AR-10s are among the most versatile firearms on the market, second perhaps only to the AR-15 itself. They’re available in a slew of different calibers and configurations suitable for everything from long-range precision, to competition, to close-quarters practice.
To make the most of your AR-10 (or AR-308, or whatever other shorthand you prefer for a large-framed AR), you’ll need to match your cartridge to the task at hand. With so many options, though, that can be a tall order. Below, we’ll go over some of the most popular calibers and what tasks they are best suited for.
AR-10 Calibers Review
AR-10s come in a wide variety of calibers ranging from specialized, subsonic-optimized rounds like 8.6 Blackout to long-range powerhouses like .300 WinMag—although the latter starts to stretch the definition of “AR-10,” since it requires specialized receivers.
Most AR-10s tend to gravitate towards the same handful of calibers, though, which is hardly surprising since they tend to be the best suited for the most common applications for the AR-10. While they all have their pros and cons, they are more different than similar, using the same AR-10 upper and lower receivers, and in some cases, even the same magazines.
.308 Winchester/7.62×51
.308 Winchester is the original chambering of the AR-10. In most ways, it’s interchangeable with 7.62×51, to the point that the vast majority of rifles chambered in one can fire the other—though not every 7.62×51 rifle can fire .308. The ballistics are nearly identical with comparable loads, but .308 Winchester tends to have a much greater variety of bullet weights and designs.
This chambering is so common for large-frame ARs that the category is often referred to as AR-308s, since “AR-10” technically refers solely to Armalite rifles. For more information on whether AR-10 and AR-308 are the same thing, you can check out our article on the topic.
.308 Winchester is one of the most versatile rounds available for the AR-10. It’s exceptionally common, which means it has a huge variety of different loads available, each tailored to a different purpose. It’s effective out to 800-1000 yards depending on the specifics of the rifle firing it, can be used to harvest most game animals in the lower 48, and remains relatively controllable even in fairly rapid fire.
Unfortunately, while a very well-rounded jack-of-all-trades cartridge, it’s not a master of any one single application. Though once a popular choice for a DMR rifle, its drop profile and susceptibility to wind drift make it suboptimal for long-range performance, but it’s also not as easy to use at short range as a mid-sized carbine round. If controllable mag dumps are what you’re after, we recommend reading over our article on AR-10 vs. AR-15, as the latter may be better suited.
6.5 Creedmoor
Newer than .308 Winchester but rapidly coming to match it in popularity, the 6.5 Creedmoor is a highly adaptable round that excels in several different roles.
Compared to .308, the 6.5 Creedmoor is faster, lighter, and flatter shooting. It takes advantage of lighter-weight, higher-ballistic coefficient rounds to achieve less drop over the same distance compared to .308, making it an easier and more forgiving round for long-range target practice.
Despite utilizing lighter bullets, the 6.5 Creedmoor still maintains plenty of ballistic energy for hunting most medium-sized game. The high sectional density of its projectiles lends itself well to terminal performance at common hunting ranges, and the flatter trajectory makes holding for range or wind a simpler process.
Additionally, 6.5 Creedmoor benefits from lower levels of recoil compared to .308, making it a perfect cartridge for the budding or novice marksman. Unfortunately, it does still tend to be a bit more expensive than .308, although the gap between the two is closing year by year.
6mm Creedmoor
A faster, flatter version of 6.5 Creedmoor, 6mm Creedmoor is a popular cartridge amongst long-range and PRS competitors. The even lighter, faster bullets used by the 6mm Creedmoor exaggerate the benefits of the 6.5 even further, offering flatter ballistics and even greater wind resistance.
However, this comes at the cost of terminal effectiveness, so it may not be the best choice for hunting. It’s also a less common and more expensive round, so it’s a poor choice for price-conscious users, since the difference in performance compared to the cheaper 6.5 Creedmoor isn’t drastic.
