277 Fury vs .308 – The Shooter’s Log

Do you want a long-winded introduction that includes:

1. The respective histories of the 277 SIG Fury and 308 Winchester?
2. My personal experiences firing both cartridges?
3. My Aunt Mary’s cheese button recipe?

Then you’re out of luck – and not just because Aunt Mary is so fiercely protective of her intellectual property. You came to this blessed website because you want to know how the 277 Fury performs relative to one of America’s favorite rifle cartridges, and you want that information unfrilled.

I will point out that SIG Sauer didn’t initially intend for the 277 Fury to replace the 7.62x51mm (i.e. the military analog of the 308 Win). It is meant to supercede the 5.56×45 (i.e. the military analog of the 223 Rem.) However, Fury’s performance actually bears far greater resemblance to that of the substantially more powerful 308 Win. (This makes sense in light of the fact that the 277 is designed to penetrate body armor more effectively than 5.56.)

To summarize, comparing 277 to 308 is probably the most practical way to gain a better sense of the former’s performance relative to an already well-known cartridge. Let’s begin by examining the two side by side.

277 Fury vs. 308 Win: Physical Dimensions

Right off the bat, we see that the 277 is a 6.8mm cartridge (hence its other name: “6.8x51mm Common Cartridge”). This puts it in the same league as the 6.8 Remington SPC (which the U.S. Army declined to formally adopt back around 2007). Conversely, the 308 Win is a .30 cal (America’s favorite rifle caliber).

Naturally, its narrower bullet suggests that the 277 should exhibit greater ballistic efficiency (assuming all other variables are equal, or close to it). If two bullets of the same mass attain the same velocity, then the narrower one will encounter less frontal air resistance and conserve greater momentum as a result. (More on that shortly.)

The other glowing difference between the two rounds is their maximum chamber pressures. The 277’s may be as much as 29% higher than the 308’s, which also alludes to superior ballistic performance.

The primary similarity between the two rounds is their case length: 2.015”. (The two rounds’ base diameters are nearly the same as well.) This is not a coincidence, as Sig designed the 277 to function in the same SR-25 pattern magazine as the 7.62×51 (which the U.S. Army likes, because it eliminates the need to purchase innumerable new magazines). Both cartridges share a functionally identical overall length as a result. That primarily means the 277 is a short-action cartridge – just like the 308 – and therefore benefits from the same fast-cycling, lightweight rifle design.

277 Fury vs. 308: Ballistic Performance

Let’s take a deeper look at how one round’s flight compares to the other’s. In the interest of providing the most apples-to-apples comparison, I chose to contrast cartridges with the most similar bullets possible; weight and style. In essence, I’m trying to show how effectively one round moves X grains of lead and copper relative to the other.

That comes with a caveat. The 308 may be loaded with substantially heavier bullets than the 277. Such bullets are characteristically more resistant to wind drift, and conserve higher percentages of their velocity and momentum downrange. In other words, the 308 may offer arguably superior ballistic performance when it is loaded with a bullet that the 277 cannot have.

Velocity

Our first side-by-side (277 130 grain FMJ vs. 308 135 grain JHP) is a little too apples-to-oranges to derive a weighty conclusion from. The other two are far more satisfying, as they contrast bullets that are virtually identical in weight and style.

Those bullets aren’t identical in caliber, of course. And here we see the greatest advantage of the 277’s 10% narrower bullet. Its smaller frontal surface area encounters less air resistance. It generates less drag and enables the bullet to course downrange without shedding as much velocity (hence its higher G1 ballistic coefficients). Because of this, the 277 bullet is able to traverse the distance between points A and B in less time, and exhibit less drop between the same as a result.

Does the 277’s flatter trajectory equate to greater accuracy? Not necessarily. It can certainly help a shooter put their bullet precisely where they intend for it to go. A flatter trajectory allows us to make less accommodation for gravity while they are aiming, and is generally more forgiving of ranging mistakes. That being said, “accuracy” is a product of factors which extend beyond the cartridge itself, such as the shooter’s marksmanship.

Furthermore, the 308’s heavier bullets (which we did not examine, because the 277 doesn’t have comparable analogs) means it has the potential to overcome wind deflection more effectively.

