AR-10 Calibers For Your Next Build

The AR-10 is the AR-15 platform’s bigger, bolder older brother. While the AR-10 has been around for decades, there are AR-10 calibers that you may not be as familiar with. The platform experienced a surge in popularity that began in the 2010s. This was due in part to the availability of new chamberings for the rifle on the civilian market.

Before the boom, if you were building or buying an AR-10, everyone assumed you were getting a rifle chambered in .308 Winchester. That’s because it was really the only option readily available to civilians on the market. The AR-10 platform was initially chambered in 7.62×51 NATO when Armalite pitched the weapon system to the U.S. Army. However, the Army declined to adopt it as their battle rifle.

We love having options, especially when it comes to rifles. In fact, if you decide to take a deep dive into the AR-10 market, you will run into more than a dozen different calibers. But, too many choices can lead to information overload and make it tough to pick just one caliber. With that in mind, we have done the leg work for you and compiled a list of five of our favorite AR-10 calibers. 

Popular AR-10 Calibers

If you don’t see your favorite AR-10 chambering on our list, that doesn’t mean we think it’s a bad round. We aim to help you narrow your search by highlighting a few top options. When selecting cartridges for our list, we considered factors such as:

• Versatility 
• Ammo availability 
• Parts availability 
• Practicality 
• Build costs

For example, we left the highly capable .500 Auto Max off our list. Although this behemoth of a round is relatively easy to find, it’s expensive. So are the rifles and components designed to withstand the force the .500 Auto Max generates. It is also primarily designed for one purpose, taking down big, dangerous game.  If you love the .500 Auto Max (or some other cartridge that didn’t make our list), build your rifle in that caliber.

That’s the beautiful thing about the firearms world. You can always build or buy another gun. 

Best AR-10 Calibers

With that settled, the AR-10 calibers that made our list include (velocity/energy averages will vary by barrel length): 

.308 Win VS 7.62×51 NATO

Before “that guy” points it out in the comments, yes, the .308 Win and 7.62×51 NATO are separate cartridges. But they are so close that it was worth mentioning them together.  The 7.62×51 NATO cartridge is what the original AR-10 was chambered in, and it remains a perfectly capable round.

This cartridge is excellent for hunting most game and performs exceptionally in self-defense scenarios. It’s also proven itself in combat, with numerous militaries worldwide utilizing it.  The 7.62×51 NATO can be found at gun stores, sporting goods shops, and online ammo depots nationwide. It is also relatively affordable, especially compared to some of the more obscure cartridges out there. 

Its fraternal twin (the non-identical kind), the .308 Win is unquestionably the most common AR-10 chambering, bar none. It is a timeless classic, meaning you can find ammo and components for your rifle practically everywhere. The .308 Win packs enough punch to take down black bears, elk, wild hogs, and, of course, deer. 

Are The .308 Win And 7.62×51 NATO Interchangeable?

Growing up, one of my dad’s favorite sayings was, “Almost only counts with horseshoes and hand grenades.” Though the 7.62×51 versus .308 Win specs are “almost” identical, that “almost” matters. 

So, are these cartridges interchangeable? Yes and no.

If you have an AR-10 chambered in .308 Winchester, you can fire 7.62x51mm NATO rounds from the same platform. But, if you try to fire .308 Win cartridges in certain rifles chambered for 7.62×51, you may run into a headspace issue which could damage the rifle. If you’re unsure, have a local gunsmith inspect the weapon for you before proceeding.

The best approach is to shoot the cartridge your rifle is chambered for from the manufacturer. 

.243 Winchester

Want more punch than you can get out of an AR-15 but don’t want to deal with monstrous recoil? If this sounds like you, the .243 Win might be the ideal cartridge for your AR-10 build. Like the .308, the .243 is a true classic that you can find almost everywhere. 

To be fair, this smaller, lighter cartridge does not offer the same long-range performance or force as the .308 Win. But it has plenty of power for downing mid-sized game like deer or hogs. You can even take out slightly larger animals with a well-placed shot or two. The .243 is a good fit for smaller-framed shooters. It’s also an excellent choice if you like to spend a lot of time at the range and don’t want to leave with a sore shoulder every time you unload a box or two of ammo.

.300 Win Mag

With all the new-fangled hunting rounds out there, it can be easy to overlook tried and true cartridges like the .300 Win Mag. But this time tested cartridge checks all the boxes and then some. There are only a few manufacturers making AR-10 rifles chambered in .300 Win Mag, but as they say, quality over quantity.

Easy to find ammo? Yep. Versatile and practical? Without any doubt. Capable of delivering superb performance in a wide range of applications? Absolutely! In terms of ballistics, .308 Win Mag sits near the top of the long action cartridges. It’s hard to do better until you bump up to .338 Lapua or .50 BMG.

You get the best features and performance of the long-action, without the compromise of extra size and weight. The .300 Win Mag is a personal favorite of mine. It can take down most big game and provides a flat trajectory so you can reach out and touch your target from hundreds of yards away. Does it have a kick? You bet. But with the right rifle setup, glass, and muzzle device, followup shots at distance are achievable. 