Choosing the Best AR-10 Caliber
Choosing the right caliber for your next AR-10 build or purchase is all about matching the cartridge to the task. Consider the intended role of your rifle—will you be primarily using it for hunting, or target practice? Does your local range allow for fire at 600 yards or more? Do you plan to use your rifle for competitions that require rapid fire at relatively short distances, such as 2- or 3-Gun matches?
All of these questions will factor into which cartridge is most appropriate for you.
Best AR-10 Caliber for Hunting
Many AR-10 calibers are perfectly capable of harvesting game—even 6mm Creedmoor is sufficient for many mid-sized animals, though that’s not its intended use—but the one that stands above the rest is 6.5 Creedmoor.
While .308 Winchester was once the reigning king of hunting cartridges, 6.5 Creedmoor offers several benefits that make it well worth the slight price increase.
Chief among these is its superior ballistics. A 6.5 Creedmoor AR will nearly always deliver less drop and wind drift over the same range as .308 Winchester, which allows for a greater margin of error in your range and wind calls. At normal hunting ranges—generally inside 300 yards at the extreme end of things—the drop on a 6.5 Creedmoor from a standard 22″ AR-10 barrel is negligible and will keep the round inside the vital area.
The same is true for wind drift within reasonable speeds. While the drop and wind drift on a .308 at these distances is not hard to predict or account for, 6.5 Creedmoor makes it that much easier and reduces the chance of a suboptimal hit.
Moreover, 6.5 Creedmoor offers lower recoil, allowing for faster follow-up shots if one is needed. This is particularly valuable for pursuits like predator hunting, where a hunter may need to take multiple shots at a group of animals, rather than a single shot such as with deer hunting.
While 6.5 Creedmoor does tend to be a bit more expensive than .308 Creedmoor generally, when considering specifically cartridges designed for hunting performance, the difference is so small as to be functionally moot. High-quality hunting ammo differs by only a few cents between 6.5 Creedmoor and .308 Winchester, making it well worth the difference.
Best AR-10 Caliber for Long-Range Precision
When looking for the best caliber for any particular purpose, a good place to start is to look at what the pros use. In this case, 6mm Creedmoor is by far the most common of the three among competitive long-range marksmanship disciplines.
6mm Creedmoor offers the best possible ballistics for long-range performance, allowing users to reach targets up to 1400 yards or more. It’s highly resistant to wind drift and offers the lowest recoil, making it an excellent round for those new to the practice and still learning the basics of long-distance marksmanship.
While its terminal ballistics are not ideal for many applications, it’s more than sufficient for punching holes in paper or swinging a steel gong.
Best All-Purpose AR-10 Caliber
If you’re not yet sure what your application for your rifle will be, or if you plan to use it for more than one purpose, you may want to consider an all-purpose cartridge. While this will necessarily involve giving up some optimal performance for each task, it comes with the benefit of much greater versatility.
The best all-around cartridge for an AR-10 is the original .308 Winchester. This old-school titan does just about everything sufficiently, even if there are better rounds for certain niches.
It’s functional in a wide range of barrel lengths and even in some SBR configurations. It suppresses well, is more than capable of hunting most medium-sized game in the continental US, and with a skilled user, can be highly effective at extended ranges.
Moreover, it’s the cheapest of the bunch, making it the most cost-effective to practice or compete with. A skilled, well-practiced user with a suboptimal rifle or cartridge will always outperform a novice with the latest and greatest gear, so it’s a great choice for those interested in investing in their skills.
A .308-caliber AR is an extremely versatile rifle, functional for everything from range practice and competition, to hunting, to long-range precision.
Conclusion
The AR-10 is a highly versatile platform, capable of being adapted to a huge range of uses. By matching your cartridge properly to your application, you can tune your AR-10 for the best possible performance, or build a jack-of-all-trades rifle that’s ready for whatever you throw at it.
Or course, if price is no object and you truly want the best of both optimization and efficiency, you could always outfit a single AR-10 lower receiver with an upper in each of these cartridges.
