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Hornady 6mm ARC Cartridge - What You Need to Know

Developed for use with an AR-15 rifle, how does the Hornady 6mm ARC stack up to other popular AR-platform cartridges?

Hornady 6mm ARC Cartridge - What You Need to Know
New from Hornady is their 6mm Advanced Rifle Cartridge or ARC which is specifically designed to extend the range and improve the performance of an AR-15 rifle.

Big news from Hornady Manufacturing who officially released their new 6mm ARC cartridge. The question is, why was it developed and what does it actually bring to the table. Basically, most readers want to know if they should bother to pay attention to the new 6mm ARC, or will it simply fade away in a year, like so many do? Let’s start by taking a brief look at the cartridge itself, then move into what it was designed to accomplish and then into if it might be right for you.

Hornady-6mmARC-2
Hornady engineers used the 6.5mm Grendel as the starting point for developing the 6mm ARC to meet the needs of a DoD entity.

6mm ARC

The new Hornady 6mm Advanced Rifle Cartridge, or ARC, is based off another very popular design, the 6.5mm Grendel. It is not simply a necked down Grendel though, rather the engineers at Hornady made some changes to the case design to optimize it for their needs. It shares the same .441-inch diameter casehead with the 6.5mm Grendel as well as the .220 Russian and 7.62x39mm. The neck though has been moved back to facilitate loading the very long for caliber 6mm projectiles. Shoulder angle has also been tweaked. It shares the thicker .059-inch rim of the 6.5mm Grendel which is significantly thicker than the .038-inch rim of the 5.56x45mm. This aids reliability. As they have the same casehead diameter the 6mm ARC utilizes the same AR-15 bolt as the 6.5mm Grendel. These are readily available and of known quality.

While the 6.5mm Grendel was designed around .264-inch projectiles running from 95 to 144-grains, the cartridge is at its best with projectiles weighing from 107 to 123 grains. The 6mm ARC on the other hand is designed around modern .243-inch projectiles running from 103 to 108 grains. It was specifically designed to utilize very long for caliber projectiles with very high Ballistic Coefficients to enhance exterior ballistics. For example, the Hornady 108-grain ELD-Match bullet has a G1 BC of .536. This is substantially higher than either a .308-inch 175-grain Sierra MatchKing or a .224-inch 77-grain Sierra MatchKing. Advertised velocity of the 6mm ARC 108-grain ELD-Match load is 2,750 fps from a 24-inch barrel.

Hornady-6mmARC-2
Hornady is launching the 6mm ARC with three loads running in weight from 103 to 108 grains at about between 2,750 and 2,800 fps from a 24-inch barrel.

One very important aspect of both its parent cartridge and the 6mm ARC is they were both specifically designed to function in an AR-15. This means their diameter and overall length are dictated by the confines of the dimensions of a STANAG magazine. These dimensions are the biggest hurdle to overcome when designing a cartridge that offers superlative performance in an AR-15 while also functioning reliably. Bolt design also comes into play as well, and Bill Alexander, the designer of the 6.5mm Grendel, spent a considerable amount of time designing a Colt pattern bolt with a long service life.


Hornady is launching the new cartridge with three loads. The first is a 103-grain ELD-X Precision Hunter. This hunting load has a G1 BC of .512 and an advertised velocity of 2,800 fps from a 24-inch barrel. The second is a 105-grain BTHP Black. This has a G1 BC of .530 and an advertised velocity of 2,750 fps from a 24-inch barrel. Lastly there is their 108-grain ELD-Match load with a G1 BC of .536 and an advertised velocity of 2,750 fps. How do these stack up compared to a 5.56x45mm Mk 262 Mod 1 77-grain OTM? The 6mm ARC’s more efficient projectiles with their high BCs provides superior exterior ballistics with noticeably less wind drift, higher retained velocity and greater retained energy. So, the 6mm ARC outperforms any magazine length 5.56x45mm NATO load simply through a combination of sheer horsepower and more efficient projectiles.


Hornady-6mmARC-2
The US Army developed the 6mm SAW cartridge (center) which showed great potential, it is seen here flanked by a .224 Valkyrie (L) and 5.56x45mm NATO (R).

What about compared to the .308 Winchester? As the 6mm ARC is a dramatically smaller cartridge than the .308 Winchester at first glance you wouldn’t think there would be any comparison at all, and in some respects there isn’t. However, in some areas the 6mm ARC does dominate the .308 Winchester or at least maintains parity. As a cartridge is part of a weapons complex, everything must be taken into consideration. In this regard, the 6mm ARC neatly fits into a weapon platform that is dramatically smaller and lighter than a traditional AR-10 platform required by the .308 Winchester. So, the weapon system is smaller and lighter, more maneuverable and less fatiguing to carry. The ammunition is also dramatically lighter allowing more rounds to be carried compared to a .308 Winchester platform. Recoil impulse is also significantly less than a .308 Winchester, allowing a rifleman to easily spot his own shots, while also decreasing his time between shots. All of these points increase a soldier’s survivability on the modern battlefield.

