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The Best AR-15 Calibers By Purpose

The Best AR-15 Calibers By Purpose

Posted by 80-Lower.com on Apr 1st 2021

Which AR round should you pick for home defense? For competition? For hunting and general purpose? There are loads of cartridges that now fit in the average black rifle. Picking the right one for your needs is critical. While 5.56 NATO and .223 Remington are great "do-it-all" cartridges, new loads like 9mm, 300 BLK, 6.5 Grendel, and others tend to provide better performance for specific applications. We're covering the best AR calibers by their purpose.

Factors to Consider

The AR-15 can chamber literally dozens of cartridges. We won't be covering most of them here - but that doesn't mean you shouldn't consider others, too. But how do you pick the best round for personal defense, hunting, competition, or general use? There are a few factors to consider:

  • Power
  • Performance
  • Average cost
  • Optimal setup

First, you need to make sure the round you're considering provide adequate power, but not too much. Excessive recoil and needless barrel length will do you no good. That falls in line with performance: How far and how fast does the round travel? For personal defense, you don't want something too high-velocity, or you'll deal with overpenetration. Average cost is important, too. You need to practice, and practice a lot, if you want to "get good" with your AR and the caliber you chamber in it. That means buying a lot of ammo, which can be expensive depending on the round in question. And taking advantage of that range time means making sure your AR-15 is set up correctly, whether that means building a rifle or pistol. You can't shoot a long-range load out of a 5" barrel, and you probably don't want an 18" barrel for a pistol-caliber build, for example. 

With these consideration in mind, let's take a look at what we think are the overall best AR-15 cartridges by purpose. We're covering some of the uses we already mentioned: Home defense and personal protection, close-quarters combat and suppressed fire, general purpose, and long-range shooting.

For Home Defense & Personal Protection

The AR makes a great defense weapon, as long as you pick the right ammunition. Typical centerfire rifle rounds, like the AR's 5.56 and .223, tend to over-penetrate, increasing the risk of collateral damage and unintended injury, even death. Let's compare the best alternative AR rounds for home defense.

First, a disclaimer

Even special-purpose ammo advertised specifically for home defense is likely to tear through the average home's drywall, sheetrock, and wood supports. Finding the right AR caliber for home protection isn't about eliminating this risk, but reducing it as much as possible.

9mm Parabellum (AR-9)

The AR-9, which is essentially an AR-15 with a new type of lower receiver, provides the perfect platform for home defense. These ARs are configured most often as pistols with barrels as short as 4.5". 9mm can be easily sourced as JHP (jacketed hollow point) ammo. JHPs are designed to fragment and tear apart when striking a target or hard surface. Combine these characteristics with the magazine capacity and maneuverability of an AR pistol, and you've got one of the best home defense weapons imaginable.


The 9mm cartridge is heavily favored for self-defense and by law enforcement because of its relatively high power and compact size. With muzzle velocity approaching 1,300 FPS or more, and muzzle energy of up to 450 ft. lbs. (for +P loads), the 9mm is capable of taking down a threat with a single well-placed shot.


Because 9mm is one of the most popular pistol cartridges ever developed, literally hundreds of different loads are available for virtually every application. Coupled with the AR9 lower receiver variant (which can accept any Glock magazines) and an appropriate 9mm upper, you can achieve sub-MOA accuracy at 100 meters or more. JHP ammunition paired with an AR9 pistol makes for a formidable personal defense weapon.

Average cost

Thankfully, 9mm's popularity means that dozens of manufacturers produce tens of millions of rounds per year. Quality JHP ammunition can be purchased for as little as $0.89 per round. Even "match-grade" FMJ loads can be bought for around the same price.

Optimal Setup

Since 9mm is designed for handguns, it uses a quick-burning powder that can take advantage of short barrels. Essentially, the typical 9mm AR is considered "overbuilt" since it's easy to use a barrel as long as 9" to 11". This will afford hyper-accuracy, though an accurate AR9 can be built with a barrel as short as 4.5". No gas system is required since 9mm operates using blowback. An AR9 with a barrel measuring 7" to 8.5" provides the perfect balance of max velocity and accuracy in a short, lightweight configuration, making it perfect for self-defense.

For Tactical and Suppressed Fire

The AR also makes for a great personal defense weapon (PDW), especially in circumstances where you're not so worried about over-penetration or the environment around you. For that, a new centerfire cartridge developed specifically for special operations has become the perfect CQC round:

.300 AAC Blackout

Simply referred to as 300 BLK, this is a "hybrid" cartridge, of sorts. It's made to be fired suppressed and un-suppressed, with subsonic and supersonic variants available. With a correctly configured AR-15, both loads can be fired interchangeably without modifying your AR. The best part is this cartridge works well in short barrels. The optimal barrel length for 300 BLK is around 9" to 11.5". That removes weight and length off your AR, making it easier to control in close quarters without sacrificing accuracy or stopping power.

Supersonic vs. Subsonic

The unique advantage of 300 Blackout is found in its dual functionality: Rounds can be chambered interchangeably, with no modification to the rifle or pistol itself, providing both supersonic and subsonic fires. This provides the distinct advantage of coupling high-velocity and max power with whisper-quiet functionality and adequate stopping power and accuracy at shorter distances whenever it's needed.


For those who employ supersonic loads (78 to 125 grains, or so), muzzle velocities range between 2,200 and 2,800 FPS with muzzle energy remaining consistent at around 1,360 FPS. Subsonic loads trade a little power for suppressed fire, affording about 1,010 to 1,110 FPS and muzzle energy ranging between 450 and 500 ft. lbs. It's important to note that subsonic power is largely dictated by barrel length, here.


