277 Fury vs. 5.56×45

If the United States Army never updated its rifle ammunition, then it would still be issuing Harpers Ferry Model 1803 rifles. We’re sure the troops would look quite striking while carrying them around, but they’d probably find the four-foot-long flintlock muzzleloaders to be impractical for modern warfare.

Technological advancement and the most aggressive form of competition mankind has ever invented have driven our Army to continually improve its primary combat rifle ammunition over the centuries. Until very recently, its latest and greatest had been the 5.56x45mm. But now that SIG Sauer has been declared the victor (so to speak) of the Army’s Next Generation Squad Weapon, the 5.56 M4 carbine and M249 SAW light machine gun are poised to be replaced by the XM7 and XM250 – both chambered for the novel 277 SIG Fury (aka “6.8x51mm Common Cartridge”).

One might rightly assume that the 277 Fury is better than the 5.56×45 it is designed to supplant. But that begs the questions: In what way? And by how much?

Let’s compare the two rounds and see.

277 Fury vs. 5.56×45: Physical Dimensions

We must preface by stating that this is a true apples-to-oranges comparison.

The 5.56 is a fine intermediate combat cartridge. Despite weighing only 62 grains, the 5.56’s M855 spec FMJ grants the M4 a 500-meter maximum effective range on a point target (i.e. human silhouette). That is effective for close-range engagements, as proven time and time again since the 5.56’s adoption by the Army in the ‘60s.

The 5.56 hasn’t gone without criticism, though. Its ability to neutralize fiercely determined (and heavily drugged) combatants was strongly noted during Operation Gothic Serpent in 1993. Likewise, its ability to penetrate body armor has fallen under increased scrutiny over recent years (which, in fairness, is due in no small part to body armor designers’ best efforts).

The 277 performs much more like the 7.62x51mm (the military analog of the 308 Winchester) than it does any intermediate combat cartridge. Its bullet can easily weigh over twice as much as the 5.56’s, which partially accounts for the XM7 rifle’s 20% farther maximum effective range on a point target.

As you’d rightly surmise, the 277 is a lot more powerful than its predecessor – precisely what it has to be in order to reliably defeat that troublesome, aforementioned modern body armor. As such, it’s reasonable to expect the newer cartridge to be larger.

As you can see, it is in every way. Wider bullet. Broader base. Greater overall length. A case with twice as much capacity for propellant. The 277 has all of these over the 5.56, and it makes very good use of them: by accelerating substantially heavier bullets to similar velocities.

277 Fury vs. 5.56×45: Ballistics

The 5.56 has one ballistic advantage over the 277: its narrower bullet, which equates to less frontal air resistance in flight. That can’t compensate for the 5.56’s chief disadvantage, however: its much lighter weight, which (A) forces it to shed comparably more momentum in flight, (B) makes it more susceptible to the accuracy-weakening effects of wind deflection, and (C) causes it to strike its target with considerably less energy (which we’ll touch on shortly).

These cartridges’ bullets aren’t truly comparable. A 77 grain .22 caliber bullet simply cannot do what a higher-velocity 155 grain 6.8mm one can. The 277 exhibits higher downrange velocity retention in every comparison, and a flatter, easier to aim trajectory as a result. In no uncertain terms, the 277 is the better cartridge for long-distance shooting.

Does that mean the 5.56 is less accurate? Well, that’s not really the right way of looking at things. It is perfectly accurate within the distances it is designed to cover, and we’re willing to bet that a boomer Marine with an M16 would outshoot any zoomer boot with an XM7. Ultimately, accuracy depends more on the shooter’s marksmanship than it does his ammo.

277 Fury vs. 5.56×45: Stopping Power

We must always preface the introduction to “stopping power” by pointing out that the phrase is vague, if not downright undefinable. A bullet’s ability to take down a man or a quarry depends on multiple factors. Some of them (such as the shooter’s marksmanship, which is essential to effective shot placement) are unquantifiable.

But you have to agree that striking energy – i.e. how hard a bullet hits its target – is central to stopping power. That’s why you’d rather get gently smooched on your forehead by a beautiful lady over getting slapped on the same by a sumo wrestler.

