8 or .277 dia, 135 gr armor piercing bullet, at 3000 fps from 13" barrel, to penetrate Russian body armor. In a hybrid case to contain the high pressure round...complete with suppressor. Electronic range finding optics, with auto range available, on these new high velocity high BC rounds.
I saw a cute blonde female reporter, on video, who never shot a rifle, hit the target at 1200 yds just following the military instructors instructions, with these optics.
So I don't think the DOD is interested in the 6 Max and 90 gr bullets.
I'd choose the 5.56 and 77 grs I already have that, and it works.

The 6Arc was never for the NGSW program.

Tangent: Your premise about the NGSW being to penetrate Russian body armor is also false, the documents available clearly state a concern regarding the ability of anti-fragmentation soft armor from even non-peer forces to defeat 855A1 past as little as 250m

6 Arc was developed for the cool kids club (JSOC + Three Letter Agencies) who wanted something better than 5.56 but needed it to fit in existing platforms, who aren’t in the business of fighting full scale wars but are instead usually black bagging some poor fuck.

I can see 6 Max potentially being of interest to the USMC down the road as an upgrade to the M27 IAR, depending on what bullets end up being cooked up for it

 

[Bart]

As far as 6 arc suppression, I have had great luck with the rubber city armory adjustable bolt carrier, if that helps...

 

[45-90]

I doubt any armed forces would be interested in 6 max....the new round already selected is 6.8X 51.
I would use the 5.56 as my personal civilian close range weapon...cause I have it and it works, ammo is available everywhere, no reason for me to own a 6 max, but those who want one, should get one.
Plus I already have a 6 ARC with the same powder capacity, and more versatile for my personal needs.
I'm not gonna face off against a Russian or Chinese army with it or with anything else including the 6 mm max....that would be suicide.
But MAC V SOG used the car 15 with great success, behind energy lines. Plus a bunch of other calibers like 9mm submachine guns, 22LR, 45ACP, 38 Special, rocket pistol, 444 Marlin, bow and arrow, were also tried... The hammer was air support, regardless of which small arms were used.

 

[Hecouldgoalltheway]

I doubt any armed forces would be interested in 6 max....the new round already selected is 6.8X 51.
I would use the 5.56 as my personal civilian close range weapon...cause I have it and it works, ammo is available everywhere, no reason for me to own a 6 max, but those who want one, should get one.
Plus I already have a 6 ARC with the same powder capacity, and more versatile for my personal needs.
I'm not gonna face off against a Russian or Chinese army with it or with anything else including the 6 mm max....that would be suicide.
But MAC V SOG used the car 15 with great success, behind energy lines. Plus a bunch of other calibers like 9mm submachine guns, 22LR, 45ACP, 38 Special, rocket pistol, 444 Marlin, bow and arrow, were also tried... The hammer was air support, regardless of which small arms were used.

Yeah, and they had explosive arrows for their bows. We all saw Rambo..

 

[45-90]

No they did not use explosive arrows...movies aside...
You're behind enemy lines in another country, it was applied briefly a try at being stealthy. The rocket pistol was another attempt.
When you're surrounded by large groups of enemy, numbering in the thousands, contact is not what you want.
Study & observations group, report back, troop movement & strength, call in air strikes, take a prisoner, evacuate the area by helicopter.
Tactics were more important then personal weapons, if which there were a variety, for different reasons, silenced 22 LR to drop back and ambush the SOG hunters.
When contact happens, tactics and map reading to get air support or evacuation are top priorities for getting out alive.

 

[Hecouldgoalltheway]

No they did not use explosive arrows...movies aside...
You're behind enemy lines in another country, it was applied briefly a try at being stealthy. The rocket pistol was another attempt.
When you're surrounded by large groups of enemy, numbering in the thousands, contact is not what you want.
Study & observations group, report back, troop movement & strength, call in air strikes, take a prisoner, evacuate the area by helicopter.
Tactics were more important then personal weapons, if which there were a variety, for different reasons, silenced 22 LR to drop back and ambush the SOG hunters.
When contact happens, tactics and map reading to get air support or evacuation are top priorities for getting out alive.

Interesting. I wish I had been trained in small unit tactics in the army.


Oh yeah, I was, extensively.

Never got any rocket pistols or bows and arrows though.

 

[ut755ln]

I can see 6 Max potentially being of interest to the USMC down the road as an upgrade to the M27 IAR, depending on what bullets end up being cooked up for it

They are currently testing 6 ARC with uppers from HK.

 

[45-90]

Interesting. I wish I had been trained in small unit tactics in the army.


Oh yeah, I was, extensively.

Never got any rocket pistols or bows and arrows though.

You needed to sign up for MAC V SOG, in the late 60s where one could alter weapons, acquire full auto foreign weapons at your request, 1 bow by a former archer, one 444 Marlin to alter the face of the enemy requested and recieved, the use of AKs was very common at first to blend in...then everyone "acquired" American weapons throughout the whole area on both sides of the border.
You were an unidentified combatants, no country, no identification, 100% casualties 58% killed, sometimes everyone in the insertion disappeared without a trace.
But one could carry or alter his weapon anyway he chose for the mission...but the choice might get someone killed...like the rocket pistol...