A Green Beret’s thoughts on the great debate: 6.8mm vs. 5.56mm

The Department of Defense conducted trials for a new general-purpose 6.8mm round, something that I think was long overdue. Anytime a new caliber comes up, we see much gnashing of teeth from two separate camps. On the one side is the "good enough for grandpappy at Khe San" crew, who will deride the waste of tax money and preach shot placement.

And on the other will be the "I knew 5.56 was an underpowered poodle shooter round, we should all have 300 Winchester Magnum carbines." Often accompanied by stories of shooting a bad guy 50 times, but he still ran off with the guidon. But just for a moment, let's get our underwear out of a bunch, and take a critical look at 5.56 as a caliber.

The first thing we need to understand is how we got here. Most people already know the story of how the M-16, and its new 5.56 bullet, were first adopted by the Air Force for security forces at airfields. Painful as it is to admit, the Air Force is often smarter than the rest of us. The Army and Marine Corps were having none of it, sticking to the traditional obsession with a .30 caliber bullet. The M1 Garand, chambered in 30.06, won WWII.

New technology in the 1950's allowed the development of .308 Winchester (aka 7.62x51), which in layman's terms is ballistically identical to 30.06, in a shorter case. Add to that the idea of a detachable magazine, and you get the M-14.

The resemblance of an M-14 to an M1 Garand isn't coincidental. John Garand designed the M1, and actually started working on its perceived shortcomings in 1944. Eventually, the M-14 would emerge, which is essentially a .308 caliber, magazine-fed, M1 Garand.

It was everything the Army and Marine Corps ever wanted, while notably, allies such as NATO did not. (The British were pushing hard for a .280, which we will address further in a bit.) In 1957 it was announced the M-14 would replace the M1. And this is what set the stage for the great 7.62 vs. 5.56 showdown.

Though it is not the iconic weapon of the war, the M-14 was the standard service rifle when Vietnam started. The Air Force was fielding the M-16 in 1962, but everyone else had some good old wood and steel. But the jungle is an entirely different environment. Special Forces, with those abnormal acquisition channels and mustaches, saw the M-16 as solving multiple problems and became early adopters.

The M-16, fully loaded, was two pounds lighter than a loaded M14. Per hundred rounds, 5.56 also weighs around half as much as .308. This matters for a couple of reasons. First, in Special Forces terms, it made sense for our allies. One of the principle jobs of Special Forces in Vietnam was training and fighting with South Vietnamese and Montagnard soldiers. Both of whom, on average, are far smaller in stature than the average American. The Montagnard's, in particular, would be nicknamed "the little people." The M-16 was much easier for them to handle, and became very popular with these brothers in arms.

Second, the same weight per bullet made sense for everyone. While Vietnam has a wide variety of geography, a lot of it is jungle. Fighting in dense jungle vegetation presents unique problems. While I am much too young to have been in Vietnam, I have spent some time in other jungles. And I distinctly remember how claustrophobic it feels when you are new to it. You often can't see ten feet in front of you, which may be the case when a firefight breaks out. Jungle foliage is also notoriously thin, which means bullets zip right through it.

A lot of people are shocked to find out US troops fired around 50,000 bullets per enemy killed during Vietnam. That, in my opinion, is not a reflection on "poor marksmanship" of U.S. forces at the time. Far from it. But it is likely a reflection of how the terrain influences how you fight.

Imagine, for a moment, you are in the middle of a patrol in that same jungle. (Some of you reading this may actually have been. Give us young bucks a minute to catch up.)

You know where your guys are, because you know the direction of march. You can likely see the man in front of you, and the one behind, but that is all. All of a sudden, automatic weapons fire is shredding the jungle around you. Leaves and vines are falling like rain, dirt is kicking up all around you, and you spot the tell-tale muzzle flash of an AK-47 through the veil of green. It isn't steady, but it gives you a vague idea of where the enemy is.

