What do you think of the 6mm ARC?

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DocT

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What do you all think of the new 6mm ARC?

It was requested by a US Special Forces organization that Hornady make such a cartridge, apparently. It has greater power than the 5.56 and better penetration on body armor, with not much recoil. It has greater down range energy at 600 to 1000 meters than the 7.62/308, is flatter shooting, and has better penetration at those ranges. It has far less recoil and good barrel life. it uses heavy for caliber bullets that other .243/6mm SAAMI cartridges cannot use. Therefore the BC is higher than anything a 6.5mm or 7.62mm can achieve. It attains a velocity of 2750fps from an actual 24" AR barrel and even at 18" is still clocking in the mid 2600's.

What are your thoughts?
 
While that article made a few good points it is mostly full of inaccuracies and bad suppositions. There are too many to go into now, but anyone actually researching this cartridge will spot them easily.
 
Looks similar to the 6 PPC, not a great round for magazine fed rifles.
 
Don’t we already have enough 6mm cartridges? What does it do that others don’t? Well it seems like “.243 light” to me, about 200 FPS less. It won’t fave recoil similar to 5.56 if it has 108 grain bullets vs 60-something grain bullets. And why talk about 24” barrels? Nobody in the military that uses this cartridge would have a barrel that long. Otherwise if it meets their spec then more power to them.
 
The 243 can only take and stabilize the 100gr bullet and has a lot more recoil. The 6mm ARC uses less powder at lower pressure, so less recoil.
 
DocT said:
The 243 can only take and stabilize the 100gr bullet and has a lot more recoil. The 6mm ARC uses less powder at lower pressure, so less recoil.
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Well yes, about 7% less velocity means a little bit less recoil.
What bullet it takes and stabilizes is a function of the barrel more than the cartridge, with the same barrel specs the .243 would actually stabilize the longer projectile better via its higher velocity.
 
bdmicarta said:
Well yes, about 7% less velocity means a little bit less recoil.
What bullet it takes and stabilizes is a function of the barrel more than the cartridge, with the same barrel specs the .243 would actually stabilize the longer projectile better via its higher velocity.
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SAAMI specs the .243 with a twist that will not deal with heavy for caliber bullets well. But, as you say, you could go through the expense of rebarreling a rifle. But that is not the only issue. The .308 case is an older design and not as efficient as the Grendel case. It requires more powder to achieve those velocities (I still love the .243) and more powder burning means more recoil. It is not just velocity. Plus, the heavy for caliber, ultra high BC bullets retain energy and flat trajectory far in excess of what a mere velocity table will tell you. That is why is out performs the .243. So, for military purposes, the 6mmARC makes a huge amount of sense because of the low recoil, retained energy, and flat trajectory out to 1000 meters.
 
Hornady lists the bc of the 6mm 108 eld at .536 @ mach 2.25. That's pretty good, I consider anything over .4 to be pretty magical.
They also list the 6.5 130 gr eld at .554 and the 7.62 178 gr at .547 those are higher. I generally don't think it's fair to compare cartridges from one sized platform with another but you did, so here are my thoughts. If you're comparing ballistic coefficients and 1000 yard reliability bigger is better. I'm not saying any given round out of an ar15 isn't capable of 1k shots, but to say the 6mm arc will do it better than a larger round in the same caliber because of saami specs is not necessarily true. The saami drawing on the .243 does give a 1:10 rh twist, but the next word is "optional". My ruger 77 mk 2 has a 1:9 twist, and there are ar10 .243 uppers with 1:8. That's enough to stabilize the 108 led. If the .243 is too old and inefficient, there's the 6mm creedmoor. It chucks that same 108 eld pill around 3k fps. I'm not suggesting either of those rounds would be my choice. Hell if I wanted a 1000 yard gas gun it would probably be the 6.5 creedmoor.
The arc may be a fine round, but in all honesty if I wanted a 6mm in an ar15 it would be the 6mm tcu.
 
