5 Best AR-15 Calibers and Cartridges in 2017

The AR-15 is one of the most versatile rifles that money can buy. Its standard 5.56x45mm cartridge is in use worldwide by police and NATO forces, so you know it’s good.

Lately, it seems a popular thing in the gun world to knock the 5.56. But mostly that’s just because people want something new, even if they don’t really need something new.

So, maybe you’re looking for a bigger caliber, something with a little more bang than the 5.56 (pun intended). Never fear, there are some options for you to consider. The most common of these more powerful cartridges are:

  • .300 Blackout
  • 6.5 Grendel
  • 6.8 SPC
  • .458 SOCOM
  • .50 Beowulf
 ProductPriceWhere To Buy
image of .300 AAC Blackout
.300 AAC Blackout
$
image of 6.5 Grendel
6.5 Grendel
$$
image of 6.8 SPC
6.8 SPC
$
image of .458 SOCOM
.458 SOCOM
$
image of .50 Beowulf
.50 Beowulf
$$

Of course, with each of these alternatives, you’ll discover there are both advantages and disadvantages.


What to Consider When Seeking an Alternative AR-15 Caliber

Making the choice to upgrade your AR has consequences and can affect lives in the real world.

It can make you look like an idiot, never mind the damage to your bank account, if you don’t choose the right caliber for the job.

But, what’s the difference between the different cartridges for the AR-15?

There are three basic categories to think about when choosing a cartridge for your AR and these three usually involve some compromises between power, cost, and usefulness.

You should also consider flexibility and availability of rounds (the 5.56, being the most common cartridge, is readily available).

Power

Everyone knows bigger cartridges are more powerful, right? Not necessarily.

The power of a cartridge depends upon two main factors: velocity and penetration. Though these factors are different, they’re still similar, and one affects the other.

Think of velocity like the engine of a car. It’s what gives the bullet the ability to move. Velocity is defined as: “an object is the rate of change of its position with respect to a frame of reference. Velocity is equivalent to the specification of an object’s speed and direction of motion.

Consider these velocities and weights.

image comparing the different velocities of objects

Yeah, I’m not getting math involved here, though velocity can accompany some scary mathematical equations. If you’re into math, you can research numbers like the kinetic energy of a round. If you’re not, suffice it to say that velocity means motion: the bullet moving through the gap between you and a target.

Bullet weight (also called grain or gr, is a unit of measurement) is the ‘transmission’ of the car engine; it’s what gives the round the ability to move (achieve velocity). This is what causes round penetration, and for both hunting or defense, maximum penetration should be your main thought.

Why do these factors matter?

Well, light bullets at high velocities will still lack the penetration of heavier bullets moving at medium velocities. The weight gives the bullet its capability to penetrate the target.

Think of it like this: you wouldn’t drive a semi to work every day, nor would you hook up a sub-compact car to a trailer to haul it. Your power-to-weight ration wouldn’t be sufficient to move the trailer.

So, you can see it’s not exactly easy to define the exact stopping power of any cartridge. There are numerous variables involved, but you don’t have to be a rocket scientist to figure out the basics.

Flexibility

This is an important factor, whether you’re on a budget or not. Of course, no single firearm can do everything, but certain guns can do most things sufficiently well. The AR-15 is one of those flexible guns.

It’s easy enough to upgrade your AR by adding new uppers and mags. Rather than wasting time (and money) getting all the possible options, you should research the available cartridges for the AR so you’re not tempted to purchase too much cartridge for the job you intend for it.

Consider that you’re probably upgrading for home defense, hunting, or competition shooting. You’re probably tempted to show off by getting the strongest round you can find. But, you’ll pay for that in extra materials, not to mention the impact of said round to your body from recoil.

Availability

It’s not a myth that when you purchase a gun, you have to feed it. This is especially true if you plan to do any target shooting; even if your AR is for home defense, you’ll want to stay sharp with it.

And that means shooting it, regularly.

You won’t want to upgrade your AR to a round that’s difficult to find. And you should take into account the cost of the round you plan to upgrade to. The more rare the cartridge, the higher the cost will be.

Consider the struggle to find ammo during a scare, when ammo is in high demand, or when there’s a low supply. Shipping ammo can be banned by states at any time, and once that happens, it can take a lot of time and effort to overturn. California gun owners are well aware of this fact. Buying ammo online has become the best way for many shooters to get their supplies.

None of the alternate AR cartridges are going to replace the 5.56. Costs of the 5.56 have come down, but they’re still the choice of NATO and police forces, so getting the rounds might always be a problem, either in cost or supply.


