6mm ARC: The Best Long-Range AR Round Ever?

By Rob Leatham
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6mm ARC: The Best Long-Range AR Round Ever?

November 5th, 2021

7 minute read

In my opinion, the 6mm ARC (Advanced Rifle Cartridge), is the king of long-range shooting. Now, that obviously needs some explaining.

Over the last two years, I have become enamored with long-range rifle shooting in general and Precision Rifle Series (PRS) competition in particular. Why? These matches test the ability of both you and your equipment to hit small targets way out there. It’s frustrating, challenging and fun.

Box of Hornady 6mm ARC ammo
Is this the king of long-range shooting? The author offers compelling reasons to support the idea.

The majority of shots at my local events are between 400 to 700 yards — with a few out to 1,000 thrown in for good measure. But distance is only one factor in the challenge of making impacts. Most of the shots are fired while trying to get steady off improvised props. There is some prone shooting, but the vast majority is off logs and barrels and fences and sometimes worse.

Targets are placed randomly all over the desert and surrounding hills. The sizes of the targets vary, and distances are not evenly graduated. So, think more like 562 yards rather than 550 or 575.

These matches are designed for and ruled by the magazine-fed, bolt-action rifle. But there is a division specifically for the semi-auto platform called Gas Gun. This has been my passion of late. (Learn more about Rob’s gun builds for PRS.)

"Baby BeAR" 6mm ARC rifle
The “Baby BeAR” roars. Here, the author engages a target with one of his modified Springfield SAINT 6mm ARC rifles.

But Why Not … ?

Before you hit me with, “My .223 can hit all those targets!”, let me explain. It probably can. Maybe. But the point isn’t just being able to hit the targets — .223 just doesn’t have enough impact against the target. Remember, if the spotter can’t confirm the hit, you don’t get it.

Even with the best .223/5.56 ammo that will fit in the AR-15 magazine (most commonly 77-grainers at about 2,750 fps), it won’t have enough juice when it gets there. Bullet weight is important — even more than velocity — and you will always have to consider drop and wind drift compared to other options.

So, what do you do? Remember those options I just mentioned?

Rob shooting PRS with a modified SAINT Victor .308 rifle
Here the author is shooting a modified SAINT Victor .308 in 6.5 Creedmoor during a Precision Rifle Series competition.

6.5 Grendel can launch 130-gr. bullets of high ballistic co-efficient (BC), but it is very slow — but still better than .223. The .224 Valkyrie is a vast improvement, sending very high BC bullets at reasonable velocity. It’s one of my favorites and has stretched the AR-15’s effectiveness to distances much farther than the .223 can. Still, more would be nice. It always is …

In the PRS world right now, the rage is a 6mm 105- to 110-gr., very-low-drag (VLD) bullet with very high ballistic coefficients. Those bullets reduce both bullet drop and wind drift at longer ranges. And you wouldn’t think this, but they are not after the highest possible speed — not at the cost of recoil and gun movement, as this aids the shooter spotting hits and misses. The rules allow up to 3,200 fps maximum speed, but many of the top shooters think around 2,850 fps is optimal. This gives you great ballistics with the lightest possible recoil.

It is crucial for the shooter to be able to see real-time hits and misses so they can correct on subsequent shots. So, recoil matters.

Another Option

Being a gear geek, I have explored and experimented with just about every long-range cartridge variation in the AR (both 5.56 and 7.62) platform. I always had to go to a 7.62 AR to get the needed ballistics. But not anymore.

Enter the Hornady 6mm ARC. The 6mm ARC is optimized to deliver a heavy, high BC, very low drag (VLD) bullet at the highest velocity possible, while still being small enough to fit into the small frame AR-15 magazine dimensions.

Rob Leatham with .224 Valkyrie SAINT rifle
The author engages targets with his Springfield Armory SAINT he chambered for the .224 Valkyrie cartridge.

The 6mm ARC pushes small frame AR-15 long-range capability to new heights with factory available ammo. You get a 103- to 108-gr. bullet going 2,750 fps out of a 22” barreled AR-15. This is no small feat. It may not be the magic 2,850, but it is close and it doesn’t require the larger frame of a 7.62 AR.

The 6ARC has legit long-range capability.

I’ll tell you now that I am an ARC convert. I get 90% of my large-frame AR 6mm Creedmoor’s speed in the smaller, lighter and more compact 5.56 AR platform. Using dramatically less powder, it is believed that the barrel on an 6mm ARC will far outlast a 6mm Creedmoor’s. It kicks less and has very similar performance regarding wind drift, which after accuracy and consistency is the biggest issue for long-range shooting.

All of this makes the 6mm ARC the best AR magazine-fed round for long-range use in my opinion.

My Setup

Let me give you my basic recipe for my 6mm ARC rifle.

I start with a Springfield Armory SAINT Victor. This gets me most of what I need right out of the box. Our SAINT Victor AR .223/5.56 line of rifles come with 16” barrels that function well and are very accurate. When the basic gun you start with works, everything else is a snap.

Essentially, the 5.56 AR needs just three things to become a 6mm ARC: a barrel, bolt and magazine. I change the gas system port location on the 6mm ARC barrel from the mid position of the SAINT 5.56, so I also need a gas tube.

