The SIG MCX with a standard folding stock
Assault rifle (selective fire variants only)
|Place of origin||United States|
|Unit cost||MCX VIRTUS Patrol: MSRP US$2,233|
MCX VIRTUS SBR: MSRP US$2,233
MCX VIRTUS Pistol: MSRP US$2,235
|Mass||2.61 kg (5.8 lb) (229 mm barrel)|
2.72 kg (6.0 lb) (292 mm barrel)
|Length||730 mm (29 in) stock folded (229 mm barrel)|
908 mm (35.7 in) stock unfolded (406 mm barrel)
|Barrel length||229 mm (9.0 in)|
292 mm (11.5 in)
406 mm (16.0 in)
.300 AAC Blackout
|Action||Short-stroke gas-operated piston, rotating bolt|
|Rate of fire||800 rounds/min|
|Muzzle velocity||MCX Carbine 5.56×45mm NATO: 3,000 ft/s (914 m/s)|
|Effective firing range||MCX Carbine 5.56×45mm NATO: 1,650 ft (503 m)|
|Feed system||30-round detachable STANAG box magazine|
|Sights||Picatinny rail for mounting iron or optical sights|
The SIG MCX is a family of firearms designed and manufactured by SIG Sauer, produced in both selective fire and semi-automatic only models, and features a short-stroke gas piston system, which is inherited from the earlier SIG MPX submachine gun. The MCX is available in rifle, carbine, short-barreled rifle, and pistol configurations (the latter configuration generally conforming to the definition of a compact carbine but for taking a pistol brace rather than a buttstock).
Orlando nightclub shooting
The SIG MCX series features a short-stroke gas piston system to reduce recoil and improve the reliability of the weapon; this was based on the design of the earlier SIG MPX. The MCX features a system that allows for conversion between 5.56×45mm NATO, .300 AAC Blackout, and 7.62×39mm ammunition, using standard 5.56 mm STANAG magazines for 5.56×45mm NATO and .300 AAC Blackout, and specially designed STANAG-compatible magazines for 7.62×39mm. The MCX is designed to deliver optimal performance with .300 AAC Blackout and an optional suppressor. SIG Sauer is yet to deliver the 7.62×39mm configuration and has removed the calibre as an option in their official website.
The barrel's profile is tapered at the crown to allow the installation of muzzle devices and direct-thread sound suppressors without the use of washers that degrade performance and allows the devices to self-centre on installation. The barrel can be changed in a matter of seconds to another length or a different calibre. Additionally the barrels are nitride coated for corrosion resistance. It features hardened steel wear points.
First generation MCX variants have a forend made of aluminium with a KeyMod system to add accessories while second generation MCX variants have an M-LOK handguard. Controls are mostly ambidextrous including the charging handle but not the bolt release. Four types of stocks are available for the MCX carbine.
SIG Sauer offers the rifle in semi-automatic only in three different configurations for the civilian market:
- The SIG MCX being the standard configuration of the rifle with a 406 mm (16 in) barrel.
- The SIG MCX SBR is the short-barreled rifle configuration of the rifle with a 229 mm (9 in) barrel. (Under U.S. federal law, rifles with barrels shorter than 16 inches are Title II weapons, which are subject to federal restrictions, as well as being regulated by state laws).
- The SIG MCX Pistol is the pistol configuration of the rifle with a 229 mm (9 in) barrel or 292 mm (11.5 in) barrel and comes either with the SIG Sauer SBX (pistol stabilising brace) or SIG Sauer PCB (pistol pivoting contour folding brace). (This configuration fits the U.S. legal definition of a "handgun", in that it is only designed to be fired with a single point of contact with the shooter's body, though it is really a compact carbine rifle, as it fires an intermediate round. The BATFE previously warned users that shouldering a weapon fitted with the SIG SBX, or a similar forearm brace, and not registered as a short-barreled rifle, constitutes the making of a short-barreled rifle, which is a Title II weapon. However, as of April 2017, this is no longer the case).
The SIG MCX Low Visibility Assault Weapon (LVAW) is a short-barreled, suppressed, select-fire variant available only to military and law enforcement agencies. It is nicknamed the "Black Mamba".
