Description
The .277 Fury or 6.8×51mm Common Cartridge, (designated as the .277 SIG Fury by the 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 aluminum locking washer. Stainless steel has a significantly higher yield strength than brass, allowing 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 20–25% greater energy. Reduced-power .277 Fury ammunition, which does not employ the stainless steel case head (.277 Fury Elite ball FMJ), and thus cannot achieve pressure above current SAAMI brass specifications, is virtually identical to the commonly available 7mm-08 Remington, which was developed in 1980.
The bullet diameter of the .277 Fury cartridge is close to that of the 7mm-08 Remington, the difference in diameter is 0.006 inch (0.15 mm) or approximately the thickness of two human hairs. The muzzle velocity and downrange energy of the reduced-power .277 Fury without stainless steel case head and 7mm-08 Remington are practically identical in similarly weighted bullets with similar ballistic coefficients.
Reduced-power .277 Fury ammunition (.277 Fury Elite ball FMJ) performs close to the brass-cased .270/308 Winchester wildcat rifle cartridge, which has a case capacity of 3.5 ml (54 grains) H2O and the bullet, diameter-wise, fills a position between the .260 Remington and 7mm-08 Remington rifle cartridges.
