It’s no secret that the United States Army wants to ditch the old 5.56x45mm and 7.62x51mm cartridges in favor of a new high-speed 6.8mm cartridge. This effort is receiving maximum support and funding from the highest levels, so it’ll be interesting to see if an effective solution actually emerges.
Given that the testing/trials are currently in progress, my prognosis is the 6.8mm will replace all 7.62mm weapons and all belt-fed 5.56mm weapons. Individual soldier weapons will likely remain in 5.56mm for the reasons listed below.
The first question anybody asks when learning of the Army’s new initiative is, “Why 6.8mm?” Many assume this is a resurrection of the 6.8mm SPC, but it is not. The new 6.8mm cartridge requirement is shrouded in secrecy because the briefing given at the National Defense Industrial Association (where the Army speaks to the firearms industry) was for “limited distribution only.” That means everything in the brief was not for public dissemination. However, various tidbits from a few in-the-know Army officers has shed some light on the subject.
For instance, according to Army Chief of Staff General Mark Milley, this is a weapon (and cartridge) that could defeat any body armor now and any planned body armor that we know of in the future. The details of exactly how much armor needs to be penetrated and at what distance remain a secret.
From the limited information we have been given, we know the Army has developed, manufactured and given the projectile they know that will meet their requirement to the industry to develop ammunition. There is no good explanation on why it has to be a 6.8mm bullet and, when asked, the Army has said, “It’s a secret.” Not only is this frustrating, but it also smacks of BS. There is nothing magical about the 6.8mm diameter, and it does nothing that a 6.5mm or 7mm bullet couldn’t do as well.
My theory is that 6.8mm is the smallest the Army can make the bullet with whatever super-secret penetrator they put inside. I’m a little bent out of shape over this. If they would have just gone to the firearms industry and told the industry they needed a bullet that can do X, I guarantee the folks that make bullets for a living would have done a better job and wouldn’t have saddled us with an oddball caliber that has very limited commercial application.
I further suspect that this might be some odd tip-of-the-hat to the .276 Pederson, a fine cartridge the Army considered adopting after World War I. Had we adopted the .276 Pederson back then, we would likely still be shooting it today.
While the details about the Army’s projectile are still classified, here is my best guess on its potential makeup. First off, I bet it weighs approximately 135 to 140 grains and must travel at velocities close to 3,100 feet per second (fps) from 13- to 16-inch barrels to meet Army needs. The only way to get that kind of performance from those lengths of barrel is to run chamber pressures up around 80,000 to 90,000 pounds per square inch (psi). This would put proof loads over 100,000 psi. That’s a spicy meatball!
High-pressure ammunition is a hotly contested topic, and I’ve been very critical of the concept. I remain critical of anything that raises chamber pressures above 55,000 psi in a direct-impingement firearm. Anything higher than that and the gun quickly beats itself to death.
Pressures exceeding 55,000 psi in rifles designed for high pressure come with some definite advantages and a handful of disadvantages. The biggest advantages of high-pressure ammunition are substantially increased velocities, the option to attain those velocities from much shorter barrels and improved terminal effects.
All-brass cases can’t handle that kind of pressure and can result in ruptured/split cases, primers being blown out of their pockets, or case heads separating from the body. Either way, all that pressure will go somewhere it isn’t wanted.
Clearly, high-pressure ammunition falls into the realm of “new technology,” and under the direction of the Army’s Next Generation Ammunition directives, the Army has chosen three candidates for further development and eventual selection as the next issued round. Here are the three chosen candidates.
SIG Sauer was the first one to commercially offer the benefits of high-pressure ammunition when they unveiled the .277 SIG Fury at SHOT 2020. SIG’s military designation for their cartridge is 6.8x51mm. This round uses a three-piece case that has a steel case head, brass body and a locking washer that mechanically connects the two.
As noted above, the Next Gen Ammunition program for the Army is deliberately vague, so it’s impossible to get exact metrics on targeted pressures, velocities or effective ranges for any of the new cartridges. However, SIG had to get SAAMI approval for the .277 SIG Fury, and those numbers are open source. The company did tell me that the commercial variant is loaded to slightly lower pressure because SAAMI is cautious about approving such high chamber pressures.
The highest approved SAAMI chamber pressure was 65,000 psi., and the .277 SIG Fury has a SAAMI max pressure of 80,000 psi. That pressure pushes a 135-grain bullet out the end of a 16-inch barrel at just over 3,000 fps. Even 140-grain bullets would leave a 16-inch barrel at 2,970-ish fps.
Shorten the barrel to 13 inches and a 135-grain bullet still leaves at just over 2,900-ish fps. Normally, cutting a barrel from 16 to 13 inches sees a much more significant velocity drop, but a higher chamber pressure is more resistant to that problem.
Of the three Army selections made thus far, SIG is the only one available commercially, and it looks like it’ll stay that way for some time. However, getting SAAMI to sign off on 80,000 psi would be no easy task, even though the cartridge case and guns chambered in .277 SIG Fury can easily handle even higher pressures.