SIG MCX VIRTUS
The SIG MCX VIRTUS is the second generation of the SIG MCX series and was introduced in 2017.
- The SIG MCX VIRTUS Patrol is the standard configuration that features a 406 mm (16 in) barrel, a 1:7 inch twist, a custom Sig Matchlite Duo Trigger for improved accuracy, a folding and collapsing 5-position stock, four handguard lengths to choose from, interchangeable barrels and a special internal recoil system.
- The SIG MCX VIRTUS SBR is the short-barreled rifle configuration of the MCX VIRTUS. It features a 292 mm (11.5 in) barrel for the 5.56×45mm NATO calibre, and a 140 mm (5.5 in) barrel and 229 mm (9 in) barrel for the .300 AAC Blackout calibre.
- The SIG MCX VIRTUS Pistol is the pistol configuration of the MCX VIRTUS which features an SBX stabiliser brace. It features an 292 mm (11.5 in) barrel for the 5.56×45mm NATO calibre, and a 229 mm (9 in) barrel for the .300 AAC Blackout calibre.
SIG MCX RATTLER
The SIG MCX RATTLER is a short-barreled rifle variant intended to serve as a personal defense weapon, featuring a 140 mm (5.5 in) barrel, and comes with a Picatinny rail tail interface for attaching either a compact buttstock or a folding PCB (pistol contour brace). It is available in 5.56×45mm NATO and .300 AAC Blackout.
The SIG MCX-MR (Mid Range) is SIG Sauer's unsuccessful submission for the United States Army's Compact Semi-Automatic Sniper System (CSASS) program. It is chambered in 7.62×51mm NATO and has selective fire capabilities. It weighs 8.9 lb (4.0 kg) and features a 406 mm (16 in) fluted, 416 stainless steel barrel, with a 1:10 inch twist, which is manufactured by Bartlein Barrels. The gas system features suppressed and unsuppressed settings. Unlike the handguard of the MCX, which slides off after pulling the front pivot pin, the MCX-MR requires popping off two screws first. It features both an M16/AR-15 type charging handle and a left side charging handle. It is uses a 20-round magazine and is also compatible with SR-25 lower receivers for use of SR-25 box magazines.
- Australia: Victoria Police Special Operations Group use the SIG MCX SBR configuration. New South Wales Police Force Tactical Operations Unit use the SIG MCX VIRTUS series including the RATTLER in .300 AAC Blackout.
- Canada: Saskatchewan Conservation Officers.
- Belgium: Belgium Federal Police - Federal Police Special Units.
- Denmark: Danish Armed Forces used by the navy special forces Frogman Corps (Denmark).
- Estonia: K-Commando
- Finland: Used by the Police of Finland.
- France: French Special Forces used by some CPA10 operators.
- Germany: Berlin Police, 300 modified MCXs to meet the police's requirements were ordered in October 2017, plus an additional 160 units for the SEK of Berlin, Landespolizei of Schleswig Holstein, 531 units ordered. Rhineland-Palatinate Police: more than 100 rifles ordered in late 2019. 
- Indonesia: Indonesian National Police Special Response Unit: Gegana Brimob POLRI.
- Italy: Used by the 9th Paratroopers Assault Regiment "Col Moschin", special forces of the Italian Army
- Lithuania: ARAS
- Malta: Used by the Armed Forces of Malta.
- Netherlands: Used by the Netherlands Maritime Special Operations Forces and the Dienst Speciale Interventies. All rifles acquired in .300 AAC Blackout and fitted with the SIG Suppressed Upper Receiver.
- Poland: Jednostka Wojskowa Grom acquired the SIG MCX and MCX RATTLER in .300 AAC Blackout with conversion kits to 5.56×45mm NATO and 7.62×39mm ammunition.
- Portugal: Polícia de Segurança Pública acquired SIG MCX in 5.56×45mm NATO used by Special Operations Group (Portugal).
- Switzerland: Used by the Police cantonale Genève.
- Ukraine: SBU Alpha Group.
- United Kingdom: Used by the Police Counter Terrorist Specialist Firearms Officers including the Metropolitan Police Service of London and UKSF to replace the HK MP5SD3s.
- United States: USSOCOM acquired the RATTLER conversion kit in .300 AAC Blackout.
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