oof said:
Hornady lists the bc of the 6mm 108 eld at .536 @ mach 2.25. That's pretty good, I consider anything over .4 to be pretty magical.
They also list the 6.5 130 gr eld at .554 and the 7.62 178 gr at .547 those are higher. I generally don't think it's fair to compare cartridges from one sized platform with another but you did, so here are my thoughts. If you're comparing ballistic coefficients and 1000 yard reliability bigger is better. I'm not saying any given round out of an ar15 isn't capable of 1k shots, but to say the 6mm arc will do it better than a larger round in the same caliber because of saami specs is not necessarily true. The saami drawing on the .243 does give a 1:10 rh twist, but the next word is "optional". My ruger 77 mk 2 has a 1:9 twist, and there are ar10 .243 uppers with 1:8. That's enough to stabilize the 108 led. If the .243 is too old and inefficient, there's the 6mm creedmoor. It chucks that same 108 eld pill around 3k fps. I'm not suggesting either of those rounds would be my choice. Hell if I wanted a 1000 yard gas gun it would probably be the 6.5 creedmoor.
The arc may be a fine round, but in all honesty if I wanted a 6mm in an ar15 it would be the 6mm tcu.
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I don't consider the .308 case to be inefficient, but it might be bigger than needed for the job at hand. The .243 achieves "super magnum" ballistics without even saying it in the name. The .243 had factory velocities of 3500 fps a whole long time ago, and with bullets available now you can get nearly 4000 fps.
But back to the original subject- pick the goal for the cartridge and then go from there. If you only want 108 grains at 1000 yards then this is a good cartridge. For that matter people in highpower competition are using 80 and 90 grain bullets in their .223, those certainly have good BC and will be pretty efficient out to 1000 yards, although like you said larger calibers always offer better BC at the limits. I always thought 6.5mm was a better diameter if you really wanted 1000 yard performance, not that I would want someone shooting at me at 1000 yards with a 6mm of any sort.
Another question would be why are we talking 1000 yard performance? Why does the military think that is needed? An AR platform with short barrel and open sights or low powered optics, on the battlefield, isn't really conducive to precision shooting at long distances. And they already have specialized sniping platforms.
And if you really want 1000 yard performance for military use, you probably want more than 108 grains being delivered at that distance so you probably need to go up to 7mm diameter. If I remember right the ballistics of the ARC will keep it supersonic to 1000 yards, so is 108 grains at 1300 fps a significant military result?
 
The whole point is to have a more effective cartridge. ISIS etc. have learned the maximum effective range of the 5.56. The 6mm ARC extends that range and penetrates body armor far better. The ARC does this with the least recoil possible making follow up shots faster and more accurate. There are a whole list of reasons the Special Forces wanted this cartridge, not one of which is actually being addressed. It is true that there are faster cartridges. Speed was not the main issue. It is true that the .243 can be had with other barrel twists, but that is not the issue. Effective against armor, has a greater effective range, low recoil, has an adequate combat load (larger cartridges do not) at an acceptable weight, and more. It was not designed as a long range deer cartridge or target round.
 
I'm not going to second-guess special forces on what they need, but do I wonder about the advantages of this round for short-barreled rifles in shorter distances where more rounds is better. As a replacement for .308 for DMR in a 18-20" barrel, I guess it's an incremental step up if you want to stay with the AR platform? But in that case why not 6.5 creedmore with a good muzzle brake in a lightweight ar10 build - just for longer barrel life?
 
fishface5 said:
I'm not going to second-guess special forces on what they need, but do I wonder about the advantages of this round for short-barreled rifles in shorter distances where more rounds is better. As a replacement for .308 for DMR in a 18-20" barrel, I guess it's an incremental step up if you want to stay with the AR platform? But in that case why not 6.5 creedmore with a good muzzle brake in a lightweight ar10 build - just for longer barrel life?
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I don’t remember. There was a good reason they did not choose the 6.5’s. One is they wanted to keep the light and handy AR15 platform, another recoil, the ARC is faster than the Glendale, uses low pressure, but I seem to remember there was another Reason I can’t recall right now.

it is fascinating in any case. I would not choose this as my favorite deer cartridge, but it does seem to meet some real needs that have been discussed for 50years, and more so since we went to the Middle East.
 
