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Hornady's 6mm ARC vs. The 6.5mm Grendel: Which is Best?

There has been a lot of debate on whether the 6mm ARC or the 6.5 Grendel is the superior cartridge. It's time to pit them head to head to see which cartridge comes out on top.

Hornady's 6mm ARC vs. The 6.5mm Grendel: Which is Best?

Introduced by Hornady in 2020 the 6mm ARC has made quite the name for itself, but can it take on and defeat the 6.5mm Grendel? (Photo courtesy Hornady) 

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The 2004 vintage 6.5mm Grendel is an impressive cartridge which has defied the odds. Introduced by a small AR-15 manufacturer, Alexander Arms, at the same time Remington released their 6.8x43mm Rem Special Purpose Cartridge, most figured the 6.5mm Grendel would be a brief footnote in history and quickly forgotten. Instead, the plucky Grendel stood toe to toe with the giant from Remington and gave better than it got. They battled for years until Hornady made it a SAAMI standard and Wolf Performance Ammunition introduced economical steel case ammunition in 6.5mm Grendel. With that, the Green Giant’s SPC was seemingly vanquished. Today, the 6.5mm Grendel is recognized as a superlative intermediate cartridge which performs well in barrels from 12 to 24 inches. A fantastic whitetail deer, pig, and coyote cartridge it has endeared itself to hunters.

Despite its moderate muzzle velocity, the Grendel outperforms traditional intermediate cartridges such as the 5.45x39mm, 5.56x45mm, .22 Nosler, .224 Valkyrie, 6x45mm, and 7.62x39mm by using efficient projectiles with relatively high ballistic coefficients (BC) and sectional density combined with a good payload. These retain velocity and energy well. However, in 2020, a new challenger appeared on the horizon, Hornady’s 6x38mm Advanced Rifle Cartridge. Like the 6.8x43mm Rem SPC before it, the 6mm ARC was developed for a specialized Department of Defense (DoD) group. The question I and many others have is, “How well does the 6mm ARC stack up against the 6.5mm Grendel? Which is the better choice?”

6mm Advanced Rifle Cartridge

6mm-arc-vs-65-grendel-04
Magazines are the weak-point of both cartridges; this is due to the dimensions of the AR-15 magazine well.

Why exactly does the 6mm ARC exist? What was it designed to do? According to statements from Hornady, a DoD entity requested a cartridge with certain capabilities. We can deduce these as greater effective range and better exterior and terminal ballistics with increased penetration over the 5.56x45mm. Basically, it sounds like they were looking for 7.62x51mm range and penetration but in a 5.56mm sized platform with less recoil and lighter ammunition load. Like the 6.5mm Grendel, the 6mm ARC was specifically designed to fit within the confines of an AR-15 STANAG magazine well. Hornady’s 6mm ARC, is not an entirely new cartridge design. Rather, it is based on the 6.5mm Grendel, which in turn was based upon the old .220 Russian case. The engineers at Hornady examined Pohjoispaa/Alexander’s 6.5mm Grendel cartridge case design, and then made some changes to optimize it for their specific application. So, it does share the same .441-inch diameter case-head with the 6.5mm Grendel, as well as the .220 Russian and 7.62x39mm.

The shoulder though has been moved back to facilitate loading the very-long-for-caliber 6mm projectiles. Shoulder angle is 30 degrees, case length is 1.49 inches, and it has an overall cartridge length of 2.26 inches. Max pressure is a mild 52,000 psi, to ensure a 6mm ARC AR-15 has a long service life. The 6mm ARC also shares the thicker .059-inch rim of the 6.5mm Grendel which is significantly more robust than the .038-inch rim of the 5.56x45mm. This aids reliability. As they have the same case-head diameter, the 6mm ARC utilizes the same AR-15 bolt as the 6.5mm Grendel. These are readily available and of known quality. While the 6.5mm Grendel was designed around .264-inch projectiles running from 95 to 144 grains, the cartridge is really at its best with projectiles weighing from 107 to 123 grains. The 6mm ARC on the other hand is designed around modern .243-inch projectiles running from 103 to 108 grains. It was specifically designed to utilize very long for caliber projectiles with very high ballistic coefficients to enhance exterior ballistics. By using very efficient projectiles, the 6mm ARC, like the 6.5mm Grendel, doesn’t need to chase after muzzle velocity the way a 5.56x45mm does. From an 18-inch 6.5mm Grendel barrel, firing Hornady’s 123-grain Black ELD-M load, I recorded an average muzzle velocity of 2,520 fps. While initial velocity isn’t blistering fast, the efficient projectiles allow it to retain greater velocity down range.

