The .277 Fury or 6.8×51mm, (designated as the .277 SIG FURY by the SAAMI) is a centerfire rimless bottlenecked rifle cartridge that was first announced by SIG Sauer in late 2019. It is a hybrid three-piece cartridge and has a steel case head and brass body, which are connected by a locking washer to support its high max chamber pressure of 80,000 psi , which significantly exceeds even rounds with notoriously high pressures.
The cartridge was designed by SIG Sauer for the United States Army’s Next Generation Squad Weapon Program (NGSW). The cartridge was announced for non-military usage along with the SIG Sauer CROSS—a bolt-action, magazine-fed rifle—in December 2019. In 2020, it was accepted by the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) as a new cartridge and chambering. In 2022, SIG Sauer announced that it intends to commercially chamber the SIG MCX SPEAR semi-automatic rifle in .277 Fury.
Ballistic performance of the .277 SIG Fury, using a 16-inch test barrel. Sourced from Tactical Life.
|Bullet Weight & Type||Muzzle Velocity||Energy|
|135 gr (9 g) Hybrid Match||3,000 ft/s (910 m/s)||2,694 ft lbs (3,653 J)|
|140 gr (9 g) Hunter Tip||2,950 ft/s (900 m/s)||2,706 ft lbs (3,669 J)|
According to SIG Sauer, this cartridge has performance that exceeds the highly popular 6.5 Creedmoor. It shows 6 to 9 feet (1.8m to 2.7m) less bullet drop at 1,000 yards (914 meters), while delivering 20–25% greater energy. This is almost certainly a result of the higher chamber pressures that they were able to achieve with the .277 SIG Fury and its hybrid case.
Specifications & More
The cartridge uses a case that is the same length and diameter as the .308 Winchester. Each cartridge case consists of a stainless steel base coupled to a brass body via an aluminum locking washer. Stainless steel has a significantly higher yield strength than brass, which allows the engineers to use higher Maximum Average Pressure (MAP) levels than would be possible with traditional brass casings.
Projectiles (so far), are either 135 grains (8.7 grams) "match grade" with a G1 ballistic coefficient of approximately .488. Or 140 grains (9.1 grams) "hunter tipped" with a G1 ballistic coefficient of about .508.
SAAMI warns in their documentation that Maximum Average Pressure levels greater than 65,000 psi (448.2 MPa) may present increased risk of unsafe cartridge case or firearm rupture and thus require cartridge case and/or firearm designs that depart from traditional practices (materials, construction, and other design criteria).
The .277 FURY SAAMI (voluntary) Maximum Average Pressure (MAP) chamber pressure of 80,000 psi (551.6 MPa) enables a 135 grains (8.7 g) projectile muzzle velocity of 3,000 feet per second (914 m/s) from a 16-inch (406 mm) barrel. It also means that the .277 FURY should only be chambered in small arms that are capable of handling the accompanying bolt thrust safely.
- Case type: Rimless, bottleneck
- Bullet diameter: .2780 in (7.06 mm)
- Neck diameter: .3100 in (7.87 mm)
- Shoulder diameter: .4611 in (11.71 mm)
- Base diameter: .4703 in (11.95 mm)
- Rim diameter: .4720 in (11.99 mm)
- Rim thickness: .0540 in (1.37 mm)
- Case length: 2.015 in (51.2 mm)
- Overall length: 2.825 in (71.8 mm)
- Rifling twist: 1 in 7" (177.8 mm)
- Maximum pressure (SAAMI): 80,000 psi (550 MPa)
Military Contract & Adoption
On April 19th 2022, the United States Army announced that it had selected SIG Sauer to build the new XM5 Rifle to (partly) replace the existing standard M4 carbine, as well as the XM250 Automatic Rifle to replace the already standard M249 SAW. Along with the and that it had selected the company's .277 FURY cartridge, utilizing government provided projectiles and vendor-designed cartridges as ammunition for the new weapon systems. The XM5 and XM250 were designed to fire the 6.8×51mm SIG Fury cartridge based on concerns that improvements in body armor would diminish the effectiveness of the current 5.56×45mm NATO cartridge used in the M4 carbine and M249 SAW. A newer, more effective cartridge would help increase their lethality as well as their effective range when compared to common battlefield rounds such as the 5.56×45mm NATO and 7.62×51mm NATO.
- SIG MCX Spear
- XM5 Assault Rifle
- XM250 Automatic Rifle
- Next Generation Squad Weapon Program
- .277 Wolverine
.277 SIG Fury SAAMI Specs - PDF from SAAMI on cartridge dimensions and other specs for the .277 Fury cartridge.