Hornady 6mm ARC advanced rifle cartridge, AR-15 cartridge
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It was snowing sideways when this writer broke his first shot with the new Hornady 6mm ARC (Advanced Rifle Cartridge). Hornady’s Neal Emery invited me to Wyoming in February to help a local rancher with an ongoing coyote problem. I also got some trigger time with the hot new cartridge.

Testing the Hornady 6mm ARC

Hornady is on the front edge of ammo innovation. When I got to Wyoming, Emery was a lot more forthcoming about the 6mm ARC than he had been during our conversation at SHOT Show 2020. During the hours we spent together when the dogs weren’t cooperating, I learned that a yet unrevealed DoD entity 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 closer scrutiny clarifies reasoning.

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 AR-15 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 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; this results in excellent and consistent accuracy from one gun to another and 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

advanced rifle cartridge, AR-15 cartridge, 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 a third less? Splendid. Carrying more ammo to the fight in the same loadout? Now we’re talkin’. Starting to see where this is going?

Tuesday, 18 rifle manufacturers signed on to build 6mm ARC rifles. Since I woke up this morning, at least one more has joined the race. I keep watching the mail box for a sharp new JGS Precision Tool 6mm ARC chamber reamer so I can build a new rifle. For more information, please visit Hornady.com.

Expect more on the 6mm ARC in the upcoming 2021 edition of our sister publication, Tactical Life’s Complete Reloading magazine. In the meantime, grab the 2020 edition on OutdoorGroupStore.com.

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