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6.5mm Grendel: The Round the Military Ought to Have

by J. Guthrie   |  November 16th, 2012 27


After almost two hours of discussing the long, tortured, and circuitous development and production history of the 6.5mm Grendel, I finally came right out and asked developer Bill Alexander if he thought the Grendel would ever get a shot at replacing the much-maligned 5.56x45mm NATO cartridge.

“Who knows?” Alexander asked rhetorically, knowing there is no clear-cut, defined path to adoption by regular U.S. military units. “It’s not about good weapons and ammunition any more, it’s a political game.”

After leaving the British defense industry and setting up shop at Radford Arsenal in Virginia, Alexander spent his time designing rifles and cartridges for Americans, not studying the procurement process.

If there were a clearly defined process, it could be upset at any point by meddlesome politicians, defense department bureaucrats, or the odd general. Despite the vagaries of the military’s equipment selection process, a quick analysis shows that the 6.5 Grendel is a legitimate contender to replace the entire M4/M16A2 family of rifles, including the SDM-R and SAM-R rifles, the M14-based family of enhanced battle/squad designated marksmen rifles, and the M110 sniper/squad designated marksman rifles. And it could be accomplished with two different uppers and loads.

Since it snuck onto the scene back in 2004, the 6.5mm Grendel has quietly built a devoted following of shooters who like to do just about everything with one cartridge that will fit in an AR-15. It has also generated its fair share of controversy, from who actually developed the Grendel to quarrelsome trademark agreements.

The .50 Beowulf was our first project, and then we did another rifle in 5.45x39mm and could not give the bloody things away,” Alexander said. “The Grendel came along in 2003 after kicking the idea along for a couple years. It really started as an amusing wildcat. The .50 was a 200-yard gun at best, and I was looking for something with more legs, something you could hunt whitetails with.”

The original Grendel concept, based on the 6.5mm PPC case, was certainly not the only 6.5mm wildcat floating around, and Bill Alexander certainly was not the only guy working on an AR-compatible cartridge. Arne Brennan’s 6.5mm wildcat was very similar to the Grendel—Alexander and Brennan compared notes on their projects from time to time—and he can be credited with a tremendous amount of development work in the 6.5mm AR arena.

Alexander did finalize the dimensions for what became the Grendel case, chamber, and throat after working closely with ballisticians from Lapua, notably Janne Pohjoispaa.

“From the PPC cartridge we kept the 30-degree shoulder angle, but shortened the neck and increased the neck thickness,” Alexander said. “We also ended up keeping the small primer and flash hole because that’s what Lapua was using in the .220 Russian brass, which is what we made Grendel brass from. After we finalized the dimensions, the Grendel stopped being an interesting wildcat and turned into a production cartridge.”

Alexander trademarked the name and specs soon after so the Grendel would not be bastardized out of existence, a fate that has befallen several other cartridges lacking the backing of a major ammunition manufacturer.

“The first 300 cases were carried over in the suitcases of Lapua reps arriving for the 2004 SHOT Show,” Alexander said. “I started trying loads and got an inkling of what we had. The Grendel was more flexible and shot better than I ever hoped and wasn’t the pain in the butt I thought it would be.”

Quite a few other AR manufacturers soon realized the Grendel’s potential, but the trademark was the source of a lot of gun industry acrimony. All of this is now a moot point—Hornady sponsored the cartridge’s submission to SAAMI early last year, and now the Grendel is a cartridge available to the masses, sort of.

“We have certainly seen our share of boom and bust, but quite a few rifle and ammo companies are starting to realize the Grendel’s potential,” Alexander said.

Other Intermediate Cartridges
What makes the 6.5 Grendel better for general military operations than all the other intermediate AR cartridges? Nothing can match the Grendel’s range. Cartridges such as the 6.8mm SPC and .300 Blackout are 300- or 400-yard cartridges at best. The Grendel is a 500-plus-yard cartridge. Bullets are the key.

“When Remington introduced the 6.8 SPC at SHOT the same year as the Grendel, we thought we were going to get exterminated,” Alexander said. “But they couldn’t have handed it to us on a plate any better. We really only started showing up in magazines and such when writers compared us to the SPC. The results really spoke for themselves. Otherwise no one would have ever heard of us.”

