.277 Fury

The .277 Fury or 6.8×51mm Common Cartridge (designated as the .277 SIG Fury by SAAMI) is a centerfire, rimless, bottlenecked rifle cartridge announced by SIG Sauer in late 2019. Its hybrid, three-piece cartridge case has a steel case-head and brass body connected by an aluminum locking washer to support the high chamber pressure of 80,000 psi (551.6 MPa).
The cartridge was designed by SIG Sauer for the United States Army's Next Generation Squad Weapon Program (NGSW). It is dimensionally similar to the 7.62×51mm NATO service cartridge.
In December 2019, the cartridge was announced for non-military usage, along with the SIG Sauer CROSS bolt-action rifle. As a short-action rifle cartridge (cartridges having an overall length of 2.750 inches (69.85 mm) or less), increased internal ballistic performance for its cartridge-case volume is accomplished by applying high gas-pressure. In 2020, it was accepted by the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) as a new rifle cartridge and chambering. In 2022, SIG Sauer announced that it intends to commercially chamber the SIG MCX Spear semi-automatic rifle in .277 Fury.
The cartridge uses a case that is the same length and diameter as the .308 Winchester. Each "hybrid" cartridge case consists of a stainless steel base coupled to a brass body via an aluminium locking washer. Stainless steel has a significantly higher yield strength than brass, allowing the engineers to use higher maximum average pressure (MAP) chamber-pressure levels. Bullets are either 135 grains (8.75 g) "match grade" with a G1 ballistic coefficient of ≈ .488 or 140 grains (9.07 g) "hunter tipped" with a G1 ballistic coefficient of ≈ .508 (ballistic coefficients are somewhat debatable).
These projectile ballistic coefficients are equal to the publicized specifications of the Sierra .277 135 grains (8.75 g) HPBT MatchKing and .277 140 grains (9.07 g) TGK GameKing projectiles. The SAAMI warns that MAP levels greater than 65,000 psi (448.2 MPa) may present an increased risk of unsafe cartridge-case or firearm rupture and thus will require new cartridge-case and firearm designs that depart from traditional manufacturing practices, including the use of materials, construction methods, production lines, and other important design criteria.
The .277 Fury SAAMI (voluntary) 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 is normally chambered in small arms that are capable of handling the accompanying bolt thrust safely.
Commercially, reduced-power .277 Fury Elite ball FMJ ammunition using non-hybrid, conventional cartridge cases is offered, that fires a 135 grains (8.7 g) projectile with a G1 ballistic coefficient of ≈ .475 at a muzzle velocity of 2,750 feet per second (838 m/s) from a 16-inch (406 mm) barrel.
SIG Sauer claims that the cartridge has performance superior to the 6.5mm Creedmoor, exhibiting 6 to 9 feet (1.8 to 2.7 m) less bullet drop at 1,000 yards (914 m), while delivering 20 to 25 percent greater energy.
In January 2019, the United States military began the Next Generation Squad Weapon Program to find replacements for the M4 carbine and M249 light machine gun. On April 19, 2022, the United States Army announced that it had selected SIG Sauer to build the XM7 rifle to partly replace the M4 carbine, while the XM250 automatic rifle was to replace the M249 SAW in the LMG role. In both cases it had selected the company's Fury ammunition, utilizing government-provided projectiles and vendor-designed cartridges as the new weapon's ammunition.
The XM7 was designed to fire the 6.8×51mm SIG Fury cartridge in response to concerns that improvements in body armor would diminish the effectiveness of the 5.56×45mm NATO round used in the M4 carbine and M249 SAW and increase their lethality and effective ranges compared to common, battlefield rounds such as the 5.56×45mm NATO and 7.62×51mm NATO.
Operational testing of the XM7 rifle, XM250 automatic rifle, XM157 fire-control optic-platform unit, and the 6.8×51mm ammunition squad-weaponry is expected to begin in 2024. However, this does not guarantee actual, widespread future issue. The military designation for this round is 6.8 common cartridge. The XM1186 is the general-purpose 6.8 mm round, with other versions including reduced-range rounds so that weapons chambered in 6.8 mm can fire on existing ranges designed for the 5.56 mm, marking rounds for force-on-force shooting, and blank and tracer rounds.
As of March 2022, the United States Army has a solicitation ongoing for an M240 machine gun 6.8×51mm conversion kit for the 7.62×51mm NATO-chambered M240B and M240L general-purpose machine guns.