Freshly announced by SIG Sauer Inc. on the US commercial market, the SIG Sauer MCX .277 Fury semi-automatic rifle is the civilian version of the individual weapon developed by SIG Sauer for the NGSW program, aimed at selecting a replacement for the M4 carbine, the M249 SAW light machine gun, the M240 general-purposes machine gun, and the 5.56x45mm and 7.62x51mm NATO rounds for certain close combat units of the US Army.

The SIG Sauer MCX SPEAR is currently one of the two finalists in the NGSW program, and is chambered for a proprietary caliber dubbed .277 Fury – also known in metric as 6.8x51mm – that is built around a proprietary two-piece case: a brass body and a separate stainless steel case held together by a locking washer. The combination is rated to handle 80,000 psi of chamber pressure.

Commercial .277 Fury loads, both with hybrid cases and conventional single-piece brass cases (allowing handloading), are already available on the US market, and the first civilian firearm chambered for .277 Fury – the SIG Sauer CROSS bolt-action precision hunting rifle – was originally announced in late 2019 and launched officially at the 2020 SHOT Show.

One of the main features of the weapons submitted by SIG Sauer to the NGSW program trials – these being, the SPEAR assault rifle and the MG 6.8 light machinegun – is the quick caliber conversion system: both firearms can be converted from their native .277 caliber to 7.62x51mm NATO or 6.5 Creedmoor simply by changing barrel. The civilian-grade SIG Sauer MCX SPEAR semi-automatic rifle retains this capability, offering additional versatility to civilian customers, be them sport shooters, hunters, or law enforcement officers.

The new .277 caliber SIG Sauer MCX SPEAR is a derivative of the SIG Sauer MCX 5.56mm/.300 BLK rifle series, and retains most features of the latter, coming from factory with side-folding, 6-positions adjustable buttstock and a chrome-moly steel 13" barrel with a 1:7" twist rate. The gas piston working system features a two-positions adjustable valve.

The SIG Sauer MCX SPEAR semi-automatic rifle feeds from proprietary 20-rounds translucid polymer magazines. Each MCX SPEAR semi-automatic rifle will come from factory with two boxes of .277 Fury ammunition – respectively a box of 135 gr Elite FMJ rounds with standard brass case and a box of 150 gr Nosler Accubond rounds with hybrid case – as well as with a proprietary .277 SIG Sauer SLX suppressor, manufactured out of Inconel, featuring a high temperature Cerakote finish and a patented Clutch-LOK mounting system for quick and easy installation and removal.