The 6.5mm hits a ballistic sweet spot for optimal bullet flight, much more so than the squat, fat bullets used by other cartridges. Most 6.5mm bullets higher than 100 grains start with ballistic coefficients of more than .400, something a 110-grain 6.8mm bullet (.360 BC) or 125-grain .300 Blackout bullet (.153 BC) could never hope to match.

To its credit, the .300 Blackout is much easier to suppress with 200-grain and up bullets, and it works well in PDW-length uppers. Most importantly, the Blackout uses 5.56mm magazines. The 6.8mm SPC has a little more case taper and is theoretically more reliable, but from an external ballistics standpoint, the Grendel is far superior to both.

The Grendel in Uniform
Alexander had some very simple answers when I asked him what the Grendel would look like in uniform. The entire suite of carbines, standard service rifles, and designated marksmen rifles—and that adds up to dozens of models in two calibers, 5.56×45 and 7.62×51 NATO—could be replaced by just two rifles and two bullet weights.

Despite what’s been said on the Internet, the M4 is one of the most popular infantry arms in U.S. military history, getting pretty favorable marks from combatants. So why would you want to replace it? One of the few complaints has been battlefield lethality, and most of those problems can be attributed to ammunition. The M855 Penetrator, or green tip round, was designed to defeat body armor at extended ranges. A better ammo option for now exists in the 62-grain SOST round among others, but bigger is usually better, especially if it fits in the same compact and reliable rifle. Soldiers are having trouble dominating the battlefield past 300 or 400 yards.

Alexander theorized the perfect replacement would be an M4 chambered in 6.5 Grendel with the same, handy 14.5-inch barrel and 107- to 110-grain FMJ projectiles constructed along the lines of the old Soviet 7N6 or 7N10 penetrator round. According to Alexander’s data, the 107-grain Sierra MatchKing and 108-grain Lapua Scenar cruise along at 2,500 to 2,520 fps out of M4-length barrels and have much improved BCs and mass over any 5.56mm round.

Testing showed Grendel bullets shed an average of 6 fps per inch when dropping from 28 inches down to 20 inches and 23 fps per inch when dropping from 20 to 14.5 inches. While 5.56mm bullets are just that much more ineffective out of shorter barrels, the Grendel’s efficiency and increased mass make it a more efficient killer.

Because of its length and rear weighting, the theoretical 6.5 Grendel general service round would yaw and cause significant wounding at extended ranges or up close. With a BC well above .400—the 108-grain Scenar has a BC of .465—it would crush the 5.56 and extend the average infantryman’s effective range beyond 500 yards. Seeing the target well enough to hit it becomes the issue, not terminal performance.

The squad designated marksman is a Soviet concept, borrowed by the U.S. military in Iraq and Afghanistan. Integrating a soldier or marine with extra training and an accurized, scoped rifle into infantry squads has paid big dividends. The marksmen help direct fires, identify threats, and engage targets well beyond the effective range of infantrymen equipped with standard rifles. The services have used both highly modified M16s and pulled the M14 out of retirement to meet the challenge.

M16 rifles generally were equipped with heavy, 1:8-twist match barrels around 20 inches in length and, when possible, paired with excellent Mk 262 Mod 1 ammo. The 77-grain BTHP has the most stringent accuracy standard of any small arms ammunition in the U.S. military and delivers exceptional battlefield performance. The bullet usually yaws after impact and fragments, causing debilitating wounds. Mk 262 is lacking in the barrier penetration department, construction and mass being the limiting factors.

“Amongst all the scuffling and shouting, the 5.56 is a very good and effective caliber,” Alexander said. “How many .308s win at Camp Perry now? The 5.56 with a correctly constructed bullet is a very useful round, but the 6.5’s big advantage is delivering twice the material and energy to the target and greatly limiting wind drift.”

Most M14 rifles, coated in Cosmoline and stored away in the 1960s, had their wood stocks replaced with modular chassises that more readily accepted optics and other aiming, infrared illumination devices, etc. Accuracy tweaks and optics with a 10X top end were added before shipping overseas. When paired with 175-grain M118LR ammo, infantrymen armed with the M39 Enhanced Marksman Rifle (USMC), MK14 (NSW), or Enhanced Battle Rifle (Army) were good out to 1,000 yards depending on conditions. The 7.62mm round was, and is, obviously more lethal and penetrated barriers better than the 5.56.

The big disadvantages to the M39/EBR are its special ammo (or at least ammo not common to the average rifleman), magazines, and weight.