You can build your 6mm ARC into the existing SAINT 5.56 upper assembly or start a whole new upper and keep your awesome .223 assembly intact. That’s what good receivers, handguards and bolt carrier groups do for you. Interchangeability is very nice. This will give you a multi role platform. I have done it both ways with great results. 

106-gr. TAP round of 6mm ARC fired into ballistic gelatin
The 6mm ARC has a lot of power compared to the .223. A 106-gr. TAP round is shown here fired into ballistic gelatin.

Story Time with Uncle Rob

Let me tell you about “The Three BeARs”.

Baby BeAR has an 18” Proof Research steel barrel with a rifle length plus 1” .750 gas system and muzzle diameter of .735. It has a 1 in 7.5 twist and prefers to eat Hornady 108-gr. ELDM Match ammo. This is my lightest and shortest 6mm ARC and currently has an old but very functional Surefire suppressor on it. It was my first ARC and has the most “experience.” The lower is fitted with a TriggerTech Diamond trigger.

Mama BeAR is a 22” barrel made from a re-purposed 25-year-old Krieger .236 bore steel barrel (off an old .243 bolt gun I had). It was turned down from its bull-barreled profile by my friends at MOS-Tek and has a rifle length plus 1”.875 gas system with .855 muzzle diameter. It is a 1 in 7 twist and currently sports a barrel tuner from Kinetic Security Solutions and an Area 419 Hellfire muzzle brake. This one prefers the Hornady 103-gr. ELDX hunting load and has an ATC ARGOLD flat trigger installed.

Three of Rob Leathman's "Little BeARs"
All three of Leatham’s “Little BeARs” in 6mm ARC, including the 19-lb. beast on the far right.

Papa BeAR is the beast (LOL) of the family. He’s a huge 24.5” Proof Research steel barrel turned at MOS-Tek with a rifle length plus 2” .936 gas system and muzzle diameter of .915. Papa BeAR’s barrel is about as big and long as is prudent for an AR-15. It’s very possibly too big. This one is built on an Aero Precision enhanced upper and hand guard with an Area 419 Hellfire muzzle brake. Since AR 15s have great standardization, many parts should be interchangeable. I’ve found that a good upper fits perfectly on Springfield’s SAINT lowers. 

Making Papa even more outrageous, he has steel weights on the forend which get its total up to nearly 19 pounds with bipod. It does not kick much but it is, dare I say it, a “bear” to move from position to position. Papa shoots all 3 loads OK but is best with the 108 ELDM Match. He’s not everyone’s cup of tea, but a great shooter and very interesting experiment. This lower also sports an American Trigger Corporation AR Gold flat trigger.

All three of my BeARs have many things in common. The most important part regarding accuracy is the barrel.  Magazines, port position, port size and bolt carrier group (BCG) are the most important parts regarding reliability.

Since the 6mm ARC uses a larger than .223/5.56 rim diameter, it needs a new, larger-faced bolt. I have switched to the appropriate JP 6mm ARC bolts installed into the factory bolt carriers. Again, it is nice to have quality parts to begin with.

6mm ARC headstamp
As the author demonstrates — both in the article and on the range — the 6mm ARC is a formidable cartridge.

All currently have Magpul PRS Gen3 stocks on them with the standard Springfield SAINT carbine length buffer tubes. This is a personal preference for a PRS-type gun and is not required.

They all use the standard SAINT springs and buffers, lowers, grips and pins and things.

All of my AR’s for long-range work have ARCA rails installed on the nice long SAINT Victor handguards. This is easy to do with the M-Lok slots that come standard on the Victor free-float handguards. This allows easy mounting and positioning of bipods and mounting the gun to tripods. 

Since you can’t hit what you can’t see, I have chosen to go with premium optics — all from Nightforce. I swap them around amongst my 5.56 AR and 7.62 AR SAINT rifles all the time. Currently, Baby BeAR has an ATACR 4-16×42, Mama an ATACR 4-16×50 and Papa an ATACR 7-35×56. These are all easy to sight in and zero the knobs.

Conclusion

As my preference for the AR and modern sporting rifle (MSR) pattern rifle grows, I have learned a surprising thing: Properly set up and in the right caliber with its preferred ammo, my Gas Gun can hit everything my bolt gun can.

As I stated earlier, 6mm ARC is the king of long-range AR guns.

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Springfield Armory® recommends you seek qualified and competent training from a certified instructor prior to handling any firearm and be sure to read your owner’s manual. These articles are considered to be suggestions and not recommendations from Springfield Armory. The views and opinions expressed on this website are those of the authors and do not necessarily reflect the views and opinions of Springfield Armory.

Rob Leatham

Rob Leatham

Rob Leatham, captain of Team Springfield, has been with the Springfield Armory family since the late 1980s. He is a world-renowned competition shooter and firearms instructor who is highly regarded as one of — if not the — most-winning Practical Pistol Competitor in history. Rob's sheer number of National and World Shooting Titles make him unique in the firearms industry. He has trained shooters from all walks of life — from IPSC World Champions to Military Special Forces Operators and from Law Enforcement Officers to civilians for Self Defense. In the competitive shooting world of IPSC, USPSA, Steel Challenge, IDPA and NRA Action Pistol, Rob’s competition career has spanned decades.

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