The Best (And Most Popular) AR-15 Calibers [2024]

With dozens of calibers available for it, the AR-15 has become one of the most popular rifles in America. But with so many options, picking any one cartridge can seem overwhelming -- so, here are our the top picks for various tasks: All-purpose, long-range, personal defense, subsonic/suppressed fire, and more.

Best All-Purpose Caliber: 5.56/.223

Specifications

• Bullet Diameter: 0.224 (5.7mm)
• Case Length: 1.76" (44.7mm)
• Overall Length: 2.26" (57.4mm)
• Case Capacity: 28.5 gr. H20
• Max Pressure: 62,366 PSI
• Optimal Twist Rate: 1:7 or 1:8
• Common Weights: 55 - 90 grains
• Muzzle Velocity: 3,260 FPS (55-grain), 2,600 FPS (90-grain)

In spite of all the new calibers now found in dozens of rifle configurations, 5.56 NATO and .223 Remington remain the two most popular and generally best "all-purpose" rounds for the AR-15. This fact holes true for a few reasons:

Power, accuracy, and range.

The 5.56 and .223 cartridges remain capable rounds when it comes to stopping power and accuracy at distance. Either round remains supersonic out to 500 yards, with tight shot groups easily achieved at up to 300 yards. Energy is still impressive at this distance, too, affording around 2,000 ft-lbs. of force.

Plenty of hunters rely on 5.56 and .223 for White Tail hunting, and it remains one of the most popular calibers on the market for personal defense. If you're a new shooters practicing the fundamentals of marksmanship, few rounds provide an easier learning curve, too.

5.56 and .223 provide low bullet drop up to 200 yards, with modest felt recoil.

Affordability.

Ammo's gotten expensive over the past few years, but 5.56 and .223 remain generally affordable: A 20-round box of 5.56 NATO average around  $12 to $14, or roughly $0.60 to $0.70 cents per round. Bump up to a 500- or 1,000-round bulk box, and you can find a cost per round of about $0.50.

Upgrades and parts availability.

The AR-15's so popular because it's so easy to modify and upgrade -- and no other caliber on the market affords as much customization and parts availability as the 5.56 and .223 rounds. Together they remain the default cartridges found in nearly all AR-15 chambers, making upgrading your trigger, barrel, buffer system, and receivers affordable and easy.

Shop 5.56/.223 rifle kits here.

5.56/.223 uppers in stock!

Best Subsonic Caliber: 300 BLK

Specifications

• Bullet Diameter: 0.308 (7.83mm)
• Case Length: 1.368" (34.7mm)
• Overall Length: 2.26" (57.4mm)
• Case Capacity: 28.5 gr. H20
• Max Pressure: 62,366 PSI
• Optimal Twist Rate: 1:6 to 1:8
• Common Weights: 110 - 150 grains (supersonic), 200 to 260 grains (subsonic)
• Muzzle Velocity: 2,215 FPS (125-grain), 1,010 FPS (220-grain)

Running subsonic rounds through the AR-15 can be a frustrating endeavor: Dialing in the gas system requires some work -- usually, you'll need an adjustable gas block to ensure reliable cycling -- and then you've got to worry about further tuning the rifle to handle a suppressor, or the occasional supersonic load. That is unless you choose 300 BLK.

High supersonic and subsonic performance.

300 BLK (officially .300 AAC Blackout) was designed specifically for the AR-15 for this purpose. It's perfectly capable of running reliably in supersonic and subsonic loads, with or without a suppressor, and you can typically get away without having to make any gas system or buffer changes when swapping between either round.

Fired from a 16" barrel, supersonic 300 BLK provides low drop up to 200 yards, with acceptable hit probability out to 400 yards or more. Most shooters can expect roughly 1.5 MOA within 200 yards, whether firing supers or subs -- more than enough accuracy for what is effectively a .30-caliber bullet strapped to a 5.56 casing.

Acceptable cost.

300 BLK remains relatively affordable in an otherwise expensive .30-cal market, too. Supersonics average between $0.90 and $1.20 per round, while subsonics average about $1.10 to $1.50 per round.

Broad parts compatibility.

Keeping with the theme of customizing the AR-15, 300 Blackout affords plenty of opportunity. Since it's a short-action cartridge, it fits in standard 5.56/.223 receivers, and uses standard AR buffers and gas systems. 300 BLK even fits perfectly in regular 5.56 magazines, with no other modifications beyond a barrel swap required to upgrade an existing rifle to chamber it.

Good defense cartridge.

The 300 BLK excels in a subsonic configuration with a barrel as short as 7", providing plenty of knock-down power and accuracy within 100 yards when chambered in an SBR. It also affords the full 30-round capacity of a standard AR mag, providing all the rounds you'd need in a defense situation.

Coupled with its low muzzle velocity, subsonic 300 BLK is a popular choice for those seeking a personal-defense round.

Build a custom .330 BLK AR-15 here.

Best Short-Action/Long-Range Caliber: 6.5 Grendel

Specifications

• Bullet Diameter: 0.224" (5.7mm)
• Case Length: 1.60" (41mm)
• Overall Length: 2.26" (57.4mm)
• Case Capacity: 34.5 gr. H20
• Max Pressure: 55,000 PSI
• Optimal Twist Rate: 1:7
• Common Weights: 60 - 90 grains
• Muzzle Velocity: 3,460 FPS (60-grain), 2,640 FPS (90-grain)

Gone are the days of building a glass-bedded bolt action with a 26" barrel to shoot long distance. The AR-15's evolved to provide high accuracy at 800 yards or more, and the 6.5 Grendel remains one of the most popular cartridges for the job.

