The AR-15 is renowned for its ability to fit different applications, with enthusiasts having a vast range of customizability to suit various roles. Among the platform’s key features is its ability to chamber different calibers. So, what calibers do AR-15s come in?
Despite there being a wide range of options to choose from, two of the most popular calibers are 5.56 NATO and 6.5 Grendel. 5.56 NATO, being the most commonly available chambering, is well-known for its light recoil impulse and accuracy, while 6.5 Grendel does a great job at bridging the gap between intermediate and full-power cartridges, offering superior long-range performance and ballistic energy.
Both cartridges are a solid pick, but they each come with their own specific advantages. Below, we’re looking at both cartridges to see how they compare.
What is 6.5 Grendel and 5.56 NATO?
6.5 Grendel and 5.56 NATO are both incredible intermediate rifle cartridges, but it’s important to understand that they were designed to accommodate different applications.
5.56x45mm is an updated version of the .223 Remington cartridge. While 5.56x45mm was already in use by the U.S. Military, it was still undergoing optimizations, one of which was developed by FN Herstal. Their updated 5.56 variant was designed to fire a heavier 62-grain steel penetrator instead of its original 55-grain bullet. Once this design was finalized, it was adopted and standardized for NATO, hence the name 5.56 NATO. Now, it’s been in use in some capacity by both Military/Law Enforcement Groups and civilians ever since its implementation.
6.5 Grendel is a comparatively newer cartridge designed in the early 2000s. It was created by Bill Alexander, of Alexander Armory, and Janne Pohjoispää, a ballistician for Lapua. It was designed specifically to have a greater effective range and offer greater ballistic energy to help bridge the gap between intermediate and full-power rifle cartridges.
Suitable Applications
In their respective applications, 5.56 NATO and 6.5 Grendel are excellent cartridges. 5.56 NATO is best suited for close to medium range engagements, particularly within 500 yards. Its high velocities and softer recoil impulse make it better suited for rapid follow up shots in dynamic scenarios like competitions, for instance.
6.5 Grendel is an excellent marksmanship cartridge, excelling in long-range applications such as hunting or precision shooting competitions. Capable of retaining its muzzle energy over long distances, 6.5 Grendel far exceeds the effective range of 5.56 NATO, as it’s able to reach out to anywhere from 800 to 1000+ yards depending on the load and rifle setup.
6.5 Grendel vs 5.56 NATO: Ballistics Comparison
6.5 Grendel uses much heavier projectiles than 5.56, with the cartridge usually housing anywhere from a 100- to a 130-grain bullet. Its muzzle energy can exceed 1,800 ft-lbs, easily outclassing 5.56 NATO which tends to hover around 1,200 to 1,300 ft-lbs of energy and uses smaller 55- to 77-grain projectiles.
This significant difference in energy output is mainly due to the casings of each caliber. 6.5 Grendel uses a larger casing, giving it a larger powder charge. This, along with its heavier bullet, gives it exceptional energy retention.
Range and Accuracy Comparison
As far as range and accuracy go, 6.5 Grendel has the advantage. 6.5 Grendel has a higher ballistic coefficient than 5.56 NATO, allowing it to hold a flatter trajectory while delivering a substantial amount of energy downrange.
5.56 NATO has flat trajectories at shorter ranges but experiences greater drop-off past around 500 yards. So, at distances where your standard 5.56 loads would drop off, 6.5 Grendel has way more energy left to give. This isn’t to say that bullet drop is negligible when shooting 6.5 Grendel, but it’s still much easier to reach out beyond the 500-yard line.
Keep in mind that 5.56 CAN exceed its commonly regarded effective range of 500 yards, it’s just a matter of pairing the right load with the right setup. AR-15 builds, such as SPRs (Special Purpose Rifles), were designed around the Mk. 262 load, which used a 77-grain Sierra Matchking bullet. This type of 5.56 ammo could extend the AR-15’s max reach to 750+ yards. While this isn’t as far as what 6.5 Grendel is capable of, it’s still a noticeable increase.
Practical Applications
As we’ve mentioned thus far, 5.56 and 6.5 Grendel have vastly different ballistic characteristics that make them better suited for different tasks. We’ve already gone over how each caliber performs ballistically, but how do they perform in applications such as home defense or hunting?
Home Defense
Comparing the two calibers, 5.56 is the better choice for home defense. 5.56 NATO uses much lighter projectiles, giving your AR-15 a lighter recoil impulse, making it easier to maintain accuracy with rapid fire. There’s also a much wider range of dedicated defensive ammunition available for 5.56 NATO.
