.277 SIG Fury Cartridge: Everything You Need to Know

The U.S. Army has been making noise about “Next Generation” weapons and ammunition for years, and it gave firearms manufacturers its design criteria in 2018. The military indicated they wanted a new cartridge for the NGSW program, and it knew the performance that it wanted. The NGSW solicitation specified that the cartridge had to fire its Picatinny Arsenal-designed 135- to 140-grain .277-caliber bullet. We know that this projectile travels more than 3,100 feet per second (fps), but the actual velocity produced by the 6.8x51mm round is currently held secret. The Army intends to make its bullet for this program at Lake City Arsenal, and it placed the burden of cartridge development to figure out how to achieve such a high velocity on the firearms industry. Oh, yes, they also had to design a rifle (NGSW-R) and automatic rifle (NGSW-AR) to fire it.

The Army has never come out and said why it had to be 6.8mm instead of a more commercially popular caliber like the 6.5mm, but there was a classified brief given at the National Defense Industrial Association (NDIA) that offered some explanation. However, those details were not made available for public consumption. The most succinct explanation comes from the Chairman of the Joint Chief of Staff General Mark Milley: “This is a weapon [and cartridge] that could defeat any body armor, any planned body armor that we know of in the future.”

SIG Sauer is the only manufacturer that has pursued and received SAAMI approval for their Next Generation cartridge, and it named the new commercial cartridge the “.277 SIG Fury.” While the commercial variant of SIG Sauer’s cartridge isn’t quite as high-pressure as the military ammunition, it was SAAMI-approved with a maximum-allowable chamber pressure of 80,000 psi. This is a historic moment in ammunition because, until now, the maximum allowable SAAMI-approved pressure was 66,000 psi!

Such a bold move in ammunition development isn’t going to be met with easy acceptance. SIG Sauer unveiled the cartridge in late 2019, but it didn’t receive SAAMI approval until November 2020. The most significant reason for its delay was COVID-19 related. The SAAMI committee had three separate meetings canceled due to travel restrictions; they couldn’t meet to decide whether to approve the cartridge until 2021. The SAAMI committee is comprised of representatives from throughout the firearms industry, so it is their job to self-police the firearm industry and exercise good judgment on behalf of both consumers and manufacturers. When the .277 SIG Fury came up for committee discussion, some members protested at the idea of any cartridge loaded to 80,000 psi. It was uncharted territory for a factory-produced cartridge. The biggest concern was turning something like the .277 SIG Fury loose on a consumer market that was unfamiliar with its capabilities and limitations.

The .277 SIG Fury has a case-head diameter of .470-inch, and a maximum overall length of 2.83 inches. This means it will load and feed from any 7.62x51mm NATO (.308 Winchester) detachable-box magazine. I think it is likely some motivated rifleman will grab the old deer rifle from behind the bedroom door and have it re-barreled for the .277 SIG Fury since that’s all it will take to turn any old .243 Winchester or .308 Winchester into one that fires new hotness. The problem is, while the loaded ammunition is perfectly capable of functioning in that chamber, there’s a very good chance that the rifle will go kaboom if fed a diet of the high-pressure round. I see the potential tragedy unfolding: A guy gets a set of “Go” and “No-Go” gauges for his freshly chambered .277 SIG Fury hunting rifle, one that was never designed for the high pressure. Thinking he’ll gauge the rifle every hundred rounds or so, he thinks he’ll stop shooting when the bolt closes on the “No-Go” gauge. The problem is that there is no guarantee the bolt lugs will slowly “set-back” and give him a warning that they’re about to shear off. Those bolt lugs could go from “fine” to “gone” with one trigger pull. Then, all kinds of hell will break loose. Maybe the bolt blows out the back of the receiver into the shooter’s face, or perhaps the front of the receiver splays open like a banana. Either way, that’ll be one sad and injured — maybe even dead — shooter. No matter how often anyone states their action is “strong enough”, never shoot the .277 SIG Fury in a rifle that wasn’t expressly designed for high-pressure ammunition. At the time of this writing, the only rifle designed for this pressure level is SIG Sauer’s Cross new MCX-SPEAR.;

There are other challenges related to the Fury. They include the difficulty in calibrating currently manufactured gauges at pressures high enough to ensure temperature stability of the powder. Current gauges used by ammunition manufacturers barely function up to 80,000 psi; staying on top of instrumentation will be vital. Also, when pressure gets that high in ammunition, it can spike easily if ammunition is left on the dash of the vehicle, for example, on a sunny day. Temperature stability is nice at lower pressures but vital at 80K.

I’m not all doom-and-gloom. I think the .277 SIG Fury is an exciting cartridge, and I’ve already decided to buy a rifle in one to explore the advantages that the cartridge potentially offers. Advantages? Magnum performance in a standard short-action. All detachable-box magazines designed around the .308 Winchester should accept the .277 SIG Fury. This translates to short-magnum performance from a standard, easy-feeding and compact cartridge.

When the .277 SIG Fury hits retail shelves, two loads will initially be made available: One with Nosler’s 150-grain Accubond LR and SIG Sauer’s 135-grain Open Tip Match (OTM). The G1 ballistic coefficient (BC) for the 150-gr Accubond LR is .591; the 135-grain OTM G1 BC is .488. According to Guns & Ammo’s tests in 2021 at the SIG Sauer Academy, muzzle velocity for these loads out of a 16-inch barrel is around 2,900 feet per second (fps) for the 150-grain load. It’s 3,000 fps for the 135-grainer.

I don’t see too many folks shooting factory ammo in large quantity anytime soon, however, SIG Sauer will eventually make components and load data available so that handloaders can get in on the action. (Yes, SIG Sauer’s hybrid cases for the .277 Fury are reloadable, which can’t be said for other competitors in the NGSW bid for the U.S. Army contract.)

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Will there be additional cartridges planned for a “Fury family?” A representative with SIG Sauer told me, “Yes.” There is no timeline yet, and that person wouldn’t say what was next in line. I’ll step out on a limb and predict that the next one will be a 6.5mm SIG Fury, and I’ll bet that it will be more popular than the .277 SIG Fury proves to be! The .277 SIG Fury arrived to us first because it is simply a commercialization of what SIG Sauer has already been developing for the U.S. Army’s NGSW requirements. The civilian market wants rounds in 6.5mm, 7mm and .30-caliber. That’s why I’d be willing to bet that a 6.5mm SIG Fury is next up. Like the .277, it would push a 140-grain bullet at 2,970 fps from a 16-inch barrel. A 24-inch barrel would send it downrange around 3,100 fps.

Knowing that the SAAMI committee had debated whether to approve the .277 SIG Fury cartridge, they obviously reached an acceptable compromise. Each box of ammunition comes with a large warning printed so that those of us tempted to re-barrel grandad’s deer rifle will know in advance that 80,000 psi will destroy “Old Faithful” in short order. Still, I’m looking forward to the era of high-pressure ammunition and the performance it promises. Rifles will get lighter and more compact as a result, too.