Retrofitting rifles is expensive and time consuming, and finding spare parts for a rifle that has not been in regular service for 50 years was a challenge at times.

The M110 SASS has been very well received by troops, mostly because of its semiautomatic capability. The fact that it runs almost exactly like its M16 little brother certainly doesn’t hurt. But it is heavy, heavier than the M16 at least, and still has the same oddball magazine and ammo requirements like the M39/EBR.

A DMR rifle in 6.5 Grendel with the right bullet solves most of these problems without giving up much in terms of downrange performance (see the accompanying charts). Alexander suggested an off-shelf solution in the form of Lapua’s 123-grain Scenar HPBT. Out of a 20-inch barrel the bullet would be pushing 2,600 fps with a .527 BC—the M118LR’s 175-grain MK has a BC of .505—so it doesn’t have to start out very fast to be effective downrange. Marksmen also gain five rounds, up to 25 from 20, by going Grendel instead of 7.62.

“Since most DMR rifles are equipped with 20-inch barrels, it makes sense to keep that length,” Alexander said.

“That barrel length generates enough velocity to stay supersonic out to 1,200 yards with the Scenar.”

Like the M16-based DMR rifles, both the Grendel infantry carbine and DMR would use the same magazines, same parts, and in a pinch the same ammo. The big advantage is 7.62-like lethality in a lightweight rifle. Grendel carbines and DMR rifles actually weigh a few ounces less than 5.56mm guns because the bore is bigger and there is less barrel steel to tote up the hill. Logistics guys and armorers would probably weep with joy to see the everything-is-different EBRs boxed up and salted away. Infantrymen would appreciate a rifle that is a couple of pounds lighter than the M110.

Alexander pointed out a misconception about the Grendel. Some think the short case’s minimal taper makes it difficult to feed. In reality the case has adequate taper and feeds exceptionally well—even with the green lacquer coating that stops the 5.56. It provides very reliable select fire ability. The magazine is still a weak point for heavy military use, but improvements are being made.

“Probably the biggest penalty would be the extra weight it would take to match a 5.56mm round count,” Alexander said. “Since the Grendel runs at low pressures (MAP is 50,000 psi), steel cases are an option, and that would help negate some of the weight gain.”

What would it take to convert millions and millions of M4 and M16 rifles to 6.5 Grendel? In theory, just a barrel, a bolt, and a magazine. The cartridge produces more recoil than the 5.56, but not so much more that it requires a new buffer or scope/accessory mounts.

“Probably the easiest and least expensive route would be to buy new uppers,” Alexander said. “Sure, you could swap barrels and bolts, but by the time you paid an armorer to do the work, the upper is probably the best route.”

The 14.5-inch upper runs $650 without rail, and the DMR upper runs $820, retail. If the U.S. military took the plunge and switched, these prices would obviously come way down. (A brand-new M4 runs just over $700.) But there is more to it than swapping rifles. All the supporting industries, namely ammunition manufacturers, would have to spin up production lines. And there is the issue of all that 5.56 and 7.62 ammo and the accompanying magazines sitting in storage depots around the world. A wholesale swap to 6.5 Grendel would cost billions of dollars.

History Repeating Itself
The British Army’s Land Pattern Musket, or Brown Bess, debuted in 1722 and was the infantry’s primary rifle for more than 100 years. There were dozens, if not hundreds, of incremental changes to improve its performance. But for the most part, its flintlock ignition and caliber remained unchanged. Ordnance officers felt that a new system that only marginally increased the musket’s battlefield performance simply was not worth the cost.

As it stands, the M16/M4 in 5.56x45mm is a good system that has been greatly improved over its 50-year service life. Sights, ammo, magazines—everything has been upgraded, and the rifle is accurate and reliable. Even though the 6.5 Grendel cartridge is far more lethal and has the potential to completely replace two different calibers and a dozen firearm systems, it still would offer an incremental increase in performance and therefore will probably never be issued to soldiers and marines headed into combat.

The same could have been said about the M16, too, right up until the moment a Colt salesman put one in the hands of General Curtis Lemay.

Alexander would neither confirm nor deny that rifles chambered in 6.5 Grendel had been requested or tested by the U.S. military. And since Alexander is being so tight lipped, only time will tell if the Grendel will ever become the next U.S. military service round.


The 6.5 Grendel (center) has a five-round magazine capacity advantage over the .308/7.62 (right), but gives up five rounds to the .223/5.56 (left).

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