My immediate concerns when learning of the high-pressure ammunition were recoil and barrel life. I had the opportunity to fire SIG’s high-pressure ammunition through both their new “Cross” bolt-action rifle and their Next Generation individual rifle submission. The bolt-action rifle has a 16-inch barrel with a muzzlebrake, and the Next Gen rifle had a 13-inch barrel with a suppressor.
The Cross weighs 6.2 pounds and had the same recoil as a braked .308 Winchester. This was my biggest surprise from shooting the .277 SIG Fury. The reason it has less recoil than imagined is the higher pressure makes the brake work more effectively. Just as competitive pistol shooters learned long ago that hot loads make compensators more effective because the higher pressure makes it “compensate” more, the same principle applies for a braked rifle.
With more effective braking comes more pronounced muzzle blast. I’d rate the muzzle blast from a .277 Fury with a 16-inch barrel more than a .308 Win. from the same barrel length but less blast than a .300 Win. Mag. from a braked 24-inch barrel. Bottom line: It’s hard to tell the difference in recoil or blast when comparing the Fury to other centerfire cartridges.
Barrel life at this point is nothing but conjecture. If forced to make an educated guess, I’d say that if barrel life at standard pressure is 2,500 rounds, barrel life at high pressure will likely be 2,000 rounds.
True Velocity & General Dynamics
True Velocity is the newest ammo kid on the block and is leveraging the most modern technology with their Next Gen ammunition candidate. Their submission uses an unusually shaped polymer case to achieve the program’s goals.
Working in polymer allows True Velocity to rapidly and precisely create shapes that are impossible when working in brass and steel. This means they can make cases of any shape, both internally and externally.
When looking at their Next Gen candidate, it’s impossible not to notice the lack of a conventional shoulder and neck. Designers put a lot of material up around the bullet, and when questioned why, they explained that the lack of shape constraints from working in polymer allowed them to greatly increase shear strength and ammunition durability by choosing the new design.
One principle the company is exploring with their submission is how to get the lowest chamber pressures possible while still meeting performance requirements. Their unique case shape and the ability to easily manipulate internal case dimensions allows them an unprecedented degree of freedom.
Another advantage of the polymer case that they can leverage is the light weight. In my mind, this is one of the most important considerations for the Next Generation firearms. It would make no sense to take existing guns out of the military only to replace them with guns and ammunition that are both heavier than their predecessors.
Even though the exact bullet weights cannot be released, True Velocity stated that a basic load of their Next Gen ammunition is the same weight as a basic load of currently issued ammunition. Considering the greatly extended range and improved terminal effects of the high-pressure stuff, that’s a very big deal and one that both True Velocity and the warfighter can celebrate.
Textron & Winchester
The third and final contender is a cartridge designed by Textron and loaded by Winchester. The two came together to collaborate because while Textron has the design savvy, they do not have the manufacturing and loading capacity that Winchester does. The two are a good match.
The Textron/Winchester cartridge uses what’s called a “telescoping case.” The case is called this because the bullet sits inside powder, and it’s all contained inside a plastic cylinder. This replaces the conventional methodology of placing the bullet on top of the powder.
An advantage of this system is the ability to quickly change calibers and bullet weights. Where a heavy-for-caliber bullet might cause issues with overall length for a regular cartridge, it isn’t a problem for the Textron/Winchester team.
A telescoping case also offers a significant weight savings. When compared to the M240 machine gun and a basic load of ammunition, the new Textron machine gun and basic load is 20-percent lighter. Considering a M240 weighs 22 pounds and 900 rounds of ammunition weighs 49 pounds, 20 percent is an 11-pound difference. That’s a big deal.
So where do I stand after delving deep into the world of the Army’s Next Gen Ammunition? I started out thinking the idea was ridiculous and still think the Army is being silly trying to sell us on the magic of the 6.8mm diameter. I’m betting that’s an arbitrary caliber selected more out of convenience than anything else, and we’d all be better served by something standard like a 6mm, 6.5mm, or 7mm.
However, the Army is also onto a really good idea, and high-pressure ammunition definitely needs to be pursued. With no discernable increase in recoil when compared to the larger calibers with only a moderate increase in muzzle blast and a likely minor reduction in barrel life, high-pressure ammunition offers significantly higher muzzle velocities with a corresponding ton of increased terminal effects. I’m sure it’ll do swell on body armor as well.
I think these guns and ammunition should and will likely replace all 5.56mm and 7.62mm belt-fed machine guns in the military. I think any 6.5mm or 7.62mm precision rifle should also be replaced. However, I think the new gun and ammo will still be noticeably heavier and have more recoil than the issued M4 in 5.56mm. The M4 is already really small and light, so it’s going to be tough to beat. My vote is for the M4 to stay and everything else goes. Time will tell if I’m right.