6.8x51 mm

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. It has a very high chamber pressure (maximum average pressure, MAP) of 80,000 psi (550 MPa) in the SAAMI standard. It also means that the.277 Fury is normally chambered in small arms that are capable of handling the accompanying bolt thrust safely. The SAAMI warns that MAP levels greater than 65,000 psi (450 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. On ammunition intended to exceed 65,000 psi (450 MPa), SIG uses a "hybrid" cartridge case design. Each "hybrid" 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 use of higher maximum average pressure (MAP) chamber-pressure levels. The higher MAP enables a 135-grain (8.7 g) projectile to achieve a muzzle velocity of 3,000 feet per second (910 m/s) from a 16-inch (406 mm) barrel, compared to 2,750 feet per second (840 m/s) for a 135-grain projectile in a brass-case reduced-power "practice" load.

SIG's commercial catalogue contains both high-power loads using a hybrid cartridge and reduced-power "practice" loads using a brass cartridge. Commercial types include: 113-grain (7.32 g) hybrid ball (solid copper) described as "Next Gen Ammunition, Magnum Performance", G1 ballistic coefficient (BC) of 0.330. SIG describes this ammunition as the one developed for the US Next Generation Weapon Systems. Only available in 460-round cans or 920-round crates, unlike the others, which are sold as 20-round boxes. 135-grain (8.75 g) brass elite ball described as "Elite Match Grade FMJ Ammunition", G1 BC of 0.475. Reduced-power load classified as "practice". Discontinued 135-grain (8.75 g) hybrid "match grade", G1 BC ≈ 0.488. Same published G1 BC as Sierra.277 135-grain (8.75 g) HPBT MatchKing. Discontinued 140-grain (9.07 g) hybrid "hunter tipped", G1 BC of 0.508. Same published G1 BC as Sierra.277 140-grain (9.07 g) TGK GameKing. 150-grain (9.72 g) hybrid hunter described as "featuring NOSLER Accubond bonded core bullets", G1 BC of 0.500. 155-grain (10.04 g) hybrid match described as "featuring Sierra MatchKing HPBT bullet", G1 BC of 0.549. Do note that ballistic coefficients are somewhat debatable.

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.

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.

XM1168 General Purpose (Prototype) XM1184 Special Purpose. XM1186 General Purpose. Hybrid. XM1188 Reduced Range. Hybrid. XM1192 Blank.