New cartridges can be a roll of the dice for ammo and gun manufacturers. One thing that can really give a new cartridge a boost is military use and legitimacy, and the 6mm Advanced Rifle Cartridge (ARC) earned that elite status before ever hitting retail shelves.
I got my first hint of the 6mm ARC at the 2020 SHOT Show, and an invitation to join Hornady’s Marketing Manager, Neal Emory, on one of his favorite Wyoming ranches a month later to bust some coyotes. During the hours Neal and I spent together when the dogs weren’t cooperating, I learned that a secretive DoD entity has adopted the 6mm ARC for combat operations as a replacement for the 7.62x51mm NATO, (.308 Winchester in civilian terms). A casual observer might scratch his head as to why a military unit would want to field a .243 caliber battle rifle, but a closer look makes it clear.
The 6mm ARC’s parent case is the 6.5 Grendel, which takes its lineage from the .220 Russian and 7.62mm Soviet. Since Hornady was the first ammo maker to get behind the 6.5 Grendel in a big way, it was an easy transition to the new round. As an offspring of the Soviet 7.62×39, the 6mm ARC get some of the shared battlefield cred, too.
By the numbers, the 6mm ARC case head measures 0.440, just 0.005 smaller than a 7.63×39 case. A loaded round’s overall length is 2.26 inches, which fits nicely within a STANAG AR15 magazine, and runs flawlessly with a 6.5 Grendel follower installed.
Deviating from Soviet design, the ARC takes on a 30 degree shoulder angle that is common with other American cartridges, like the 6.5 Creedmoor. The ARC also has less case taper than the Soviet case.
Some of the benefits of the ARC case design is that its non-rebated rim feeds well in detachable and internal box magazines. The cartridge and chamber, by Hornady’s own admission, was designed concurrently. It uses the same design method as the 6.5 Creedmoor, which results in excellent and consistent accuracy from one gun to another, load to load. Early testing indicates a 1:7.5 inches twist rate is ideal for stabilizing long bullets in the 6mm ARC.
Performance Comparison
Reviewing the ballistics comparison between the 6mm ARC and a few .308 loads it is evident the smaller cartridge provides some advantages. The ARC firing a 108-grain ELD-Match bullet with a .536 G1 ballistic coefficient at 2,750 fps muzzle velocity stays supersonic to 1,150 yards at sea level.
Fired from the same length 24-inch barrel, a .308 178-grain boat-tail hollow-point with comparable BC and a muzzle velocity of 2,600 fps goes subsonic just beyond 1,000 yards. Other 175- to 178-grain .308 bullets go subsonic at shorter ranges. Delivering a precision pill accurately more than a football field farther than a standard-issue .308 sniper round, what’s not to like?
Ever heard the phrase “ounces make pounds, and pounds make pain”? Launching a 6mm ARC from a weapon platform that weighs 30 percent less than an AR10-sized weapon makes a lot of sense. Carrying more ammo to the fight in the same loadout is an added benefit, too.
6mm ARC Handloader Quest
As of mid-summer 2020, 22 rifle manufacturers had signed on to build 6mm ARC rifles. Even though Hornady offers three loads for the 6mm ARC – 105-grain boat-tail hollow-point, 103-grain ELDX and a 108-grain ELD Match – they also see the wisdom of offering reloading tools and components to feed shooters taking on the new cartridge.
To get a jump on finding handloads, I brought home four boxes of the 108-grain ELD Match loads from the hunt so I could have a source of brass once I found a rifle chambered with the new SAMMI chamber. Wilson Combat was kind enough to provide one of their new Paul Howe Tactical Carbines kitted out with a 6mm ARC barrel and bolt.
Gun Details
The first firearm collaboration between Wilson Combat and renowned author and tactical shooting expert Paul Howe, this weapon combines Wilson Combat build quality and the 30 years of tactical experience that retired Master Sergeant Paul Howe has learned as an operator and trainer. Touted as their ultimate all-around tactical rifle, the first thing you will notice is its striking new Armor-Tuff camouflage finish. This special finish hides well in both urban and rural environments.
This Paul Howe Tactical Carbine uses a match-grade, stainless steel 16-inch barrel with deep lightening flutes and an Accu-Tac flash hider. As it came from the factory, the Wilson Combat TTU fire control group is one of the lightest, most consistent triggers this writer has pulled. This two-stage trigger breaks cleanly at 2 pounds, 12 ounces every time. A 4 ½-pound trigger spring is included, in case you plan to actually deploy the rifle while in harm’s way. For punching paper and ringing steel, the 2 ¾-pound trigger is a dream.
The 6mm ARC barrel is 1:7.5-inch twist, and it is treaded 5/8-24 TPI. It mated up well with an AAC Cyclone direct-thread suppressor, which was used for all testing. The carbine tips the scales less than 7 pounds unloaded and without an optic.