According to Hornady’s ballistic lab, their 6mm ARC 108-grain ELD Match load will average 2,660 fps from a 20-inch barrel, 2,600 fps from an 18-inch barrel, 2,530 fps cutting it back to 16 inches and about 2,350 fps from a short 12-inch tube. While at initial glance, the 12-inch barrel’s velocity looks rather ho-hum, exterior ballistics are actually pretty good compared to traditional intermediate cartridges. This is due to this projectile’s G1 BC of 0.536. This is substantially higher than either a traditional .308-inch 175-grain Matching (G1 .496) or a .224-inch 77-grain MatchKing (G1 .372).

6.5mm Grendel

6mm-arc-vs-65-grendel-02
Since it was introduced in 2004 the 6.5mm Grendel has gone on to impress hunters and competitive shooters alike with its exterior ballistics and terminal performance. (photo courtesy of Hornady)

The 6.5mm Grendel is a proven performer in the hunting field and works very well ringing steel out to about 800 yards. When it comes to hunting, the 6.5mm Grendel has an advantage over the 6mm ARC in that it puts a larger diameter and heavier payload on target. Mark LaRue, the owner of LaRue Tactical, demonstrated the 6.5mm Grendel’s capabilities shortly after its introduction when he poleaxed a big 5x5 elk bull at over 400 yards. He dropped it with one shot. In the years that followed, hunters across the U.S. were delighted by how the cartridge performs on whitetail, coyotes, and pigs.

Compared to the 6mm ARC, the 6.5mm Grendel has a few basic disadvantages. 6.5mm Grendel ammunition weighs slightly more, and it has a heavier recoil impulse. The heavier 6mm match projectiles will have a higher BC and greater sectional density. The 6mm ARC has a velocity advantage when using high BC projectiles for better exterior ballistics and greater retained energy downrange. Depending upon projectile design, the 6mm ARC can have an advantage when it comes to penetrating intermediate barriers as well. When it comes to penetrating intermediate barriers, impact velocity, projectile design, projectile weight, projectile diameter, and sectional density all come into play. A higher velocity, smaller diameter projectile with greater sectional density will have an edge. The surge in popularity of the 6.5mm Grendel was sparked by the introduction of economical steel case ammunition from Russia. With the demise of steel case ammunition, and inflated prices due to years of panic buying and ammo shortages, interest in the 6.5mm Grendel seems to have cooled. It’s a great cartridge, but many shooters are returning to their 5.56x45mm AR-15s for recreational shooting and relegating their 6.5mm Grendels to just hunting.

6mm-arc-vs-65-grendel-03
Accuracy of both cartridges is excellent when teamed with a good rifle. This three-inch plate was hit with a 6.5mm Grendel at 500 yards.

Magazine issues are the only real drawback to the 6.5mm Grendel, and the 6mm ARC will have similar issues. The internal dimensions of the AR-15 magazine well dictate the external dimensions of the magazine. The use of the 6.5mm Grendel base cartridge dictates the internal dimensions of the magazine. There is very little room between the two. Due to this it’s not possible to produce polymer dual-column dual-feed 6mm ARC or 6.5mm Grendel magazines. There simply isn’t enough room. ARC/Grendel magazines are typically produced from thin stainless steel for a reason. Some work great, others give issues. The perfect solution would be what LWRCI did with their SIX8 6.8x43mm Rem SPC project. They changed the magazine well dimensions, made it larger and optimized the magazine for the cartridge. I have long stated this is what the 6.5mm Grendel needs. But no one wants to move away from the STANAG standard. That said, a good 6.5mm Grendel magazine runs well, and magazines have improved since the cartridge was introduced in 2004.

Which is Best?

Which is better the 6mm ARC or 6.5mm Grendel? There is no clear answer, it will depend entirely on what you are using it for. A certain US military unit picked the 6mm ARC over the Grendel for their specific needs. For medium-size game, the 6.5mm Grendel with its heavier and larger diameter payload will have an advantage. Here at Firearms News, I have been impressed by the 6.5mm Grendel while our Digital Editor, Jack Oller, has had great success in the hunting field with the 6mm ARC. It looks like it’s a horse race. What do YOU think?   If you have any thoughts or comments on this article, we’d love to hear them. Email us at FirearmsNews@OutdoorSG.com.




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