When it comes to external ballistics, the 6mm ARC 108-grain ELD-Match load will outperform a traditional 175-grain M118LR OTM load when it comes to wind drift and drop while retaining velocity better. However, the M118LR OTM puts a much larger and heavier payload on target and has significantly more retained energy. When it comes to terminal performance the M118LR will also have an advantage at practical ranges. Now, these comments are stated comparing a 24-inch barrel to a 24-inch barrel. Cut the barrel back on the 6mm ARC and velocity will indeed drop, but the same is true of the .308 Winchester. Switching to a more modern projectile, such as Sierra’s 175-grain Tipped MatchKing, with its higher G1 BC, tips the scales and puts the two on fairly even ground when it comes to external ballistics.

Hornady-6mmARC-2
Hornady’s new 6mm ARC easily outperforms traditional 5.56mm loads like the 77-grain Mk262 Mod 1.

What was 6mm ARC Designed for?

Why do I mention “a soldier’s survivability on the modern battlefield” when discussing the 6mm ARC? I mention it because Hornady originally designed the cartridge at the request of a Department of Defense customer. So, the cartridge was not originally conceived for competition or hunting. As you delve deeper into the cartridge, this begins to become obvious. It is also why I compared the 6mm ARC to the 5.56x45mm 77-grain Mk 262 Mod 1 and 7.62x51mm 175-grain M118LR loads. These two loads would be its traditional competition, although both are admittedly now growing long in the tooth.

According to statements from Hornady, a DoD entity requested a cartridge with certain capabilities. The engineers at Hornady initially moved to fill their request with the 6.5mm Grendel cartridge. This makes sense, as the cartridge was originally designed by a British engineer who had worked at their MoD and by a Finnish engineer at Lapua, which is well known for their military products. The 6.5mm Grendel cartridge was originally developed to be suitable for military use, underwent rigorous testing, including full-automatic and had specialized AP loads developed for it. Small quantities were fielded in Afghanistan and it is currently the standard DMR cartridge of Serbia.


Unfortunately, as good as the 6.5mm Grendel is, it does have certain limitations. These cropped up during Hornady’s initial testing. For military use the 6.5mm Grendel has four noteworthy shortcomings. These are: ammunition weight, recoil impulse, ability to penetrate intermediate barriers and the dimensions of the STANAG magazine well. I’ll cover the first three here the fourth later. Compared to 5.56x45mm ammunition, a 123-grain 6.5mm round is significantly heavier. It is almost twice as heavy, which drastically reduces a soldier’s ammunition load. 6.5mm Grendel ammunition weighs about the same as 7.62x39mm. This is a huge negative.

Hornady-6mmARC-2
The 6mm ARC’s exterior ballistics are good, enough thanks to its use of high BC projectiles, to allow it to run with the .308 Winchester when shooting long.

The recoil impulse of the 6.5mm Grendel is also significantly heavier than 5.56x45mm. It is also much harder to control on full-automatic. The recoil impulse of the 6.5mm Grendel is actually heavier than that of the 7.62x39mm. So, compared to the 5.56x45mm the Grendel’s heavier recoil impulse is also a negative. On the flip side, it is significantly less than a .308 Winchesters.

According to statements made by Hornady, the ability to penetrate intermediate barriers at distance was also an issue with the Grendel. This makes sense as the Grendel’s velocity is relatively modest at around 2,550 to 2,600 fps and the projectile is larger in diameter with less sectional density compared to a modern 6mm. When it comes to penetrating intermediate barriers impact velocity, projectile design, projectile weight, projectile diameter and sectional density all come into play. A higher velocity, smaller diameter projectile with greater sectional density will have an edge.


Does a 6mm Make Sense?

So, the next question would be, does a 6mm cartridge actually make sense for military use? If you look at the major players in the world, the US, Russia and China, they adopted cartridges of 5.56mm, 5.45mm and 5.8mm. But if we look a bit deeper at the Chinese Peoples Liberation Army’s research and studies leading up to the development of their 5.8x42mm cartridge we find some interesting information.

Noting the advantages of the small, high velocity 5.56x45mm cartridge used by US forces, the Chinese began extensive research and theoretical studies based on their combat observations of the war in Vietnam. Their goal was to find the ideal caliber to satisfy the Chinese military requirements for use in assault rifles out to medium ranges (400m) as well as in the supporting role of a machinegun (up to 1000m). Their intention was not just to build a series of weapons based on an existing cartridge but rather build a weapons complex using the “ideal” cartridge. This "Universal caliber" had always been a Holy Grail for which many have sought but none had found.

