The 6.5 Grendel makes a light but lethal Designated Marksman Rifle.

The 6.5 Grendel flanked by 7.62 and 5.56 NATO. It shoots flatter and drifts less than both.

The 6.5 Grendel excels at light-recoiling,
long-range tactical applications.

AR15/M16/M4 weapons can extend their range, penetration, and lethality by swapping to a 6.5 Grendel upper. M855 with 62gr FMJ and 6.5 Grendel with 123gr Lapua Scenar shown.

6.5 Grendel: The World’s Best Assault Rifle Cartridge

By Stan Crist

In 1892 the U. S. Army adopted its first smokeless-powder small-arms cartridge. Designated the .30 Army, the then-new round was fired in Krag-Jorgensen infantry rifles and cavalry carbines, as well as the multi-barrel, rapid-fire Gatling guns. Thus began the practice of having a single caliber for rifles and machine guns, a practice that continued for half a century.

With the advent of the Second World War, the American military developed and fielded the .30 Carbine round, the world’s first purpose-designed, intermediate-power cartridge to enter service. Although the .30-caliber M1 carbine was originally intended to be a personal defense weapon, augmenting the larger .30-06 rifle and machine-gun round, its minimal weight, compact size, and increased firepower caused the troops to use it as a de facto assault rifle.

That two-caliber small-arms system lasted through the Korean War, at which time the U. S. Army attempted to revert to having a one-caliber system by adopting the 7.62mm NATO cartridge, for use in the M14 rifle and M60 machine gun. Unfortunately, the ammo produced almost as much recoil as the .30-06 it replaced, causing the M14 to have poor controllability in full-auto fire, even in the relatively heavy M14A1 automatic rifle version.

Also, the M14 — which was originally intended to be a “light rifle” — was nearly as heavy as its predecessor, the famed M1 Garand. Because of the weight factor, the Air Force refused to adopt the M14, and in the early 1960s purchased the AR15 with its 5.56mm round, a rifle that was almost as delightfully lightweight as the obsolescent carbines then in its inventory. Not long after that, the Secretary of Defense directed the Army to also buy the AR15 (subsequently dubbed the M16A1) and discontinue acquisition of M14 rifles, thereby forcing the Army back into a two-caliber system that endures to this day.

Is there a way to avoid a two-caliber system? It seems clear that it cannot be done with a full-power 7.62mm round, as the power of the ammunition determines the size and weight of the weapon. The Chinese have recently made a valiant effort to combine low weight with high performance in their 5.8x42 intermediate cartridge, but long-range effectiveness of the 5.8mm round has reportedly been found unsatisfactory for machine gun use. To date, every nation that has adopted intermediate-power ammunition for combat rifles has found it necessary to also retain a full-power cartridge in the inventory for machine guns and sniper rifles.

This long-running conflict between the quest for minimum weight and maximum performance raises the thought, is a one-caliber family of small arms any longer even an achievable goal? Some have suggested that Alexander Arms' 6.5 Grendel cartridge might be a viable answer to that question. To confirm this idea will require taking a look at the desired characteristics of the infantry rifle, machine gun, and sniper rifle, and then see if the 6.5mm round is truly capable of filling those needs.

Some individuals think that performance of 6.5 Grendel (center) is so good that it has the potential to replace not only 5.56mm NATO (left), but 7.62mm NATO (right) as well.

Evaluation Parameters

Infantry rifle. The weapon should have a large magazine capacity, weigh as little as possible, and provide a maximum effective range of at least 500 meters.

Machine gun. Same weight considerations as for the infantry rifle, but with maximum effective range of 1100-1200 meters. Penetration of "hard" targets should be comparable to that of the 7.62 NATO M80 Ball round.

Sniper rifle. Weight of weapon and ammunition is not as important as accuracy and effective range, which should be at least 800 meters.

