11 Best AR Calibers In 2024

June 24, 2024   |  

The AR rifle platform is a favorite for many American shooters because it’s incredibly versatile and available in a number of calibers useful for target shooting, home defense and hunting.

You can cover the spectrum with an AR, but that still begs the question: What’s the best AR caliber for your situation?

In this article we list the best AR calibers available in 2024, and why they work so well whether you’re looking to take an AR to the range, hunt, or defend your home.

If you can’t wait, the best AR caliber is a .22 Long Rifle. If you want to see the full AR caliber list, keep scrolling.

Our Top 3 AR-15 Caliber Picks

Here are our favorite AR-15 caliber choices:

  1. 22 Long Rifle – Best All-Around AR Caliber
  2. 6.8 SPC – Best AR-15 Caliber for Home Defense
  3. 6.5 Grendel – Best AR-15 Caliber for Long Range

Let’s examine each caliber in-depth, starting with our top pick, to help you choose the best AR caliber for your shooting needs.

22 Long Rifle – Best All Around AR Caliber

If you’re like me, the first shot you ever took was with a 22 Long Rifle. As the most popular round on the planet, the 22 Long Rifle is unquestionably the best AR caliber thanks to its nonexistent recoil, extremely low cost, and high ammo availability.

The greatest benefit of the .22 Long Rifle (or 22 LR for short) in an AR 15 platform is that it allows you to train with your standard 5.56 NATO rifle for a fraction of the cost. Converting an AR-15 to 22 LR only requires a conversion bolt and new magazines, as any AR 5.56 barrel can be used for 22 LR.

This starkly contrasts with converting your AR to other calibers, as these will require a new barrel.

AR-15 22LR conversion bolts and magazines are inexpensive, and 22 LR bulk ammo is dirt cheap and fun to shoot. You can easily spend an entire day firing 500 rounds of 22 LR for approximately 1/5 the cost of the same amount of bulk 5.56. This allows you to get a lot of training with your AR-15 without breaking the bank on ammo costs.

6.8 SPC – Best AR-15 Caliber for Home Defense

The 6.8 SPC makes an excellent choice for home defense, as it was developed specifically for indoor combat and has exceptional short-range terminal ballistics.

Developed in 2004 as a joint operation between Remington Arms, U.S. Special Operations Command (USSOCOM), and the U.S. Army Marksmanship unit, the 6.8 Special Purpose Cartridge (SPC) was designed to increase the terminal performance of the M4 carbine.

The program’s goal was to mimic the stopping power of the 7.62x39mm Soviet round. In general, the 6.8 SPC was successful at accomplishing this task. But due to chamber design issues when Remington first presented their new round to the military, the 6.8 SPC was not adopted by the Armed Forces.

Even though the U.S. military passed on the 6.8 SPC, it isn’t ineffective. On the contrary, the 6.8 SPC is an especially potent short-range cartridge, boasting a 45% increase in kinetic energy compared to a standard 62 grain 5.56 NATO load.

This added kinetic energy makes the 6.8 SPC an excellent choice for your next home defense carbine. It is also a popular deer and hog hunting round within ranges up to 200 yards.

6.5 Grendel – Best AR-15 Caliber for Long-Range

The 6.5 Grendel is an excellent long-range cartridge for the AR-15, as it fires an aerodynamic 6.5mm bullet with a high ballistic coefficient and resultant flat trajectory.

Although it took a little while for the 6.5mm bullet to take hold here in North America, long-distance shooters have become keenly aware of its long-range accuracy. Its incredibly sleek and aerodynamic design makes for a high-speed/low-drag projectile that is ideal for long-range target shooting.

Developed in 2003 by Alexander Arms, the 6.5 Grendel was conceived as an intermediate cartridge that would extend the effective range of AR-15 rifles out past 800 yards. Utilizing the 6.5 Creedmoor’s same higher ballistic coefficient 0.264” diameter bullets, the 6.5 Grendel can maintain MOA-level accuracy and supersonic velocities out to 1,200 yards with half the recoil of the 308 Winchester.

6.5 Creedmoor – Most Accurate AR Caliber

If you don’t mind stepping up to a larger and heavier AR-10 rifle, then you can witness dramatically improved ballistic performance: precisely why competitive shooters often reach for the 6.5 Creedmoor.

The 6.5 Creedmoor is the cartridge that single-handedly started the 6.5mm love fest in North America. Introduced by Hornady in 2007, the 6.5 Creedmoor was co-developed by renowned marksman Dennis DeMille and Hornady senior ballistician Dave Emary. The two produced a cartridge that boasts low recoil, a flatter trajectory than the 308 Win, and relatively accessible 1,000-yard shots. Extremely tight tolerances in the chamber throat design make the Creedmoor one of the most inherently accurate out-of-the-box rounds available in the market today.