Are you going to carefully line up your irons sights, and wait for a distinct helmet (actually camouflaged perfectly with foliage, and quite possibly dug in) to appear while you slowly squeeze the trigger like you learned on the range? Or are you going to dump a magazine and hope for the best? Me too. I've been in a couple of gunfights where I am absolutely positive I shot at nothing, and I don't regret it a bit.

So while early M-16's had some teething problems with reliability, Vietnam showed the value of having lots of lightweight bullets. The lethality out of a 20-inch barrel was fantastic, and 5.56 would gain popularity around the world as a military caliber.

While some diehards would still never accept 5.56 because it isn't .30 caliber, it did do pretty well in the original design. But when we started chopping the barrel down to 14.5 inches for the M-4, and 10.5 inches for some Special Operations variants, we started running into trouble.

As far back as the Battle of Mogadishu, if you look carefully enough, you can find reports of 5.56 being unreliable in lethality terms from the short barrels. (SFC Randy Shughart, one of the men posthumously awarded the Congressional Medal of Honor from that battle, was notably carrying an M-14.)

5.56 does most of its damage through spalling, kind of a happy accident of design. Above a certain velocity threshold, the bullet positively comes apart in tissue. Even the much maligned "green tip" M855 steel penetrator round shatters into three pieces. This is well known, and backed up by research from giants such as Dr. Martin Fackler, founder and head of the Wound Ballistics Laboratory. But, velocity threshold is the key point here. And 5.56 sheds velocity at every inch of barrel below 20.

Now, as a GWOT era soldier, don't think I am completely negating the 5.56 round. In the last 20 years, ballistics have done a lot for improving the round. While it isn't ideal out of something like a 10-inch barrel, it is still much improved over even the bullets used Oct 3, 1993. Since 9/11, it has put a lot of bad guys in the ground.

And even among troops that have options about what to carry, the debate still rages of 5.56 vs. 7.62. I've used both, and both have merits. But so do a monster truck and Prius. My point isn't that one is better, or both aren't good in certain roles. My point is that both are old, and maybe it is time to evolve.

6.8 as a caliber was first tried at the beginning of the GWOT. A special project between the Army and commercial manufactures yielded the 6.8 SPC round back in 2002. It wasn't quite ready for prime time, but did catch on with the civilian market. Remember the British .280 caliber bullet from way back at the top of this article? 6.8 SPC is remarkably similar.

While we don't know exactly the new bullet parameters the DOD has specified, we do know it has to be 6.8mm. And therefore, 6.8 SPC at least gives us a starting point for understanding. How would, in a hypothetical shoot off, commercial 6.8 SPC fair against 7.62x51 and 5.56x45?

Overall, it would seem to be a pretty good compromise. With barrel, bolt, and magazine changes, it fits in the standard M-4. While it does get crushed at long range compared to 7.62x51, it is also significantly lighter. While it does weigh slightly more than 5.56, it delivers more energy on target at 100-300 meters, and leaves a bigger hole, if we are counting on that.

While on paper, a specialized 5.56 round like Mk262 77 grain will outperform it at longer ranges, that 77 grain bullet is still behind in terms of energy. From shorter barrels designed for CQB, 6.8 SPC will absolutely stomp on 5.56, and at a minimally increased amount of recoil.

So will our troops soon be outfitted with some variant of 6.8 mm rifles? Only time will tell. We spent 12 years and three tests to decide on a new pistol. But at least we are looking. Currently, SIG SAUER, Textron Systems, and General Dynamics are still in the running. Little is known about how things are going, though clues do occasionally pop up.

And some of what we see is borderline science fiction. General Dynamics entry uses a proprietary polymer case design, that would be a huge weight savings. Textron Systems is said to be fielding a cased telescoped round, which wouldn't look out of place in the HALO franchise. And SIG has won so many DOD contracts as of late that only a fool would count them out.

All in all, this is going to be exciting to watch. Weapons evolve, whether we like it or not. If we always settled for good enough, we would still be using musket balls and cannons. Our guys deserve the best option available, whatever the price.