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DocT said:
The whole point is to have a more effective cartridge. ISIS etc. have learned the maximum effective range of the 5.56. The 6mm ARC extends that range and penetrates body armor far better.
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It doesn't seem like that big of an increment over what they have, but maybe they know what they want. If they are going to keep the current AR platform that limits the case size a bit. Personally I think I would go for a bigger increment but with the current AR platform you can increase projectile size or you can keep high velocity, it is hard to do both. If you want more horsepower you have to buy new receivers and so forth instead of just new bolts and barrels.
I've seen experiments where people tried to gain a bit more horsepower out of the AR by going to the .22PPC case and 90 grain bullets. The cartridge OAL starts to become a problem requiring careful magazine modifications. They do gain a little more power but starts to become impractical.
It has recently seemed to me that we have plenty of different cartridges, why bother to invent new ones? Doesn't a current cartridge case satisfy the need? So I scanned through a Hornady manual- if .243 case is too big then there are plenty of cases slightly smaller that could likely work without having to invent something new.
However the answer is that people want to make things complicated, and there is the "not invented here" issue. It is salesmanship- a company wants to invent their own thing, put their own name on it, and promote it as something new and better even if it is 99.9% identical to a 50+ year old cartridge. People that don't know the difference buy into it, people who do know the difference just shake their heads and groan.

Edit- I looked up information online and it appears that the ARC is 99.9% the same as the 6PPC and very similar to the Grendel case. People have been using variations of these in highpower competition for years. With a case that small the ballistics could be questioned but Hornady should be good at ballistic measurements. The difference these days is that we have some powders available that improve performance a bit, but that could apply to the competing cartridges as well. Staying with the current AR platform then 6ARC and 6.5Grendel somewhat define the limits for bore diameters slightly over .223.
 
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Yeah, the ARC is not the end-all of cartridges but it does what none of the others that are standardized will do. Many others are not standardized. Hornady went through the problem of getting SAAMI standardization during development. It could have been a faster cartridge that it is, but the idea of keeping the pressure low for longer service life of the AR's and keeping down recoil mean that it is about as fast as it can go. What is going to be interesting is to see the actual results in the field. Oh, and it should be said that it turns out that Hornady's 'test' barrels were real commercial AR barrels like one would get on a top quality AR. They wanted the results in real use to be the same as they got with their testing. Smart. The results are from 24" barrels, but even at 18" the cartridge performs well.
 
DocT said:
The results are from 24" barrels, but even at 18" the cartridge performs well.
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I can't imagine the average military using 24" barrels. They had 20" and those were too long, now they are using barrels that would be right at home on a Thompson Contender. Barrel length probably doesn't make as much difference for the smaller case as it would for one of the super big cases that are popular these days.
 
I know this thread is long dead but as an owner of 2x 6mm ARC builds I want to weigh in.

"But in that case why not 6.5 creedmoor with a good muzzle brake in a lightweight ar10 build - just for longer barrel life?"
The AR-10 platform is not generally known for it's reliability or ease of working out the kinks, there is parts compatibility issues as well as the fact that most of the "lightweight" versions of the AR-10 are either filled with proprietary components or still nowhere near as light as an AR-15. The AR-10 over the AR-15 platform not only brings more weight and a larger footprint but also more cost. Building an AR-10 in 308 even using budget components vs a budget AR-15 is double the price.

Factory loads coming out of my 20" barreled 6mm ARC are going ~2700fps with a 103gn projectile. Once the BC is figured in you have a round with over 900 ft/lbs at 400 yards and just over 30" of drop. Most hunting will be done well within that distance but having the ability to make those kind of shots accurately in a lightweight, familiar, easily modified package provides a lot of benefit to the shooter/hunter. With a muzzle brake on it, a rifle length gas system and the reciprocating mass of the bolt and buffer system eating a good bit of the energy it becomes more manageable than a stock configuration carbine length 5.56 AR-15. Speed of follow up shots are more likely to be a measure of the optics system you are running than the gun. I can say with surety that the projectiles being produced for hunting and match in the 6mm ARC are also quite superb, great expansion and penetration. I regularly hunt Big Texas Feral swine with the round and have not had a single one do anything other than fall over dead in it's tracks. Small entrance wounds, punched right through Boar shields and ribs and dump all their energy into the vitals.
 
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