Supersonic 300 Blackout can provide ballistic performance quite similar to 7.62x39mm or 5.56 NATO with the right grain weight. With an optimal barrel length (more on that next) providing max velocity, sufficient accuracy can be achieved at 300 meters. Subsonic loads, paired with the right barrel to keep velocity just below 1,125 FPS (anything greater is supersonic), can provide MOA accuracy at 100 meters or more.

Average cost

300 Blackout is still considered a "niche" AR cartridge, but thanks to its relative physical similarity to 5.56 NATO and .223 Remington casings, cost of manufacturing is not high. The average supersonic and subsonic load runs around $1.25 to $1.50 per round, with high-end match, frangible, and tracer ammo running up to $2.00 to $4.00 per round.

Optimal Setup

300 Blackout needs to be configured just right to afford good accuracy and power with both loads, without causing subsonic loads to becoming transonic or supersonic when fired. The optimal barrel length for firing both loads consistently is 9", paired with a pistol-length gas system. A 1:7 or 1:8 twist rate tends to perform well with both loads, with the faster rate favoring subsonics more.

For General Purpose

While some cartridges excel at specific tasks, the AR-15 can still manage every tasks with some general-purpose ammo. A good "do-it-all" cartridge can provide effective stopping power for personal defense and taking American game, while remaining lightweight and easy to maneuver, and while providing an affordable, effective cartridge. Perhaps not surprisingly, the winning cartridge in this case is...

5.56 NATO/.223 Remington

That means investing in a regular ole' AR-15 chambered in 5.56 NATO or .223 Remington. Law enforcement uses 5.56 NATO, the military still uses it, hunters still shoot with both loads, and either one of these rounds can function quite well as a home-defense, close-quarters, medium-range, and general hunting cartridge when required. With high magazine capacity and relatively low recoil, it's easy to stock up on thousands of rounds for just about any occasion. NATO and Remington are the preferred loads for just about every prepper or gun owner investing in a "just-in-case" rifle.


For being such a small cartridge, 5.56 NATO and its commercial variant (.223 Rem) provides a fair bit of power: The 55-grain FMJ load provides around 3,260 FPS and 1,294 ft. lbs. of muzzle velocity and energy. The M855 steel-core penetrator (a 62-grain load) provides around 3,110 FPS and 1,325 ft. lbs. of power at the muzzle. Either cartridge is capable of immediately subduing an active threat or medium-size game.


Typical 55-gr. and 62-gr. loads area capable of providing high accuracy at 300 meters, while match loads paired with a longer barrel can provide good accuracy up to 400 meters or more. Both loads are capable of sub-MOA accuracy within 100 meters with any factory rifle, and even short-barreled AR pistols provide MOA accuracy at the same distance.

Average cost

5.56 NATO and .223 Remington are two of the most vastly produced centerfire cartridges in existence. Through sheer volume, both loads are cheap: Average cost per round is about $0.60, with match loads costing as little as $1.00 to $1.25. Historically, prices have been even lower, with average cost per round as low as $0.25.

Optimal Setup

The optimal barrel length for achieving max velocity and accuracy is 16", which happens to the be the minimum legal length allowed on any rifle. AR pistols tend to perform well with a barrel measuring at least 8.5" to 9.5". The minimum recommended barrel length for any pistol is 7.5". Any shorter, and you run the risk of keyholding (tumbling) rounds.

For Hunting & Long-Range Shooting

While many shooters go for .30-caliber rifles like the AR-10 and LR-308, the AR-15 gets by just fine thanks to new 6.5mm cartridges capable of reaching out to 800 yards, even 1,000 yards with an accurized setup. Best of all, the 6.5 Grendel can fit in the AR-15's short .22-caliber action, requiring nothing more than a new magazine and barrel swap to convert a working rifle.

6.5 Grendel

We're talking about the 6.5 Grendel. It was developed by Alexander Arms to outperform 5.56 NATO and .223 Remington by providing better accuracy and stopping power for hunters chasing American game. It fires a 0.264"-diameter bullet typically weighing 90 to 135 grains, affording high velocity and wind resistance and thus, a high ballistic coefficient.


6.5 Grendel's larger bullet manages to maintain about the same muzzle velocities as 5.56 NATO and .223 Remington: Light 90-grain loads manage 2,800 FPS and 1,658 ft. lbs. while 123-grain match loads manage around 2,650 FPS and 1,917 ft. lbs. Grendel's heavy loads provide about 31% more energy than 5.56's 62-grain loads, making this cartridge highly effective for most American game.


By coupling a long, thin, heavy bullet with ample velocity, 6.5 Grendel maintains a high ballistic coefficient and is capable of providing high accuracy as far as 800 meters in an AR-15 rifle. It is currently one of the most high-performing rounds available in the AR platform, out-shooting just about every other cartridge currently available. A small tradeoff is found in barrel life: 6.5 Grendel tends to have a shorter barrel life than most other loads.

Average cost

The market for Grendel ammo is still relatively small, and this translates into a higher average cost per round. Current availability comes out to between $2.30 and $5.50 per round. As this cartridge becomes more popular in the following years, average cost is expected to decrease.

Optimal Setup

Maintaining that high velocity with the Grendel load means stacking a longer barrel on your AR-15. You'll need a barrel measuring 20" to achieve optimal velocity and accuracy. Generally, a 1:8 twist is favored for handling the spread of available Grendel loads.

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