One of the primary concerns that needs to be addressed whenever you’re building a home-defense rifle is overpenetration. Overpenetration is when a bullet impacts and passes through a soft target, but still carries over enough kinetic energy to hit another target. If you’re using specialized 5.56 NATO ammo, this is far less likely to occur, but with 6.5 Grendel being much heavier and moving much faster, overpenetration is a critical concern.
Hunting
As far as hunting goes, both calibers are tremendously effective and commonly used by hunters year-round. They each have an expansive lineup of dedicated hunting loads available, but still, they have their differences.
6.5 Grendel offers a considerable amount of muzzle energy, making it an incredibly effective hunting cartridge for large game like deer, elk, and wild boar. 5.56 NATO, in comparison, can be incredibly effective as well. However, it’s better suited for small to medium game, as it lacks the ballistic energy needed for larger game like elk, unless your shot placement is perfect. For deer and smaller game like wild boar and coyotes, it’s perfectly suitable.
As far as range is concerned, unless you’re running a specialty load, 5.56 NATO won’t have the same long-range capabilities as 6.5 Grendel. As we said before, 5.56 NATO is better suited for targets within 500 yards, while 6.5 Grendel can easily range out to distances as far as 800 to 1000+ yards.
6.5 Grendel Accessories
Building a 6.5 Grendel AR-15
With the AR-15 being as modular as it is, it’s more than possible to build one out chambered in 6.5 Grendel. If building an AR is unfamiliar territory for you, there’s essentially two routes you can take. You can either do a complete build from the ground up using the parts of your choice, or you can opt for a complete lower and upper, pairing them together to complete your rifle. If you plan to build out a stripped lower and upper, there are some key factors to consider before you begin building an AR-15 in 6.5 Grendel.
Unlike AR-15 calibers like .300 Blackout, which uses the same BCG and magazines as 5.56 NATO rifles despite using a different barrel, 6.5 Grendel needs its own bolt, barrel, and magazine.
To start, 6.5 Grendel barrels are available in a multitude of lengths and finishes, with Faxon Firearms and Ballistic Advantage being popular manufacturers. They produce a wide assortment of options, with most ranging from 16 to 20 inches in length.
Besides a new barrel, you’ll also need to a new bolt for your BCG. 5.56 NATO and 6.5 Grendel have different cartridge base diameters, making a new bolt necessary. Now, there are two types of bolt faces for 6.5 Grendel, those being type I and type II. The main difference between them is the head-spacing/bolt face depth. Type I bolts have .125-inch head-spacing, while type II bolts use .136-inch head-spacing. The type I bolt came about because of companies cloning the 6.5 Grendel cartridge, while type II bolts were designed specifically for the original 6.5 Grendel specs, making them the ones you should opt for. Nearly all the 6.5 Grendel BCGs you’ll find nowadays are going to be type II, but be sure to double-check when shopping to make sure you’re getting the right one.
As far as magazines go, 6.5 Grendel will not feed properly out of 5.56 NATO magazines. They require a different curvature to feed properly within the magazine. 6.5 Grendel mags aren’t as widely available as 5.56 mags, but they can still be found easily online. Another distinction that separates them from standard AR magazines is their capacities. Most commonly, you’ll find magazines with anywhere from 5 to 25 or 26 rounds.
There are many 6.5 Grendel magazines available from multiple manufacturers, with some popular ones being Duramag, D&H, and E-Lander. If you’re looking for a magazine with a larger capacity, Geissele’s 6mm ARC magazines will also properly feed 6.5 Grendel ammo, and they feature a larger 30-round capacity.
Customization Options
Just like with any AR build, you’ll benefit greatly from the modularity of the platform. Every part can easily be upgraded and swapped out for custom or aftermarket ones, making the AR-15 an incredibly utilitarian rifle that’s capable of being fine-tuned for different purposes. As such, it’s common to see 6.5 Grendel used in SPR and other long-range builds, as the AR-15 is compatible with a plethora of optics and other accessories.
Conclusion
Both 5.56 NATO and 6.5 Grendel are incredible rifle cartridges that pair particularly well with the AR-15. Despite both cartridges being an exceptional choice, it’s important to understand the differences between them before you make any final decisions on picking one over the other.
5.56 NATO excels in close to medium range scenarios, though special long-range loads can extend their maximum effective range. 6.5 Grendel, on the other hand, shines in long-range applications like hunting and precise marksmanship while offering incredible ballistic energy retention in the process.
Understanding these differences plays a crucial role in choosing the right one for your intended purpose. So long as you dedicate some time to research each caliber while also evaluating your needs and preferences, you’ll make the right choice when building your rifle.