Hornady-6mmARC-2

After extensive calculations they concluded that the ideal caliber would be 5.8mm, 6mm, or 6.2mm. They then designed a vast assortment of prototype cartridges for use in comparison testing. This is similar to the US Army’s SAW project which tested over 1,000 configurations in calibers ranging from 5.56mm to 7.62mm. The final result of this US project was the 6x45mm SAW round, which showed great promise. However it was never adopted due to logistical reasons.

This shows the US and Chinese designers came to a similar conclusion as to the ideal caliber. Based on their test results the Chinese came to the final conclusion that the 5.8mm best fit their needs. The result was their small caliber, high velocity 5.8x42mm cartridge. The PLA placed heavy emphasis on penetration during the development work on the 5.8x42mm, and did a great deal of testing. So, Hornady’s development of the 6mm ARC does make sense in light of both the Chinese research and US work on the 6mm SAW project for the specific application Hornady states the 6mm ARC was developed for.

Is the 6mm ARC Right for You?

What about for you? Only you can decide that but, there are certain pros and cons to the 6mm ARC. If you are looking for a step-up in performance over the 5.56x45mm for use in an AR-15, but accuracy, external ballistics, recoil impulse and ammunition weight are a concern, than maybe. The 6mm ARC has the potential be a very accurate cartridge. It is not limited to use in an AR-15 either, and would work well in a micro-action bolt gun. For use in certain gun games shooting steel at distance it will likely work very well. The light recoil will allow you to spot your shots, while the high BC projectiles will provide an edge over lessor cartridges. The 6mm ARC easily outclasses the 5.56x45mm 5.45x39mm, 5.8x42mm and 7.62x39mm. It also offers advantages over both the .22 Nosler and .224 Valkyrie. It puts a heavier and larger diameter payload on target than either of these. Plus, velocities are very similar and the BCs of the 6mm projectiles generally outclass their .224-inch competition.

Hornady-6mmARC-2
Here is a look at how barrel length effects the velocity of Hornady's 108-grain ELD Match load. Notice that even a 12-inch barreled 6mm ARC has a higher muzzle velocity than a 16 inch 7.62x39mm AKM and better exterior ballistics across the board.

What about drawbacks to the 6mm ARC? The only real issue I see is the dimensions of the AR-15 magazine well. This dictates the external dimensions of the magazine. The use of the 6.5mm Grendel base cartridge dictates the internal dimensions of the magazine. There is very little room between the two. Due to this it’s not possible to produce polymer 6.5mm Grendel magazines. There simply isn’t enough room. Grendel magazines are typically produced from thin stainless steel. Some work great, others give issues.

Magazine issues are the only real drawback to the 6.5mm Grendel and the 6mm ARC will have similar issues. The perfect solution would be what LWRCI did with their SIX8 6.8x43mm Rem SPC project. They changed the magazine well dimensions, made it larger and optimized the magazine for the cartridge. I have always stated this is what the 6.5mm Grendel needs. But no one wants to move away from the STANAG standard. That said, a good 6.5mm Grendel magazine runs flawless and magazines have improved since the cartridge was introduced in 2004.

What about the 6mm ARC compared to the 6.5mm Grendel? Depends upon what you are going to use it for. For hunting whitetail deer, pigs and similar sized animals I would still take the 6.5mm Grendel. It’s a proven performer in the field which puts a larger diameter and heavier bullet on target. For ringing steel at distance, I’d lean towards the 6mm ARC. It depends upon what your needs are. At the time I am writing this, the 6.5mm Grendel has many more loads available for it, and economical steel case ammunition from Wolf. But all this can change over time.

Will the 6mm ARC take off in popularity? Here my crystal ball is foggy. In my opinion, for any cartridge intended for use in a semi-automatic platform to become hugely successful it requires one critical component, inexpensive ammunition. No one except low volume competition shooters want to spring $20+ a box for ammunition or spend time chained to their reloading bench. The 6.5mm Grendel never took off until Wolf Performance Ammunition introduced economical steel case ammunition. Once they did, it exploded in popularity. The good news with the 6mm ARC is it’s based on the 6.5mm Grendel. Why is this important? It would be relatively easy for Wolf Performance Ammunition to introduce a steel case 6mm ARC load. Economical 6mm ARC? That would be a recipe for success.

Hornady’s 6mm ARC is a very interesting cartridge, although the concept of a 6mm Grendel/PPC has been around for a very long time. The difference here is it’s a production piece with a highly respected manufacturer behind it. The exterior ballistics look very good, it should be very accurate if the chamber/throat is properly designed. Competition shooters looking to stretch the reach of their AR-15s will take notice of it. Firearms News will be delving deeper into this new cartridge in issue 14, so keep an eye out for it at the newsstand. Until then here are two videos from Hornady which will provide you with more information on their new 6mm ARC. Plus for more information visit www.Hornady.com.

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