277 Fury vs. 308 Win: Stopping Power

“Stopping power” is similarly difficult to define, largely because it overlooks the necessity of correct shot placement. For illustration, consider a shot to the finger from a 50 BMG versus a shot to the eye from a 25 ACP. While the former cartridge is almost incomparably more powerful, it is far less likely to “stop” the threat under those conditions.

That consideration aside, we can all agree that we largely determine “stopping power” by striking energy (i.e. how hard the bullet hits its target). If you would rather get punched in the chin by Paula Deen than you would by Manny Pacquiao, then you already understand this principle.

To illustrate these cartridges’ potential stopping power, let’s observe the distances at which they retain at least three amounts of kinetic energy: 1,500, 1,000, and 260 ft lbs (chosen because they are recommended as the minimums for elk hunting, deer hunting, and self-defense, respectively).

The 277’s ballistic advantage manifests itself once again. Even when its bullet shares identical weight and nearly identical muzzle velocity, its superior ballistic efficiency enables the 277 to conserve more of its momentum and energy downrange.

In no uncertain terms, the 277 hits harder than the 308 when all other things are as equal as possible. I should point out that the 308’s wider bullet may inflict a more injurious wound, though. I must also note that either cartridge is more than capable of neutralizing a threat over any distance a civilian might reasonably have to defend themself across.

277 Fury vs. 308 Win: Recoil

You probably wouldn’t want to use these rounds for home defense, though. Either one’s bullet is likely to pierce clean through the threat and multiple walls at close range, which can jeopardize innocent bystanders. Either one’s report would be deafening indoors as well. And to cap it all off, both rounds’ strong recoil would make rapid, accurate follow-up shots needlessly difficult.

But is one round’s recoil objectively gentler? Yes – and we can prove it.

We determine free recoil energy by four variables: firearm weight, propellant charge weight, bullet weight, and muzzle velocity. For the sake of comparison, let’s reasonably assume all of our 277 comparison rounds have 50 grains of propellant; all 308 rounds have 40 grains of propellant; and we are firing two 9.2-pound rifles (which, not coincidentally, is the same weight as a SIG MCX-SPEAR 277 rifle).

Here we see the cost of flatter trajectory and higher striking power: greater recoil.

To be sure, the 277’s recoil isn’t jarringly heavier than the 308’s. If we average both sets of comparison rounds, then the 277 has just 3.0 ft lbs more recoil energy – around 23% higher, which ought to prove just barely noticeable.

We are only approximating the two rounds’ relative recoil. In reality, their propellant charges aren’t so uniform. Different styles of rifle can alter the shooter’s perception of recoil too (as can shooting stance, etc.). But at the end of the day, we can reasonably conclude that the 308 has less recoil, and facilitates accurate follow-up shot placement because of it.

277 Fury vs. 308 Win: Availability and Cost

At the time of writing, only one major manufacturer produces 277 Fury ammunition: SIG Sauer itself. It is a niche cartridge, and one that often features a sophisticated case made of three components: steel base, brass body, and aluminum washer.

Conversely, 308 ammo is one of the most popular rifle cartridges in the United States. Almost every major centerfire cartridge manufacturer offers multiple varieties of it. If its case isn’t made of brass, then it is made of even cheaper steel. And unlike 277, military surplus ammunition (primarily interchangeable 7.62×51) is readily available.

All of this is to say that you will pay substantially more for harder-to-find 277 ammo. You’ll encounter the same situation when it comes to rifles. Countless semi-automatics and bolt actions chambered for 308 are available. They are much easier on the wallet than the rare few rifles that are chambered for 277.

The Takeaway

The 308 was introduced to the commercial market in 1952. The 277 made its debut in 2019. It only stands to reason that the similarly sized newer cartridge should encapsulate technology that grants it superior ballistic performance – and that is most certainly the case.

The 277 is by all means the better rifle cartridge: flatter-shooting and harder-hitting, with very little added recoil in exchange. Unfortunately, it is also so novel that factory-loaded ammunition is still somewhat of a rarity, and more expensive as well. Rifles chambered for 277 are relatively uncommon, whereas 308 rifles are ubiquitous.

If you are a shooter who loves the newest and best thing – and have the means to afford it – then you should by all means incorporate the 277 into your arsenal. But if you are a newcomer to the wide world of guns and want ammo that is (A) perfectly serviceable for hunting all American game, (B) far more affordable, and (C) equally available, then you would be much better served by the tried-and-true 308.