To that end, you’d also rather get shot by a 5.56. As detailed earlier, the round’s muzzle energy is less than half that of the 277’s. As you’d expect, the 277 strikes harder at every practical distance as well. To illustrate, consider the distances at which our six comparison rounds conserve at least 1,500, 1,000, and 260 ft lbs of kinetic energy (so chosen because they are the advisable minimum striking power for elk hunting, whitetail hunting, and self-defense, respectively).

There’s no need to belabor this point. The 277 is the heavier-hitter. It’s so much heavier that it can capably deliver more energy to 500 yards than 5.56 ammunition can deliver to one inch from the muzzle.

That all comes with a caveat: you wouldn’t want to use the 277 for home defense. Its heavier recoil, sharper muzzle flip, louder report, and greater likelihood of over-penetration all make it less practical for civilian defense than the 5.56. The newer round may neutralize armored combatants at 600 meters more reliably, but that’s of little benefit to the homeowner while they’re squaring off against a threat in the living room.

277 Fury vs. 5.56×45: Recoil

The 277’s flatter trajectory and superior striking energy come at a cost: more recoil.

Let’s compare our six rounds’ free recoil energy, which is the product of exactly four variables: bullet weight, propellant charge weight, firearm weight, and muzzle veloci</p>

ty. For realism’s sake, let’s assume we are firing a 9.2-pound SIG MCX-SPEAR and a 7.8-pound M16. For simplicity’s sake, let’s assume all 277 cartridges are loaded with 50 grains of propellant, and all 5.56 ones have 25 grains.

Our numbers aren’t set in stone. Different cartridges have different propellant charge weights, and muzzle velocity is never constant. Furthermore, a heavier 277 rifle would generate lower recoil. But those cautions aside, we can safely conclude that the newer round is also the harder-recoiling one. It’s not a shoulder destroyer by any standard, but you’re certain to endure stronger kick while you’re availing yourself of that superior ballistic performance.

277 Fury vs. 5.56×45: Availability and Cost\

At present, the 277 Fury is a niche cartridge. Only one major manufacturer produces it (SIG, of course). No military surplus is available to the commercial market today. If you search, you will find some Sig Sauer 277 Fury Ammo options in-stock.

The 5.56 is the exact opposite. Nearly every major centerfire rifle ammunition manufacturer offers several varieties of it (or, barring that, several varieties of 223 Rem, which any 5.56 rifle can safely fire). The Lake City Army Ammunition Plant, which can produce up to 1.6 billion cartridges each year, pours untold quantities of 5.56 out of its doors.

In short, 5.56 ammo is incomparably easier to buy. It’s a lot cheaper, too, thanks in large part to its smaller size and conventional brass case (the 277 may also be loaded with a solid brass case, though its high-tech three-piece case has a predictable effect on its price tag).

It is quite likely that the 277 will attract increasingly greater demand from the commercial market in years to come – especially as more and more service members become familiar with it, and come to prefer it for deer hunti

ng. When that era comes, the 277 will necessarily go down in price.

But the 5.56 will still cost less to manufacture. It will also have benefitted from a decades-long head start on the market. It will remain in higher demand owing to its more comfortable recoil and better suitability for home defense, too.

The Takeaway

The Army’s newest rifle cartridge trounces the 5.56 in terms of long-range ballistic performance and striking power. It also recoils much harder, and is far more expensive and (for the time being) harder to find.

At the end of the day, the 277 is too different from the 5.56 to ever truly obsolete it. The fact that tens of millions of AR-15s are currently in circulation proves that the older round will stay around for quite some time.

We would only recommend the 277 to firearm enthusiasts who already own multiple rifles, and love laying their hands on the newest and latest thi</p></p>

ng. If you are looking for a proper deer cartridge, then you’ll have an easier time finding decent 308 Win, 30-06 Springfield, 270 Win, and several other suitable types of hun

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ting ammo. But if you’re looking for a range toy that you can also confidently wield during a home defense scenario, then you’ll quickly discover why the 5.56 has become a great friend to countless A

merican shooters.