Probably most shooters who build (or buy) AR-15 rifles end up with rear-charging rifles chambered in 5.56x45mm NATO or .223 Remington, which, in terms of ballistic performance, are effectively one cartridge and the same.

And why shouldn’t they? Both of these cartridges are ridiculously cheap, available in bulk everywhere you can buy ammo, produce almost no recoil, and still shoot laser-fast, flat, and hit hard for their size.

You can use them for competition shooting, including long-range shooting, as well as for hunting and defensive applications. But are there better cartridges, especially for some applications? You bet.

One of these, and a newcomer on the market, is the .338 ARC, only recently developed by Hornady Manufacturing, and specifically for AR-15 rifles. Here’s what to know if you’re considering buying an AR with a .338 ARC upper (especially if you want a side-charger).

.338 ARC vs. 5.56 NATO

Hornady Manufacturing recently added the .338 ARC to its ARC line (that’s Advanced Rifle Cartridge), which also includes the 6 ARC and .22 ARC. This one, the .338 ARC, is a big bore option, one that performs well not just supersonically but also with subsonic loads.

The .338 ARC is based off of both the .220 Russian and 6.5 Grendel as parent cases, the latter which was proposed as an alternative to 7.62 NATO for long-range performance. Interestingly, .338 ARC cartridges will fit into a 5.56 AR mag (although they don’t perform well from them, more on that in a minute), despite the fact that if you look at the cartridges next to each other the .338 ARC will utterly dwarf the 5.56.

While the .338 ARC is capable of satisfying supersonic performance, where it really shines is in subsonic loads. The great thing about the cartridge is the amount of power it delivers in subsonic loads, and its lethality at close ranges. Run it suppressed and it shoots like a whisper; the tradeoff is that it drops like something you’ve never seen.

In a nutshell: it hits harder than the 5.56, by quite a bit, offering better stopping power, and it does so with superior subsonic performance.

Being heavy and slow, the bullet is, as you might imagine, hard to stabilize. As a result, very aggressive twist rates are necessary (our .338 ARC uppers come with precision-manufactured Mos-Tek barrels with a 1:5 rate of twist, but more on that in a moment).

Shooters have had lots of problems with this cartridge, granted. Accuracy is hard to dial in, especially with improper twist rate and without proper bolt headspacing. But if you lock these down, you can get a .338 ARC AR that is a tack driver at 100 yards and delivers the sort of power that few other cartridges in this class can match – if any can at all.

A Better .338 ARC Upper

In our .338 ARC uppers (and builds, for that matter) we address some of the shortcomings others have had with this cartridge, and have strategically partnered with Mos-Tek, who has nailed down manufacturing of the best .338 ARC barrels in the industry.

One superior aspect of the design is the .338 ARC barrel, which as stated is a Mos-Tek innovation. These precision-machined barrels feature a 1:5 twist rate that effectively stabilizes these large, heavy bullets, and the bolt has the proper headspacing to eliminate problems with lockup. The bolt is also perfectly matched to the barrel, perpendicular to within.0005” or  5/10 of a 1000th of an inch. It’s more stable, more consistent, stronger, and engenders better accuracy, too.

That’s another thing shooters have had trouble with in respect to the .338 ARC, but our build can produce cloverleafs at 100 yards – which, if you’ve ever shot .338 ARC, may know is no small feat.

We’ve also solved the mag issues some shooters have had with this cartridge. Our .338 ARC rifles come with a mag that’s less likely to have the cartridge hang up on the chamber, for more reliable, consistent, and smoother feeding.

And our .338 ARC upper is a side-charging AR upper with our patented left-side non-reciprocating charging handle, as well as bolt carrier door that allows for easier access to and removal of the BCG; it also, importantly, reduces gassing while running suppressed, which can be a big deal for any of you that intend to throw a can on the front of your .338 ARC rifle.