5 Most Common Alternate AR-15 Calibers

Let’s take a quick look at the common alternate AR rounds and see what kind of changes you’ll need to make to your AR.

Cartridge Cost of Rounds Changes Needed Uses
.300 Blackout Low Barrel Defense, hunting, target shooting
6.8 SPC Low Barrel, bolt, mags Competition, hunting
6.5 Grendel Medium Barrel, bolt, mags Competition, hunting
.458 SOCOM High Barrel and bolt Hunting
.50 Beowulf High Barrel and bolt Hunting

You should also compare ballistics for each of these AR rounds.

Cartridge Velocity Energy Drop @ 300yds Effective Range
.300 Blackout 125 gr@2200fps 1300 ft-lbs -25” 350 yards
6.8 SPC 110 gr@2500fps 1500 ft-lbs -19” 450 yards
6.5 Grendel 120 gr@2450fps 1600 ft-lbs -18” 450 yards
.458 SOCOM 300 gr@1800fps 1800 ft-lbs -53” 200 yards
.50 Beowulf 400gr @ 1800fps 2878 ft-lbs -50” 200 yards

So, let’s take a look at these alternative AR round in greater detail and discuss the pros and cons of each.

1.   .300 AAC Blackout (.300 BLK)

image of the .300 AAC BlackoutThis round was designed as a replacement for the sub-machine gun MP5SD, which shot the same 9mm as pistols. Because it was based on the M4 rifle, it needed to match or exceed the subsonic 9 mil and be as quiet as possible.

Advanced Armament Company (AAC) took a .223 casing, blew it out to a .30 caliber, and filled it with pistol powder. And that’s it!

It’s a juiced-up cartridge for the AR-15 and it requires only a barrel change to make it work. You won’t have to mess with magazines, lower receivers, or bolt carriers. It’s ready to go!

This is the only semi-automatic cartridge to reliably feed both super- and subsonic rounds without an issue.

You can check out some AR uppers for the .300 at Hardened Arms.

Pros and Cons of .330 Blackout

The .300 Blackout has extraordinary performance from a short barrel and its ability to shoot subsonic ammo without a problem is another bonus.

This round was designed for a barrel around 9 inches and reaches about 95% of full potential with that barrel, making it the best cartridge for short barrel rifles and guns with suppressors.

Using subsonic ammo, this is the perfect setup for home defense if you use a suppressor; it renders it hearing safe. This overcomes the problems with over penetration when used in a confined space.

With suppressed rounds, your effectiveness narrows to just 75 yards and they won’t have much get up and go past 250 yards. Past 300 yards, you get excessive bullet drop.

2.   6.5 Grendel

image of the 6.5 GrendelThis round debuted in the summer of 2004 at the Blackwater Training Facility in North Carolina.

It’s a necked-down 7.62×39, the original AK-47 round, creating a .264 caliber that takes advantage of the excellent ballistics of a 6.5mm bullet.

You can take a look at some 6.5 Grendel uppers for the AR at Alexander Arms.

Pros and Cons of the 6.5 Grendel

One advantage of a 6.5mm bore is the high ballistic coefficient and sectional density. Yeah, I promised no math, so take our word for it, these two factors make this round outperform the 7.62 NATO in terminal and exterior ballistics.

It also shoots flatter, stays supersonic for a longer period, penetrates deeper, and has less recoil than the 7.62 NATO.

This may sound like an advertisement, but the numbers back this up. The 6.5 performs best for both competitive shooting and hunting.

As far as home defense, this is an expensive round at $0.90 to $1.20 per bullet on average. It offers zero advantage within 300 yards and it’s difficult to find the AR uppers with shorter than 20 inch barrels, which is what you want in a home defense rifle.

The cons of using this round include the high level of barrel erosion, price of ammunition, and difficulty in finding proper magazines. Basic parts like the bolt and barrel are expensive as well; the bolt alone might cost you more than $300.

The Grendel magazines are an odd, banana shape like those for the AK, which isn’t bad in itself, but they’re awkward with the lower receiver of the AR-15. And the 6.5mm bore can burn out quickly, which isn’t usually a problem because the ammo is expensive and rare.

3. 6.8 SPC

image of the 6.8 SPCThe 6.8 round was developed for the Army’s marksmanship unit. It was intended as a long-range option for the M4 and they wanted a round to work well for light field use along with exhibition shooting.

It was considered along with the .300 Blackout and 6.5 Grendel as a replacement for the 5.56. Though it performed well at ranges over 250 yards, there wasn’t much point for military use, since any military engagement generally occurs at less than the 250-yard mark. Bison Arms makes some 6.8 SPC Uppers for the AR.

