A few years ago it seemed that short, fat magnums were the wave of the future. But as the AR-15 platform began gaining in popularity, and particularly among hunters who appreciated the modularity of the AR-15 system, new calibers have begun to be developed to maximize the potential of cartridges in the AR-15 envelope. With a maximum overall cartridge length of 2.26-2.30”, and a maximum practical case rim diameter of .447” for double-stacked cartridges, that imposes some limitations on cartridge designs. But American firearms companies have proven themselves up to the task.
One of the latest cartridges to hit the market is the 6mm ARC, developed and introduced by Hornady in 2020. The cartridge is essentially a 6.5 Grendel necked down to take 6mm bullets, and the cartridge fills a niche that had been underserved in the market for years.
6mm bullets have long been favorites of competitive shooters at both short and long ranges. Their ballistic performance is often unmatched by anything in their size range, and it isn’t until you move up to large, heavy 7mm, .338”, or .375” match bullets in large cartridges that you find bullets with better ballistic coefficients. But for the longest time, those wanting to shoot 6mm bullets in AR-pattern rifles had a choice between the 6x45 in the AR-15 or more recently the .243 Winchester and 6mm Creedmoor in the AR-10/AR-308 platform, with nothing in between.
There had been several wildcats created by necking the 6.8 SPC down to 6mm, or the 6.5 Grendel, or chambering the 6mm PPC in the AR-15. But the 6mm ARC is the first 6mm AR-15 cartridge with major factory support, taking advantage of the 6mm bullet size as well as new bullets developed by Hornady to maximize performance of 6mm bullets in the AR-15.
According to published load data, the 6mm ARC is capable of pushing a 107-grain Sierra MatchKing bullet to 2,687 feet per second out of a 24” barrel, for 1,715 foot-pounds of muzzle energy. That compares favorably to the 6.5 Grendel, which pushes a 123-grain Sierra MatchKing to 2,508 feet per second, for 1,717 foot-pounds of muzzle energy. By 100 yards the 6mm ARC has already surpassed the Grendel in muzzle energy, 1,501 to 1,497 foot-pounds, and it retains that advantage out to 1,000 yards, with 357 vs. 337 foot-pounds, for a 6% edge.
The 6mm ARC also comes with significantly less drop, 34.8 MOA at 1,000 yards vs. 41.3 for the Grendel. Recoil energy is also 9% lower in the ARC, although it’s over 60% greater than the .223 Remington. But as with the 6mm Creedmoor vs. the 6.5 Creedmoor, the 6mm bullets offer better performance at distance. The difference between the 6mm ARC and the 6.5 Grendel isn’t quite so great as the difference between the two Creedmoor cartridges, however.
As with many cartridges today, ammunition and components are nearly impossible to find. And the 6mm ARC still doesn’t have the benefit of steel-cased ammunition like the 6.5 Grendel does. But because it’s based on the 6.5 Grendel, it should be relatively easy for Russian ammunition manufacturers to begin production of steel-cased 6mm ARC ammunition. Let’s hope that happens soon, to drive the 6mm ARC’s popularity.
If you already own a 6.5 Grendel, the 6mm ARC probably doesn’t offer you enough extra performance to justify switching. Or if you load 6.5mm bullets in other calibers such as 6.5 Swede or 6.5 Creedmoor, you may not want to have to stock an additional bullet size. But if you’re starting from scratch and looking to get a high performance cartridge for the AR-15, the 6mm ARC could be a good choice for you.