Maybe you’re bored with the same old 5.56/.223 AR chambering and want something with a little more pizazz. Or maybe you want a cartridge with more get-up-and-go than standard issue .223/5.56. If you want an AR-15 chambered in something less run-of-the-mill, there are dozens of alternative MSR chamberings available. There should definitely be something out there that will tickle your fancy. However, knowing which cartridges are useful and which are just passing gimmicks can be a tad more complicated than you might think.
We’re here to help you sort the worthy from the worthless. Room here is limited, so there’s no possible way for us to cover every single alternative chambering, especially since brand-new wildcats hit the shooting scene what seems like every other day. In the interest of space (and limited attention spans), we’re going to focus on what we consider the best alternative cartridges for the AR-15.
.22 Nosler is basically a necked down 6.8 SPC case with a rebated rim. The case is approximately 15 percent roomier than the .223 Remington. With more room for powder, these cartridges can push a .22 caliber projectile about 400 fps faster than the standard .223 Remington.
If you want blistering velocities and flat-as-a-pancake trajectories, .22 Nosler is a fine option. It is perfectly capable of punching targets beyond 1,000 yards, and it won’t even break a sweat while doing it.
The case head diameter of .22 Nosler cartridges is the same as .223 Rem (.378 inches), so you won’t have to swap out your bolt face. To transform your boring .223/5.56 AR to .22 Nosler, all you need is a new upper and some 6.8 SPC magazines and you’re good to go.
However, these cartridges don’t come cheap or easy. They are produced only by Nosler, so not only can they put a major strain on your ammo budget, they can sometimes be hard to get your hands on.
Another lightning fast long-range superstar, .224 Valkyrie (like .22 Nosler) was designed off a 6.8 SPC parent case. .224 Valk was developed by Federal specifically to compete with the .22 Nosler. This one pushes slightly heavier projectiles (Valk is designed around the 90-grain Sierra MatchKing), and while it doesn’t quite reach the same feats of speed as the .22 Nosler, it’s a perfectly viable option for 1000-yard targets. Plus, that heavier projectile is more effective on coyotes and prairie dogs. .224 Valkyrie could even make a viable whitetail cartridge when the rifle is held in capable hands.
.224 Valkyrie works best out of a barrel with a fast 1:7 twist rate. If you want to convert your AR-15 to .224 Valk, you’ll need a new barrel, plus a 6.8 SPC bolt and magazines. While you can technically make your .223/5.56 mags work, it can cause feeding issues, so just splurge on the good 6.8 SPC magazines. It will save you some serious headaches in the long run.
.300 AAC Blackout (.300 BLK)
.300 AAC Blackout is easily the most popular AR cartridge outside the standard .223/5.56 chambering. It’s built on a .223 Rem case with a that’s been neck blown out to accommodate a beefier .30 caliber projectile.
What makes the .300 BLK so popular is its ability to shoot subsonic ammo out of a short barrel. .300 BLK actually gives its best performance out of a 9-inch barrel, so keep that in mind if you decide to convert.
.300 BLK is also perfect for suppressed shooting. Attach a suppressor to your AR-15, grab some subsonic ammo, and you’ll enjoy some seriously quiet shooting. In fact, the loudest sound you’ll hear is the clapping of the bolt.
If you want an AR-15 for home defense or one for popping multiple hogs over a bait station, a suppressed AR-15 chambered in .300 BLK is about as close to perfect as it gets.
Making the switch to .300 BLK really couldn’t be easier. All you need is a new barrel. You get to keep your bolt, lower receiver, and your magazines.
If you want to turn your AR-15 into a long-range hunting rifle, 6.5 Grendel may be the best tool for the job. This one is built on the 7.62×39 case (think AK-47), only it’s been necked down to accommodate a .264 caliber (6.5mm) bullet.
6.5mm projectiles have some magnificent ballistic properties. With high sectional density, they are highly aerodynamic, slow to shed velocity, and are less affected by crosswinds than most other projectile designs.
6.5 Grendel is capable of some pretty impressive long-range accuracy, and while it may not outperform .22 Nosler or .224 Valkyrie at extreme distances, it is certainly capable of reaching 1000 yards successfully. Plus, you’ll feel significantly less recoil in the process.
Where 6.5 Grendel outperforms .22 Nosler and .224 Valkyrie is in the hunting arena. This one is perfectly capable of delivering ethical kills on whitetails and other similarly sized game out to 300 yards.
Converting to 6.5 Grendel isn’t easy. You’ll need to replace your barrel and your bolt, and Grendel parts don’t come cheap. Finding proper magazines and affordable ammo can also be a nightmare. However, if you want a high-capacity, long-range deer dropper with minimal recoil, it may be worth the expense and the hassle.
The .458 SOCOMwas developed for Special Forces Task Force Rangers who demanded a round that could penetrate thick cover and pulverize targets on the other side. It is basically a necked down .50 AE (think Desert Eagle) cartridge altered to take a .458 caliber projectile.
This thing uses fast-burning propellants to push super heavy bullets and deliver massive terminal energy. .458 SOCOM packs all that performance into a relatively small package. And, believe it or not, this beast pairs well with short barrels, subsonic ammo, and suppressors.
To make the switch, you’ll need a new upper, barrel, bolt, and magazines. Also, be prepared to fork out some major cash for ammo. The stuff isn’t cheap. However, if you need to pummel targets with massive energy, it’s hard to beat .458 SOCOM.
If you believe “Go big, or go home” are words to live by, you should consider an AR-15 chambered in .50 Beowulf. This massive cartridge packs a big enough punch to stop pretty much anything that runs on legs (or wheels).
The .50 Beowulf cartridge was originally designed to effectively stop vehicles at security checkpoints. This proprietary cartridge from Alexander Arms utilizes a rebated rim sized to match that of 7.62×39mm. Projectiles move slow, but their massive size and weight packs a powerful punch once it arrives at its destination.
If you want to upgrade to walloping .50 Beowulf, you’ll need a new upper receiver, bolt, barrel, and magazines. You should also be prepared to drop a ton of cash on ammo. Each .50 Beowulf cartridge is going to cost you close to two dollars, sometimes more. However, it rarely takes more than one well-placed shot to annihilate whatever target you’re shooting at.
As we mentioned at the beginning of this article, this is not an exhaustive list of alternative cartridges. There are dozens of other valid (and some not so valid) options for your AR-15.
Choosing an alternate chambering for your modern sporting rifle is a highly personal matter. The AR-15 is one of the most versatile weapons on the face of the planet, and the options of alternate cartridges only increases its versatility. Ultimately, you’ll need to choose the cartridge that offers you the best balance of range, accuracy, performance, and availability to meet your individual needs.
Also, there certainly isn’t anything wrong with sticking with the tried and true .223/5.56 chambering. It’s still the most popular cartridge loaded into MSRs around the globe, and for good reason. It’s affordable, capable, and readily available.
And if you're shooting requires more power and range than .223/5.56 can deliver, there’s nothing wrong with opting for an AR-10. Typically chambered for the more powerful and highly accurate .308 Winchester, an AR-10 is like the AR-15's tough older brother. It has the same easy shootability that made everyone fall in love with the MSR, only it packs a healthier dose of stopping power.