Ballistic Performance

Perhaps the most logical start point for such an examination is the increased range advantage claimed for 6.5 Grendel. Unfortunately, full metal jacket (FMJ) ammunition in this caliber is not yet available, so any comparison to 5.56mm and 7.62mm NATO Ball would be somewhat hypothetical in nature. However, since Sierra MatchKing bullets are loaded in the 7.62mm ammo used by snipers and 5.56mm ammo of special operations forces (SOF), a comparison with 6.5mm MatchKing loads should be sufficiently “apples to apples” for a useful evaluation of relative performance.

Sierra MatchKing projectiles: (l. to r.) 5.56mm 77-grain, 6.5mm 123-grain, 7.62mm 168-grain.

Ballistic coefficient (BC) is an indicator of how well a projectile retains velocity during its passage through the air. The higher the BC, the slower will be the rate at which the bullet loses velocity during flight, thereby making a correspondingly flatter trajectory. A list of BCs for applicable MatchKing loads is as follows:

5.56mm Mk262 77gr: BC = 0.362

7.62mm M852 168gr: BC = 0.462

7.62mm M118LR 175gr: BC = 0.496

6.5mm Grendel 123gr: BC = 0.510

When launched from a 20-inch barrel, the 6.5mm 123-grain MatchKing actually shoots a bit flatter than the 7.62mm sniper rounds, and its trajectory is considerably better than that of the 5.56mm Mk262. In addition, wind drift of the 6.5mm bullet is likewise superior to the other calibers. What this means is that an accurized version of the M16A4 rifle, chambered in 6.5 Grendel, would be capable of performing the precision-fire missions that are now done with two different weapons and calibers. The Marines employ the 5.56mm squad advanced marksman rifle (SAMR) and the 7.62mm Mk11 semi-auto sniper rifle, while the Army uses the 5.56mm squad designated marksman rifle (SDMR) and the 7.62mm M110 semi-auto sniper system (SASS).

An accurized M16 in 6.5 Grendel would be capable of precision engagements at long distances. (Courtesy of U.S. Marine Corps)

Even when fired from the shorter, 14-inch barrels of the Mk16 combat rifle that the Marines are reportedly evaluating, and the M4A1 carbine that is currently in service, trajectory and wind drift of the 6.5mm MatchKing are nearly as good as for 7.62mm sniper weapons. Because of the superior ballistic efficiency, 6.5mm carbines sacrifice little ability to “reach out and touch someone” compared to their 5.56mm siblings. This is a matter of some importance, since the compact, fast-handling carbines are increasingly being used to replace M16 rifles. As a prime example, the Army decided in 2006 to pure fleet deploying Brigade Combat Teams with M4A1 carbines in “next to deploy” order as they prepare for assignments in Iraq and Afghanistan.

The M4A1 carbine has been the subject of more than a few complaints regarding failures to incapacitate enemy fighters. Conversion to 6.5 Grendel would correct that deficiency, and also increase long range capability. (Courtesy of U.S. Army)

Terminal Effects

The primary mechanism for the lethality of 5.56mm ammo is the fragmentation that results when the bullet impacts soft tissue at high speed. M855 Ball does not attain sufficient velocity from carbine barrels to produce this effect beyond a short distance, so SOF units received approval to use the Mk262 round, a load that Black Hills had been manufacturing for service rifle competition. The 77-grain Sierra MatchKing loaded in Mk262 ammo offers a significant improvement in range and terminal performance, particularly for short-barreled weapons.

As might be expected, bigger MatchKings produce greater fragmentation and correspondingly larger wound cavities. In May 2006 ballistic gelatin tests were conducted for 6.5 Grendel ammunition loaded with 123-grain MatchKings, which penetrated 2.0-2.5 inches before yawing and fragmenting. The gelatin blocks were shot from a distance of 50 yards, using an Alexander Arms Tactical 14.5 carbine. With an impact velocity of 2385 feet per second, maximum penetration was a shade over 16 inches, and maximum permanent cavity diameter was more than 6 inches. The bullet broke apart into multiple small fragments with jacket pieces visible at 11 inches and 13 inches.

Gelatin block hit with a 6.5mm 123-grain Sierra MatchKing shows substantially greater disruption than blocks hit by 5.56mm projectiles.