Rifle in hand, I mounted a Trijicon Accupoint 5-20x scope and burned through the 80 rounds of Hornady ammo on hand to provide the brass needed for crafting reloads.
Reloading Data
DISCLAIMER: Any load data presented in this article is at maximum chamber pressure for this particular rifle. Duplicating loads for any other rifle may present dangerously high pressures in your rifle. This information is solely meant as a basis for comparison with published load specifications from companies such as Hornady and Hodgdon.
This rifle was among the first handful of 6mm ARC guns to come out of Wilson Combat. Bill Wilson had one of these first rifles sent down to his Texas ranch to give it a go at the same time I was working up loads on my Tennessee farm. Swapping notes via email while we shot, it made the chore of finding maximum loads for several powders less time consuming.
One of the first things I did for the reloading process was take some case dimension measurements to optimize the cartridge-to-chamber fit. I used a Hornady Bullet Comporator with a 9-33 bushing and a set of digital calipers to measure base to mid-shoulder length on a fired case from this rifle’s chamber. It measured 1.206 inches. I set up the Hornady resizing die in an RCBS Rockchucker press — in service since 1973 — to lightly “cam over” on the shell holder, and the first sized case measured 1.194 inches base to shoulder on the Comporator. Thinking that 0.012-inch shoulder setback was a tad excessive, so I loosened the die incrementally. Final shoulder setback was set at 1.202 inches. A little more tweaking for a tighter cartridge-to-chamber fit was possible, but I though a 0.004 shoulder bump was a good place to start for working up loads.
Once brass was resized, I measured case lengths and got a range between 1.484 to 1.498 inches. All of the brass was trimmed to 1.482 on an RCBS Trim Pro that’s been on my bench for more than a decade. Primed with Federal benchrest small rifle primers, I was all set to start dropping powder and seating bullets in small batches.
Working from list of 11 probable powder choices, Bill reported that he had success with IMR 8208 XBR, while I got the opposite reaction when I tried MR-2000. He was getting sub-MOA groups, while I was lucky to put five shots inside 2 MOA at 100 yards. I emptied the MR-2000 from my powder measure and refilled it with 8208.
I had two Lapua bullets, a Berger and four Hornady .243 bullets to use in my work-ups. Results got better immediately with the powder swap to IMR 8208. A 90-grain Lapua atop 26.1 grains of 8208 put five shots into a 0.903-inch group, and went down range at 2,546 fps. The same charge weight pushing a 90-grain Hornady ELDX sped along at 2,635 fps, but only managed 1.172 inches for five shots.
Going heavier, I found that 25.2 grains of 8208 was maximum for a 109-grain Lapua. The velocity was a tad slow at 2,436 fps, and its best group of 1.715 inches didn’t impress either. Using the same charge weight, I tried a 110-grain Hornady A-Tip. The result was a 0.526-inch group, but velocity was a mere 2,389 fps. The same powder charge of 25.2 grains driving a 108-grain ELD Match resulted in 2,396 fps, and the best group measured 0.921.
I’ve had good luck using TAC in 6.5 Grendel, so I opted to give it a go in the ARC. The max load for Hornady 108-grain ELD Match, 110-grain Hornady A-Tip and 109-grain Lapua was 27.0 grains of TAC before I got ejector swipe on the case head, a sign of excessive pressure. Velocities for the three bullets atop 27.0 grains ran from 2,559 to 2,567 fps on average, but accuracy wasn’t acceptable at 1.5 MOA.
A load of 28.2 grains was the max for 90-grain bullets, with the Lapua posting 2,748 fps and the Hornady ELDX hitting the 2,757 fps mark. The Lapua 90-grainer won out on the accuracy side with a 0.828-inch group.
The next powder tried was Reloader 15. The rifle liked two loads with R15. A Hornady 103-grain ELDX driven by 27.8 grains of powder produced a sub-MOA group. The best combination of bullet and load was 28.7 grains driving a 90-grain Lapua, which produced a 0.799-inch group and a 2,649 fps muzzle velocity.
Not surprising, you will find in the accompanying chart loads capable of ½ to ¾ MOA. Of the 42 load combinations between six powder and seven bullets in this sampling, some fared better than others. Loads that didn’t hold much promise didn’t even make the chart, hence its abbreviated nature.
The Hornady 6mm ARC is a hammer for coyote-sized game, as I learned in Wyoming, and will be a good choice for whitetails next fall. I’ve got a sharp, new JGS Precision Tool 6mm ARC chamber reamer in hand to chamber a new bolt-action. (jgsprecision.com) By the time the leaves turn I should have it ready to take afield.
Check hand loading pricing and availability at Brownells.
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