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SAINT
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.
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 require cartridge case and firearm designs that depart from traditional practices (materials, construction, and other design criteria). 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. The cartridge was announced for non-military usage along with the SIG Sauer CROSS—a bolt-action, magazine-fed rifle—in December 2019. As a short-action rifle cartridge (cartridges having an overall length of 2.750 inches 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 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 .277 Fury Demystified
The cartridge uses a case that is the same length and diameter as the .308 Winchester.
Top: .277 SIG Fury. Bottom: .308 WIN.
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 the engineers to use higher maximum average pressure (MAP) chamber pressure levels.
The .277 Fury SAAMI (voluntary) MAP chamber pressure of 80,000 psi enables a 135 grains projectile muzzle velocity of 3,000 feet per second from a 16-inch barrel. It also means that the .277 Fury is normally chambered in small arms that are capable of handling the accompanying bolt thrust safely.
Bullets are either 135 grains "match grade" with a G1 ballistic coefficient of ≈ .488 or 140 grains "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 HPBT MatchKing and .277 140 grains TGK GameKing projectiles.
Commercially, reduced-power .277 Fury Elite ball FMJ ammunition using non-hybrid conventional cartridge cases is offered, that fires a 135 grains projectile with a G1 ballistic coefficient of ≈ .475 at a muzzle velocity of 2,750 feet per second from a 16-inch barrel.
SIG Sauer claims that the cartridge has performance superior to the 6.5mm Creedmoor, exhibiting 6 to 9 feet less bullet drop at 1,000 yards, while delivering 20–25% greater energy.
Top: .277 SIG Fury. Bottom: 6.5 Creedmoor
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 also 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, that 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.
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 XM5 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 weapons' ammunition. The XM5 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 range compared to common battlefield rounds such as the 5.56×45mm NATO and 7.62×51mm NATO.
Operational testing of the XM5 rifle, XM250 automatic rifle, XM157 fire control optic platform agnostic 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.