Combining the accuracy and lower recoil of the 6.5 Creedmoor with the semi-automatic capability of the AR-10 makes for a potent long-range target rifle.

300 AAC Blackout – Best AR Pistol Caliber

If you’re looking to build or buy an AR pistol and want a cartridge that delivers optimal performance out of a short barrel, look no further than the 300 Blackout.

Developed in 2010 by Robert Silvers and Advanced Armament Company (later acquired by Remington), the 300 Blackout increases the caliber of the AR-15 rifle to 0.308” while maintaining standard NATO mags.

To put it simply, the 300 BLK is a 223 Rem case that has had its mouth widened to seat a .30 cal bullet. This allows the 300 BLK to fit in standard AR mags and maintain their normal 30-round capacity. It also means that you do not need to purchase a new bolt to fire 300 Blackout, as the base diameter of the case is unchanged from 5.56. Although the mags and bolt remain unchanged from a standard AR-15, a new barrel is required to perform a conversion.

The 300 Blackout was designed to achieve full powder burn in a 9-inch barrel, which is why it’s so often favored for short-barreled rifle (SBR) and AR pistol builds. The 300 BLK is available in supersonic and subsonic factory loads, making it an extremely versatile round. Supersonic loads work well for target shooting, long-range engagements, and whitetail hunting. Subsonic rounds are ideal for use with a suppressor, giving them excellent short-range stopping power accompanied by a report that won’t deafen you indoors.

6mm ARC – Best Overall AR Caliber For Hunting

A relative newcomer to the shooting scene, the 6mm ARC cartridge fires a 0.243” diameter bullet that is indisputably effective on varmints, antelope, coyotes and whitetail deer. It covers a wide breadth and depth of hunting capabilities, which makes it the best multipurpose AR-15 hunting cartridge on the market.

The 6mm Advanced Rifle Cartridge (ARC) was introduced by Hornady in 2020, making it the youngest round on our top 13 list. It was developed at the behest of the United States Department of Defense (DoD) for its multipurpose combat rifle program.

Designed by necking down a 6.5 Grendel case to accept a 6mm bullet, the 6mm ARC requires a bolt, barrel, and new magazines to convert from a standard AR-15. It provides shooters with improved ballistics over the 6.5 Grendel, mostly due to its higher muzzle velocity.

Capable of launching a 103 grain ELD-X at a velocity of 2,800 fps (with 1,792 ft-lbs of kinetic energy), the 6mm ARC is a flat-shooting, hard-hitting round that is more than capable of dispatching virtually any critter plaguing your property (short of bears and elk, which aren’t known to plague all that much anyway).

Groundhogs, coyotes, and deer stand no chance against this hotrod, making it a jack-of-all-trades hunting cartridge that mimics the 243 Winchester in an accessible AR platform.

22 Nosler – Best AR Caliber for Varmint Hunting

The 22 Nosler makes an amazing choice for varmint hunting due to its high velocity, flat trajectory, and lower recoil compared to other intermediate cartridges.

Ever wonder what it would be like to get 22-250 Remington velocities in a standard AR-15? The 22 Nosler nearly accomplishes this thanks to a 25% increase in case capacity when compared to 5.56 NATO. According to Nosler’s website, this capacity increase leads to a 14% higher muzzle velocity and a 30% increase in kinetic energy.

You will need a new barrel for the 22 Nosler. But thanks to its rebated rim, it is compatible with a standard AR-15 bolt.

Debuted at SHOT Show 2017, the 22 Nosler was the fastest AR-15 cartridge of its time, boasting velocities normally reserved for bolt-action cartridges like the 220 Swift and 22-250 Rem. To put this into perspective, a 22 Nosler can launch a 55 grain projectile at 3,500 fps – compared to 3,680 fps for a 22-250.

For varmint hunting, lightweight projectiles with high muzzle velocity are preferred. The 22 Nosler delivers this in spades.

308 Winchester – Best Caliber for Big Game Hunting

The tried-and-true 308 Winchester is virtually identical to the 7.62×51 – i.e. the cartridge the AR-10 was designed around. An 308 Win AR-10 is an excellent tool for taking down whitetail, black bear, and even the mighty elk.

Developed in the 1950s to replace the aging 30-06 Springfield, the 308 Winchester has remained the go-to round for designated marksmen, snipers and machine gunners since its release. The 308 Win has also cut its teeth in the backwoods, and is the favored large game hunting cartridge among many outdoorsmen.

With seemingly unending bullet and load variations, there is a 308 Win for every possible hunting scenario. It is our pick for best big game hunting cartridge for an AR-10 rifle.

450 Bushmaster – Best AR-15 Cartridge for Whitetail

If you want to go deer hunting in North America and plan to use an AR-15, then the 450 Bushmaster’s superior stopping power, range and bullet selection will all prove great companions on your journey.