After seeing the results of these tests, LCDR Gary K. Roberts (who performs terminal ballistics testing for the military) noted that 6.5 Grendel appears to offer outstanding terminal performance from 14.5-inch barrels “that is far superior to any 5.56mm loads.”

Penetration Potential

In urban combat, such as has occurred in Iraq over the last four years, machine guns will often be used to engage enemy personnel behind obstructions such as vehicles and building walls. The intense firefights in Somalia during 1993 first showed all too dramatically that the 5.56 NATO round was deficient at punching through such barriers, an important factor in adoption of the 7.62mm M240B machine gun.

When better penetration or longer range is required, the 7.62mm M240B machine gun is called into action. However, a light machine gun chambered in 6.5mm Grendel may be able to provide comparable "punching power" and effective range, without the weight penalties of the larger caliber weapon and ammunition. (Courtesy of U.S. Army)

The capability of a bullet to penetrate “hard” targets is determined by several factors, including impact velocity, core hardness, jacket toughness, and sectional density. All other factors being equal, a bullet with greater sectional density will have superior penetration capability. The potential of the 6.5 Grendel in this regard was dramatically illustrated during a May 2004 demonstration at the Blackwater training facility. Lapua 6.5mm 144-grain full metal jacket bullets fired from an Alexander Arms rifle punched through a 1.575" thickness of glass armor that was designed to stop 7.62mm M80 Ball.

Lapua’s 6.5mm 144-grain FMJBT bullet (left) exhibited better penetration of armor glass than did 7.62mm 147-grain M80 Ball (right), despite a 400 fps slower muzzle velocity.

This was quite an impressive accomplishment, and indicates that 6.5 Grendel may very well be capable of matching, if not exceeding, the performance of 7.62 NATO against targets taking cover behind trees, walls, cars, etc. However, final conclusions cannot be reached until testing is done with lighter bullets, since 144 grains is widely thought to be excessively heavy for a 6.5 Grendel general purpose combat load. FMJ projectiles of 110-120 grains in weight are said to be in various stages of development, but won’t likely be in production in the near future.

Carry Load

One minor drawback of 6.5 Grendel is the weight of the ammunition, some 30% heavier than that of the 5.56mm Mk262 cartridge. This means that for a basic load of ten magazines (nine in pouches, plus one in the gun), there is a slight increase in the carry load, as well as a decrease in the number of rounds immediately available to the rifleman.

5.56 Mk262: 10 x 30-rd mags = 300 rds @ 11.2 lbs

6.5 Grendel: 10 x 26-rd mags = 260 rds @ 13.6 lbs

Although this difference could conceivably be critical in some isolated instances of sustained combat where resupply is not possible, the reduced quantity of ammunition must necessarily be balanced against the increased per round terminal effects. Lethality, penetration, trajectory, windage, and other factors are likely to be far more important in most “close encounters of the hostile kind.” Superiority of 6.5 Grendel over 5.56 NATO in these areas is so great that it might outweigh the difference in ammo load. Anecdotal reports from Iraq say that often multiple hits are required with 5.56mm to incapacitate an opponent. If use of 6.5mm reduces the number of hits needed to neutralize a threat, the “stored kills” would effectively increase in spite of the reduction in magazine capacity.

Conclusion

The Army had a logistically sound idea in trying to create a one-caliber, small arms system in the 1950s, but the 7.62 NATO cartridge was simply too powerful to be compatible with a lightweight combat rifle. As a result, today we have a two-caliber system with a relatively short-range, low-power 5.56mm cartridge for use in infantry rifles, carbines, and light machine guns, and a long-range, high-power 7.62mm round fired in sniper rifles and medium machine guns.

Can we have it all? That is, can we have a lightweight, fast-handling weapon like an M4 carbine, and still have the long range “punch” of an M14 rifle? Has ammunition technology grown to the point where we don’t have to choose between minimum weight and maximum performance? The answer, in the form of the 6.5 Grendel, seems to be a resounding, “Yes!”

Grendel News

May 23, 2008