6mm ARC vs 6.5 Grendel

So, you were about to jump on the 6.5 Grendel bandwagon when you stumbled upon the 6mm ARC. While they are very similar cartridges dimensionally, the 6.5 Grendel and the 6mm ARC are very different in many respects. In this article, we will go over these differences to help make your decision a little easier.

Physical Attributes

When stood side by side, it would be difficult to tell the 6mm ARC and 6.5 Grendel apart without getting a closer look. Although they do not share every dimension, the 6mm ARC largely used the 6.5 Grendel’s dimensions in its design.

Perhaps the most notable dimension shared between each is their 0.441-inch rim diameter. This means both cartridges can be used on the same bolt, so swapping between cartridges usually only requires a barrel change.

Having said that, the largest difference you will find between these cases is the bullet diameters they use. While the 6.5 Grendel uses 6.5 mm or 0.264-inch diameter projectiles, the 6mm ARC uses slightly smaller 6mm or 0.243-inch diameter projectiles.

This smaller diameter allows for much more aerodynamic bullets to be loaded within the same overall cartridge length, which is the primary appeal of the cartridge. This smaller diameter also equates to slightly lighter bullet weights as well.

While the 6.5 Grendel may be loaded with bullets up to 129 grains, the 6mm is typically found with bullet weights up to 108 grains. Heavier bullet weights can be loaded in either cartridge, though their effectiveness begins to diminish within the magazine length restrictions of the AR-15 platform.

Power

Since both cartridges share an almost identical case size, muzzle energy figures should also be almost identical, right? While a reduction in bullet diameter typically results in decreased muzzle energy, the 6.5 Grendel and the 6mm ARC are very evenly matched.

In fact, looking at Hornady’s ELD-M loadings for each of the cartridges, we find that the Hornady Black 6.5 Grendel produces 1,818 ft/lbs. of muzzle energy with a 123-grain bullet, while the Hornady Match 6mm ARC produces 1,813 ft/lbs. of muzzle energy with a 108-grain bullet. Based on these figures, there’s not enough difference to choose one of these cartridges based on muzzle energy.

The primary difference we run into is the velocity at which each of these cartridges launch their respective projectiles. With a 123-grain ELD-M, the 6.5 Grendel has a listed muzzle velocity of 2,580 feet per second. The 6mm ARC, on the other hand, launches a 108-grain ELD-M at a muzzle velocity of 2,750 feet per second.

This 6.6% increase in velocity not only explains why the 6mm ARC produces the same amount of muzzle energy as the 6.5 Grendel, but it’s one of the main factors leading to its superior long-range performance.

Range

When it comes to shooting at longer ranges, both cartridges punch far above what their small sizes would lead you to believe. Having said that, the 6mm ARC is an undeniably more capable cartridge at further ranges.

On top of its higher muzzle velocity, the 6mm ARC typically uses projectiles with much higher ballistic coefficients than the 6.5 Grendel. In fact, the 108-grain ELD-M referenced previously has a G1 ballistic coefficient of 0.536. While the 123-grain ELD-M has a very respectable G1 ballistic coefficient of 0.506, it is far behind the 6mm offering.

Looking at these figures in a ballistic calculator, we see that the 6mm ARC is not only faster than the 6.5 Grendel, but it is much flatter shooting as well. In fact, at 500 yards, the 6mm ARC only drops 54.1 inches compared to the 64.1 inches of drop experienced by the 6.5 Grendel. This equates to just over 18% more drop at 500 yards when comparing the 6.5 Grendel to the ARC.

At 1,000 yards, this difference becomes even larger, with the 6mm ARC dropping 342.1 inches compared to the 413.5 inches of drop experienced by the 6.5 Grendel. This equates to nearly 21% more drop at 1,000 yards when comparing the 6.5 Grendel to the ARC.

So, it’s easy to see that the 6mm ARC is far more efficient than the 6.5 Grendel at nearly any distance past the 300-yard mark, but it also has a much further supersonic range. In fact, the 6mm ARC load referenced has a maximum supersonic range of nearly 1,275 yards (supersonic = approximately 1,135 feet per second or above at sea level).

This translates to a 16% increase over the 6.5 Grendel’s maximum supersonic range of 1,100 yards. Whether or not this means you will be able to hit targets at these ranges will largely depend on the conditions, as these cartridges use lightweight bullets at medium velocities. Still, there is no denying the 6mm ARC’s superior long-range capabilities.

Availability/Options

So, you have been sold on the 6mm ARC to this point, but there is a major drawback we must address. Currently (subject to change in the future), Hornady is the only major manufacturer producing factory-loaded ammo for the cartridge.

Although they manufacture some excellent products, you will be severely limited on the number of options you can buy off the shelf, especially compared to the 6.5 Grendel. We must remember that the 6.5 Grendel has had many years to gather its current following, which has led to several manufacturers producing ammo for the cartridge.

Given time, the 6mm ARC may acquire a similar following as the 6.5 Grendel, which should ultimately lead to more factory offerings. If you’re primarily wishing to reload these cartridges, then this difference becomes less of an issue.

While there are more brands producing brass for the 6.5 Grendel, companies like Starline and Hornady produce some excellent brass for the 6mm ARC. Combined with the large number of bullet offerings in the 6mm/0.243 bore size, the 6mm ARC has a very large number of combinations when it comes to reloading.

For those who only wish to shoot factory ammo, however, the 6.5 Grendel makes much more sense (at least currently).

6mm ARC or 6.5 Grendel?

While the 6mm ARC and the 6.5 Grendel are very similar cartridges when it comes to size, they are ultimately different cartridges in terms of capabilities. So, the question becomes, which one should you get?

Although the 6.5 Grendel is not quite as efficient as the 6mm ARC at longer ranges, it is still very effective at distances most people do not have access to. Paired with its higher popularity, the 6.5 Grendel is the clear choice for those looking for an assortment of factory-loaded offerings.

While the 6mm ARC is not currently as popular as the 6.5 Grendel, it still has some very compelling factory load offerings. Many of these offer far superior trajectories and, ultimately, better long-range performance over the 6.5 Grendel for those with the room to stretch.

Regardless of which cartridge you choose, you will get an extremely efficient and potent cartridge for the AR platform.

--Banana Ballistics