Pros and Cons to the 6.8

This is an excellent round for short-range hunting because it goes further than a .300 Blackout and hits harder than the 5.56.

The 6.8 round is .270 caliber bullet at 115 grains and it maxes out at about 2600fps. It has around 40% more energy than a 5.56, but offers extra penetration because of the bullet mass.

You’ll need to change the barrel and bolt and you can even find them in a package deal, but one disadvantage to the 6.8 is the lack of availability in magazines.

4.  .458 SOCOM

image of the 458 SOCOMThe .458 SOCOM was developed for special operations forces to have some serious punch in close quarters battle. It saw some action in the Middle East because it’s such a man stopper and could be easily suppressed.

It beats other big bore AR cartridges because it performs admirably in a short barrel and rounds are readily available. You can look over some .458 SOCOM AR-15 uppers at Wilson Combat.

Pros and Cons of .458 SOCOM

This round is a necked down .50AE (think of the Desert Eagle) that uses a rapid burning powder and a heavy bullet, making it ideal for SBRs and suppressors.

The .458 isn’t like the .300, whose subsonic rounds make it impractical for hunting. Its 350gr slugs can be used to hunt thin-skinned game within 75 yards.

With subsonic ammo, you’ll see performance like a souped-up .45 Colt and with supersonic rounds, you’ll think you’re using a .45-70 wrapped in an AR-15 package deal.

5.  .50 Beowulf

image of the .50 BeowulfThis is the round that started the big bore AR-15 concept. It’s said to have been developed by the same people who designed the 6.5 Grendel for military use in stopping vehicles at checkpoints as an aid to car bomb prevention. Alexander Arms produces .50 Beowulf uppers for the AR-15.

This monster round packs a punch at both ends and empties your wallet in the process. But the rounds are only produced by a few manufacturers and don’t have premium options for performance hunting.

To keep yourself in ammo, you’ll probably have to learn how to reload. If you’d like to try your hand at reloading, check out our Complete Beginner’s Guide to Reloading Ammo.

Pros and Cons of the .50 Beowulf

There’s no real advantage to this round for home defense; it’s just as effective as an M855 5.56 round and is a deep penetrating bullet. Likely, it would fully penetrate a bad guy and keep going.

For hunting, it’s powerful enough to take down anything in North America, but the key is to get close to your target and use bullets that open reliably to dump all its energy in your target.

As mentioned above, ammunition is rare and costly. If you really have your heart set on the .50 Beowulf, then you’d be better off learning how to reload if you want to have ammunition at all times.


Some Cartridges to Avoid

Now that we’ve discussed some excellent options for AR cartridge upgrades, let’s talk a bit about cartridges to avoid, because there are some of those, too.

5.45x39mm

This was Russia’s answer to the 5.56 M16 in battle for the AK-74. It’s been maiming soldiers since the 1970s and has a horrible reputation.

When used by some bad guys in Afghanistan, these rounds blew up or ricocheted when they hit something like a wall. They didn’t penetrate well, nor did they kill efficiently; they were more likely to cause superficial wounds.

Years ago, the market was flooded with this ammunition, but that source has now dried up. Changing your AR to this configuration won’t gain you any benefits, except possibly cheaper ammo. But overall, it gives you a less effective firearm.

7.62x39mm

This true .30 caliber cartridge fires its 120gr bullets at close to 2200fps from a rifle barrel. While this sounds ideal, it’s really not.

It’s a tapered casing and requires an exaggerated, curved magazine and custom lowers to perform well. It also uses a steel cased ammo with a polymer coating; this doesn’t work well in direct impingement weapons that use the gas from a fired round to cycle the action and reload the next round.

This round isn’t any better than the .330 Blackout and you can’t find it in as many loads. It’s also not easily suppressed, so you’re probably better off going to the .300 Blackout.

But if you’re completely sold on the 7.62, make sure to find a custom lower receiver that moves the pistol grip back to accommodate the magazine required.


Final Thoughts

When you’re looking to upgrade your AR-15, you’ll need to consider a compromise between power, cost, and availability of parts and ammunition.

Some AR upgrades come with a high price tag, so you might need to learn about reloading ammo if your heart is set on these cartridges.

In addition, some of these newer cartridges may fade away in the future, so you may end up doing another upgrade if your rounds disappear.

Decide what’s the most important job you’re upgrading for: is it hunting, competition, or home defense?

The answer to this question will get you closer to choosing the right cartridge upgrade for your AR-15.

LEAVE A REPLY

Please enter your comment!
Please enter your name here