AR-10 Calibers: 6.5 Creedmoor

The 6.5 line of cartridges has taken the AR world by storm over the last few years. While the 6.5 Grendel has developed a cult-like following, it is more commonly used in AR-15 platforms rather than AR-10 variants. That’s one of the big reasons we only included the 6.5 Creedmoor on our list. Besides, we just like the ballistics and performance of the 6.5 Creedmoor better.

Think of the 6.5 Grendel as a young athlete who hasn’t quite grown into his frame. The cartridge is sleek and fast but doesn’t pack as much of a wallop.  The 6.5 Creedmoor is a bit more mature.

It offers exceptional long-range accuracy, less recoil than the .308, and outstanding ballistics performance. The .308 Win still beats out the 6.5 Creedmoor regarding kinetic energy. But the 6.5 Creedmoor holds its own and allows you to deliver shot after shot with surgical precision. 

7mm-08 Remington

Efficient is a great word to describe the 7mm-08 Remington cartridge. It’s part of the .308 Win family, only necked down to hold a 7mm bullet. Its case length is a hair longer than the .308 Win cartridge, at 2.035″ in length. In terms of popularity, it’s right behind the .243 Win, with plenty of factory load options. If you’re familiar with the 7x57mm Mauser cartridge, you can expect similar velocities from the same barrel length, with the 7mm-08 having a slight edge.

Hunters like it because of its low recoil and ability to adapt to a variety of terrains. It’s a flat-shooting cartridge that’s just as at home in the dense forest as it is in the low, open plains. Many deer hunters swear by it, and those hunting larger game talk about its abilities with reverential tones. It may not be a “cool kid” like the 6.5mm Creedmoor, but it would be a mistake to not give it a second look. It’s a .30-caliber cartridge with solid performance that excels in a variety of tasks. 

.338 Federal

If hunting big game is your thing, or you want to have the option to take on prey like moose and bear, check out the .338 Federal. This round is based on the .308 Win cartridge but features a larger neck to accept the beefier .338 projectile. The .338 Federal certainly packs more power due to the heavier bullet. But that extra weight will cost you in range.

Generally, you’ll be limited to targets within 300 yards, as the .338 Federal begins dropping like a ton of bricks past that distance.  In addition to hunting bigger game, you can use the .338 Federal to take out wild hogs and deer. This robust cartridge will stop any mid-sized animal in its tracks – provided you hit your mark.

Choosing Your Chambering

Ultimately, this decision boils down to one question “What do you intend to use your rifle for? Here are our recommendations for everyday uses:

Hunting

If you want to fill your freezer, you need a cartridge that will drop your target quickly and humanely. You don’t want to spend your time walking around the woods wondering where your game went. With that in mind, I suggest the .300 Win Mag.  The .300 Win Mag has the power and ballistics performance to put down your medium to large-sized game. It also enables you to precisely deliver your shots, assuming you have outfitted your rifle with a nice optic and dialed it in. 

Self-Defense

When it comes to self-defense, you need to consider two main factors, stopping power and penetration. Ideally, you want a round that hits like a freight train and leaves a large wound cavity so that you can stop a threat in its tracks. However, you don’t want your cartridge to push through your target and end up in your neighbor’s refrigerator.  In light of those considerations, the .308 Win and 7.62×51 NATO are the best options for self-defense. Due to their popularity, plenty of different cartridges are available in these two chamberings, meaning you will have no issues finding reliable self-defense ammo. 

Recreational Ownership

Want to buy or build an AR-10 just because? I’ve been there and can support that enthusiasm toward the Second Amendment.  If you want an AR-10 that is fun to shoot and you can take out to the range often, I recommend the .243 or .308. The .243 has manageable recoil, and the ammo won’t break the bank, meaning you can practice all you want. The .308 has more recoil and is a little more costly, but the ammo is readily available, making it an excellent choice for recreational shooters. 

Competition 

In a competition setting, the 6.5 Creedmoor delivers. It provides world-class accuracy at absurd distances. The 6.5 Creedmoor has a flat trajectory, manageable recoil, and good velocity up to and beyond 1,000 yards. More than a few championship shooters have earned titles thanks to the 6.5 Creedmoor.  If you want to join the competition scene, other 6mm cartridges are also viable options. But, as noted above, the 6.5 Creedmoor outpaces rounds like the 6.5 Grendel in most metrics, including long-range accuracy. 

AR-10 Calibers – You Don’t Have To Pick Just One

One of the AR platform’s many great traits is its versatility and modularity. After you build out the foundation of your AR-10 rifle, you can go back and make modifications later.  For example, you can build your version of the perfect lower, complete with a high-end trigger and ergonomic grip. You can select an upper to match and finish your build with a BCG, barrel, hand guard, and gas tube system. 

But, if you decide to change your caliber, you can always build another complete upper and swap out your existing one in seconds. This versatility allows you to experiment with several chamberings without the cost of building another complete rifle. Of course, you can do that, too. I mean, you can never have too many ARs. Right?