6.5 Grendel vs 6.8 SPC

Is the standard old 5.56 NATO just not cutting it for you anymore? Perhaps you’re ready to step up to a more powerful intermediate cartridge but can’t decide between the 6.5 Grendel or the 6.8 SPC. Although these cartridges fill a similar niche role, they offer many differences that can make for a difficult decision. In this article, we will be going over these differences to help make your decision a little easier.

Physical Attributes

When standing beside each other, you probably wouldn't notice much difference between the overall lengths of these cartridges. Although the 6.8 SPC uses a longer case (1.69 inches) than the 6.5 Grendel (1.52 inches), both cartridges are limited to the same overall length requirements of an AR-15 magazine (2.26 inches nominal). The maximum overall case length is where the similarities stop, however, as they do not share any other dimensions in common. In fact, when looking at the cases, you’ll notice that the 6.5 Grendel is wider than the 6.8 SPC. With a 0.441-inch rim diameter, the 6.5 Grendel is 4.5% wider than the 6.8 SPC’s 0.422-inch rim diameter. Even though the 6.5 Grendel is over 1/8 inch shorter than the 6.8 SPC, the wider dimension gives it an almost identical case capacity (though the 6.8 SPC is slightly higher). The variation in rim dimension also means that it is not possible to use the same bolt when swapping between cartridges.

However, the biggest difference between these cartridges is the bullet diameters of each ammo. As its name suggests, the 6.5 Grendel uses 6.5 mm bullets (0.264 inches). Bullets in this diameter typically go up to 160 grains, though the 6.5 Grendel is seldom found loaded with anything above 130 grains—this is primarily due to its relatively small case capacity and its short overall length requirements.

Contrary to what its metric name would lead you to believe, the 6.8 SPC utilizes 0.277-inch diameter bullets just like the 270 Winchester. Unlike the 270 Winchester however, the 6.8 SPC suffers with bullet weights over 120 grains. Much like the 6.5 Grendel, this is primarily due to its limited case capacity, which is severely reduced when long and heavy bullets are seated.

Power

Being that the 6.5 Grendel and the 6.8 SPC are comparable-sized cartridges that play a similar role, you’re probably wondering how they measure in terms of power. Although neither option can compete with the energy figures of 308-sized cartridges, both elevate the AR-15 platform far above what the 223 Remington or the 5.56 NATO are capable of.

Looking at the factory-listed values, the Hornady 120-grain 6.8 SPC SST offering produces 1,612 ft/lbs. at a muzzle velocity of 2,460 feet per second. While this is an impressive figure, the Hornady 123-grain 6.5 Grendel SST offering produces 1,818 ft/lbs. at a muzzle velocity of 2,580 feet per second. This is an increase of 206 ft/lbs. (12.8%) over the 6.8 SPC—which is substantial, but it does not tell the whole story. The 6.8 SPC figures referenced above use a 16-inch barrel while the 6.5 Grendel uses a 24-inch barrel.

When using the same barrel length of 20 inches and the same loads, the 6.8 SPC produced 1,887 ft/lbs. (2,661 feet per second) of muzzle energy and the 6.5 Grendel produced 1,675 ft/lbs. (2,476 feet per second).

So, although the factory-listed values would have you believe otherwise, the 6.8 SPC is actually more powerful than the 6.5 Grendel (at least with the loads referenced).

*Note: 20-inch velocity figures referenced were verified using a Garmin XERO chronograph, though they are only based on a single lot of ammunition for each cartridge. Range figures were gathered using the Hornady Ballistic Calculator with a scope height of 1.5” and a zero distance of 100 yards.

Range

Although the 6.5 Grendel may lose to the 6.8 SPC when it comes to real-world muzzle energy figures, we must address the long-range capabilities of each cartridge. Due to its longer case design and use of wider-diameter projectiles, the 6.8 SPC suffers from bullets with somewhat low ballistic coefficients. The Hornady 120-grain 6.8 SPC SST has a G1 ballistic coefficient of 0.4, whereas the Hornady 123-grain 6.5 Grendel SST has a G1 ballistic coefficient of 0.51. When extrapolating the real-world velocity and energy figures (found in 20-inch barrels) out to 1,000 yards, we notice just how much of a difference the ballistic coefficient makes.

Although the 6.5 Grendel is starting with over 200 ft/lbs. less energy at the muzzle, it retains over 7.5% more energy than the 6.8 SPC does at 500 yards. At 1,000 yards, this difference becomes even larger, with the 6.5 Grendel retaining over 24% more energy than the 6.8 SPC. With a higher muzzle velocity, however, the 6.8 SPC produces a slightly flatter trajectory out to approximately 850 yards. From that point onward, the 6.5 Grendel is flatter shooting, although most of us likely won’t be shooting past that distance on a regular basis.

Popularity

Being that these cartridges are almost exclusively found in the civilian market, it is safe to say that neither will ever reach the massive popularity of the 5.56 NATO or 223 Remington. Regardless, both cartridges are produced by several manufacturers in several different offerings.

Although finding ammunition should not be too much of an issue for either cartridge (under normal circumstances), more and more manufacturers are starting to produce factory-loaded offerings in the 6.5 Grendel. This not only means more availability for the 6.5 Grendel, but it also leads to cheaper and a greater variety of options when compared to the 6.8 SPC. On top of factory-loaded offerings, more manufacturers produce 6.5 Grendel components for those who wish to reload. As mentioned previously, the 6.8 SPC is not very efficient with bullet weights above 120 grains and bullet options can be somewhat limited, especially compared to the vast number of lightweight 0.264-inch bullets.

6.5 Grendel or 6.8 SPC?

Filling a near-identical role, choosing between the 6.5 Grendel and the 6.8 SPC can be difficult. So, which one should you get?

If you’re specifically looking for as much muzzle energy as possible, the 6.8 SPC will be a better choice with most factory loaded offerings. However, you must realize there will not be as many factory loaded offerings, or even as many bullet offerings when compared to the 6.5 Grendel. If you’re looking to shoot long range, the 6.5 Grendel offers many benefits over the 6.8 SPC. Although it loses to the 6.8 SPC on the muzzle, the 6.5 Grendel retains its energy and velocity better due to its higher ballistic coefficient bullets. You will also have far more options (at least currently) when it comes to feeding your 6.5 Grendel.

Regardless of which option you choose, you are getting a great cartridge that significantly elevates the performance of the AR-15 platform.

-- Banana Ballistics