We now come to the “thumper rounds” – a term coined by the late great Lt. Col. Jeff Cooper. These cartridges are larger than 40 caliber and more than capable of taking down a whitetail deer in a single shot from an AR-15.

“Thumper” rounds get their name from the sensation you will feel in your shoulder upon firing them. In other words, they are all high-recoil cartridges.

Developed for deer hunting across multiple states and territories, the 450 Bushmaster uses a straight-walled case to comply with hunting ammo restrictions in several Midwest states including Indiana, Michigan and Illinois.

The 450 Bushmaster is manufactured by multiple ammo companies. It’s not ubiquitous, but it is readily available. It is also the only thumper round on this list that is SAAMI certified. For a conversion, you’ll need a new barrel, bolt, and single-stack magazine follower (the 450 Bushmaster can utilize standard AR magazines so long as the follower is replaced).

Capable of pushing a 250 grain SST at 2,200 fps with 2,700 ft-lbs of kinetic energy, the 450 Bushmaster is more than capable of taking down a whitetail within 200-250 yards, thus making it our top choice for deer hunting with an AR-15.

458 SOCOM – Best AR Caliber for Hog Hunting

The 458 SOCOM is another thumper round that makes an excellent hog-hunting cartridge. Its ridiculously high muzzle energy and fast follow-up shot capability make it ideal for this task.

There’s no denying that the 458 has made a name for itself with whitetail hunters and elk enthusiasts alike, but hog hunting is where the 458 really shines.

The ability to take fast follow-up shots with a hard-hitting round like the 458 makes it perfect for engaging multiple targets or making second shots on tough game like hogs. Feral pigs have become an inordinately large problem in the southern United States, as a herd of hogs can easily destroy an entire field in a single night. More than a few golf courses have been ruined by roving bands of swine as well.

Ammo availability is one of the few downsides to the 458 SOCOM. Since it is not SAAMI certified, only custom ammo manufacturers currently supply it. Handloading easily remedies this problem, as multiple manufacturers offer 458 SOCOM component bullets (such as the show-stopping 300 grain TTSX by Barnes).

Like the 450 Bushmaster, converting to a 458 SOCOM requires a new bolt, barrel, and single-stack magazine follower. The 458 SOCOM’s bottle-neck design allows for more reliable feeding and higher case capacity than straight-walled cartridge designs of similar size.

The 458 SOCOM is exceptionally effective for self-defense. Take care that close-range shots could result in over-penetration. Although expanding bullets cannot eliminate this risk, they do reduce it, which is why they are an absolute must for home-defense.

Its relative scarcity aside, the 458 SOCOM is an all-around excellent cartridge, and unparalleled when it comes to slaying feral pigs in rapid succession.

50 Beowulf – Best Big Bore AR Cartridge for Security

We saved the biggest for last. The 50 Beowulf fires the heaviest and widest projectiles in our top 13 best AR cartridges list. Developed for checkpoint security and firing through automotive glass, the 50 Beowulf is a powerful .50 cal round that delivers magnum-level terminal performance in the compact and lightweight AR-15 platform.

The 50 Beowulf is Alexander Arms’ second cartridge on our top 13, with the 6.5 Grendel being the first. Designed around an elongated rebated rim 50 Action Express (50 AE) case, the 50 Beowulf brings massive power to the AR platform by firing high-momentul 300 to 400 grain bullets that are not easily deflected by vehicle glass or body panels.

To put this into perspective, the 50 Beowulf has similar ballistic properties as black powder versions of the 45-70 Government – one of the rounds that nearly led to the extinction of the American Buffalo.

A lot of focus has been placed on the 50 Beowulf for its tactical applications. It has also become popular as a sporting round owing to its efficacy on whitetail within 150 yards.

Like the 458 SOCOM, 50 Beowulf ammo can be scarce. Alexander Arms is the primary manufacturer. Reloading can really help alleviate this restriction and allow you to customize your 50 Beowulf ammo to your specific shooting needs.

If you’re looking for a big-bore AR-15 rifle cartridge that is exceptional at close-range engagements, you cannot go wrong with the 50 Beowulf!

Continue reading more of the top picks for AR calibers here.

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About Post Author

Sam Jacobs

Sam Jacobs is the lead writer and chief historian at Ammo.com. Work from Ammo.com's Resistance Library has been featured by USA Today, Reason, Bloomberg's Business Week, Zero Hedge, The Guardian, and National Review as well as many other prominent news and alt-news publications. Sam grew up in a working-class suburb in New England. He has lived in the EU, so has spent a lot of time in countries that don’t value gun freedom. He currently lives off-grid with his wife and kid back in the U.S.

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