6mm ARC: The Best AR-15 Round?

6mm ARC: The Best AR-15 Round?

The AR-15 is such a diverse rifle. In its standard configuration, users can use an AR-15 lower receiver for several different calibers without any modification. These range from the reliable and always-useful .223 to the practical .300 Blackout, the straight-walled deer hunting .350 Legend, and then a handful of Big Bore calibers that are real thumpers. 

The 6mm Advanced Rifle Cartridge (ARC) is a newcomer to the scene. Made for long-range shots with low recoil and able to marry to the uber-common AR-15 lower, it seems like the perfect caliber. But is it? We’ll let you decide. 

What Is The 6mm ARC?

The 6.5 Grendel was the first AR-15 caliber designed to produce blistering results from the relatively small AR-15 platform. It has done well and will continue to be a high performer. However, using a significantly larger projectile than the .223 will always limit it. 

Hornady split the difference and opted for a 6mm bullet, which is lighter than the Grendel at around 100 grains. A 6mm bullet translates to a .243, which has proven to be highly accurate and is a notorious deer slayer despite the relatively small size. The 6mm ARC offers similar ballistics to the .243 Winchester but in a much smaller cartridge that is readily compatible with the AR-15 pattern rifle.  

What Is The 6mm ARC Good For?

The 6mm ARC was designed as an anti-personnel caliber for a DoD request, but it is much more than that. The concept was to create a better bridge caliber between the 5.56x45mm and the 7.62x51mm. While there are plenty of calibers out there in that in-between phase (most notably and most similar being the 6.5 Grendel and the 6.8 SPC), they all were either on the smaller end to retain the performance profile close to the 5.56 or swollen in diameter and mass to simulate the punch of the 7.62, but losing the range in the process. 

The 6mm ARC is finally the caliber that marries excellent range (1,000+ yards) with a bullet heavy enough to drop medium game at a distance. Here are a few of the features that make the 6mm ARC a great option for your next build or your next rifle:

The 6mm ARC ballistics are substantially better than those of the .223/5.56mm, all while using a heavier bullet. 

Is the 6.5 Grendel the Same as the 6mm ARC?

The answer should be fairly obvious, but we need to address it. If it appears on Google, it’s because somebody asked it.

The 6.5 Grendel uses a significantly larger projectile than the 6mm ARC. To put it in familiar terms, a 6.5mm bullet translates to roughly .264, or almost a .270. The Grendel is pretty heavy, too, with some slugs weighing in over 140 grains. Coming from such a short case, this is a lot of heft. A .270 Winchester projectile is substantially larger than a .223 Remington bullet side-by-side, and it is hard to imagine squeezing that much bullet into a cartridge that is compatible with an AR-15 lower. 

The 6.5 Grendel is a fine caliber, and you should definitely grab an upper receiver to go with your AR-15 collection. But they are capped at around 800 yards just due to physics. You can only push a bullet like the 6.5 Grendel using a small case and a matching powder charge. 

What’s the Effective Range of a 6mm ARC?

Engineers created the 6mm ARC to provide more stopping power and a longer range from the AR-15 platform. It performs better than many larger AR-compatible calibers.

The 6mm ARC is impressively supersonic past 1,000 yards, making it extremely efficient. 

Based on the 6.5 Grendel case, Hornady redesigned the 6mm ARC with a narrower neck for lighter bullets, achieving higher velocity and muzzle energy while retaining effective power.

What’s the Best Barrel Length For a 6mm ARC Upper?

Don’t be afraid of the long boys in this category. The 6mm ARC is the consummate overachiever: it is a screamer that optimizes a long bullet with a short case. Hornady does their testing with a 24” barrel, so who are we to argue? 

Of course, life isn’t always about the most optimum things. You will still have a high-performing caliber if you opt for the traditional 16” AR barrel or somewhere in between, like our 18” and 20” uppers. Both options are great for reaching out to that antelope that has been outpacing you. They are also good choices for a 100-yard chip shot on that Whitetail buck. 

The Hornady 6mm ARC 103 gr ELD-X® Precision Hunter® leaves the muzzle at a smoldering 2,800fps with 1,793ft/lbs of energy and is absolutely smoking along at 100 yards at 2,623fps and 1,573ft/lbs, so put all that medium game on notice. 

Is the 6mm ARC better than 308?

This is an apples versus oranges question. The lightest .308 ammo that Hornady makes is the 125-grain SST®️, while the heaviest 6mm ARC is a 108-grain match. The average .308 projectile is around 150 grains, and while it is a short-action caliber, it is much more powerful than a micro-action. 

Plus, the .308 has been around for a long time and is easily found at all Big Box stores. The 6mm ARC has a long way to go before it has that kind of notoriety (think decades). Either one will serve you well, but they are different things. 

Parting Shots

We are proud to offer 6mm ARC upper receivers to our catalog of fine rifles and building components. The 6mm ARC is a new caliber, but man, does the 6mm caliber have a ton of potential! The 6mm ARC ballistics are incredible, whether you are looking for long-range precision shooting, long-range medium game hunting, or anything where you want substantially more punch and range than the 5.56x45mm can offer but don’t want to deal with a heavier rifle or heavier recoil.