Small cartridge, big performance.

The 6.5 Grendel does handily manage to ring steel at nearly a kilometer, while still fitting inside the AR's 5.56/.223 receivers. For all its accuracy, the 6.5 Grendel is also one of the lightest recoiling cartridges, making it easy to maintain sight picture and point of aim through the trigger squeeze.

In spite of its light punch, 6.5 Grendel retains more energy beyond 500 yards compared to .308 Winchester, making this a popular alternative to the typical AR-10 setup when it comes to long-range performance.

Long-Range Honorable Mention: .224 Valkyrie

Specifications

• Bullet Diameter: 0.264" (6.7mm)
• Case Length: 2.015" (51.2mm)
• Overall Length: 2.80" (71.1mm)
• Case Capacity: 56 gr. H20
• Max Pressure: 62,000 PSI
• Optimal Twist Rate: 1:10
• Common Weights: 125 - 185 grains
• Muzzle Velocity: 3,100 FPS (125-grain), 2,510 FPS (185-grain)

Simply put, .224 Valkyrie will transform your AR-15 into a laser pointer capable of striking steel with effortless precision. Its drop trajectory remains virtually flat out to 500 yards, and it suffers just a fraction of drop at a kilometer when compared to other long-range loads chambered in the AR platform.

This performance is all thanks to its high muzzle velocity. Its impressive ballistic coefficient allows it to remain supersonic out to 1,300 yards. For comparison, 6.5 Grendel drops to subsonic speeds at just over 1,000 yards. Coupled with its small casing and powder load, .224 Valkyrie is an ideal contender for maximizing the long-range performance of your AR-15.

The only reason we don't consider it the best overall long-range cartridge for the AR is simple: It's expensive to run, difficult to find in store and, if you opt to run the lightest and fastest loads to maximize accuracy at distance, it'll burn your barrel out faster than any other round on this list.

Best Hunting Caliber: .308 Winchester

Specifications

• Bullet Diameter: 0.308 (7.83mm)
• Case Length: 1.52" (38.6mm)
• Overall Length: 2.26" (57.5mm)
• Case Capacity: 35 gr. H20
• Max Pressure: 52,000 PSI
• Optimal Twist Rate: 1:8
• Common Weights: 90 - 130 grains
• Muzzle Velocity: 2,880 FPS (90-grain), 2,510 FPS (130-grain)

The .308 Winchester remains one of the most popular game calibers in North America, and that holds doubly true when it's chambered in our favorite tactical rifle. Although it technically requires the platform's bigger, longer .30-caliber receivers, the .308 is still the crowd favorite as the best AR-15 caliber for hunting.

Are there perhaps better hunting cartridges? Perhaps. Although the AR platform's become crowded with new calibers designed for hunting -- including an endless number of larger 6mm loads -- the .308 Winchester remains a go-to hunting round for a few reasons: It's affordable, and available at just about every outdoor sporting goods store and firearm retail outlet in the country.

It's also a default cartridge for many hunting bolt guns, making it an affordable option for keeping consistency across the chambers in your gun safe. The .308 round is also manageable, affording relatively modest recoil -- especially when mitigated by the AR's buffer system -- and it requires a relatively short barrel length for hunting distances, reducing the overall weight of your rifle.

Build a .308 AR here.

Best "Big Bore" Cartridge: .50 Beowulf

Specifications

• Bullet Diameter: 0.50 (12.7mm)
• Case Length: 1.65" (42mm)
• Overall Length: 2.125" (54mm)
• Case Capacity: 65.8 gr. H20
• Max Pressure: 33,000 PSI
• Optimal Twist Rate: 1:20
• Common Weights: 300 - 400 grains
• Muzzle Velocity: 1,870 FPS (300-grain), 1,800 FPS (400-grain)

At a glance, it's almost comical. The .50 Beowulf is, at publication, the physically largest caliber that fits in the AR-15's standard receivers and magazines. That's right -- it loads in regular ole' .223/5.56 magazines in a single-stack configuration, and the .223 receivers barely manage to squeeze through the barrel extension and ejection port.

There are plenty of other "big bore"-ish cartridges available for the AR-15, like .350 and .400 Legend, .450 Bushmaster, and .458 SOCOM, but none have the size, width, and general "X" factor of this proper .50-caliber round. The .50 Beowulf is arguably the best big bore AR-15 caliber because it's surprisingly cheap, too. Alexander Arms -- the official and only manufacturer -- offers bulk ammo purchases averaging a hair over $1.00 per round.

The .50 Beowulf also makes use of the AR's other standard equipment, including the fire control group, bolt carrier (though it requires a custom bolt face), and normal gas tube length and diameter, mid-length being the most popular configuration. You'll also get away with running a 16" barrel, reducing overall length and weight, while maximizing muzzle velocity and energy downrange.

Being a straight-walled cartridge in a single-stack configuration, .50 Beowulf is surprisingly reliable and easy to run, too -- though you'll want a beefy muzzle brake to handle all that powder burn. In spite of its size, the Beowulf is easy to manage for most shooters, affording a "tame" blitz of muzzle energy that won't break your shoulder.