The SIG MCX is a weapon series designed and manufactured by SIG Sauer, featuring a short-stroke gas piston system, carried over from the SIG MPX submachine gun. It is made in both semi-automatic and selective fire configurations. It is available in rifle, short-barreled rifle, and pistol configurations.
SIG MCX rifle with standard folding stock
|Place of origin||United States|
|Used by||Netherlands Maritime Special Operations Forces
U.K. Police CTSFO teams
|Weight||2.61 kg (5.8 lb) (229 mm barrel)
2.72 kg (6.0 lb) (406 mm barrel)
|Length||730 mm (29 in) stock unfolded (229 mm barrel)
908 mm (35.7 in) stock unfolded (406 mm barrel)
|Barrel length||229 mm (9.0 in)
406 mm (16.0 in)
.300 AAC Blackout
|Action||Short-stroke gas-operated piston, rotating bolt|
|Feed system||30-round detachable STANAG box magazine|
|Sights||Picatinny rail for mounting iron or optical sights|
Built at SIG's New Hampshire factory, the MCX was "engineered from the ground up to be silenced, light and short" according to a SIG Sauer brochure.
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.
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-center on installation. The barrel can be changed in a matter of seconds to another length or a different caliber. Additionally the barrels are nitride coated for corrosion resistance. It features hardened steel wear points.
All MCX variants have a forend made of aluminum with a KeyMod system to add accessories. Controls are mostly ambidextrous including the charging handle but not the bolt release. Four types of stocks are available for the MCX carbine.
- MCX Carbine: Carbine, with 16 inches (410 mm) barrel. Available with a safe/semi-automatic trigger group for U.S. civilian sales, or safe/semi-automatic/fully-automatic trigger group for sales to law enforcement agencies and militaries.
- MCX SBR: Short-barreled rifle, with 9 inches (230 mm) barrel. Available with a safe/semi-automatic trigger group for U.S. civilian sales, or safe/semi-automatic/fully-automatic trigger group for law enforcement and military sales. 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.
- MCX Pistol w/ SBX: Semi-automatic pistol, with 9 inches (230 mm) barrel, SIG SBX stabilizing brace and safe/semi-automatic trigger group. This version 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 in general terms, it is 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.
- MCX Low Visibility Assault Weapon (LVAW): Short-barreled, suppressed, select-fire variant available only to law enforcement agencies and militaries. It is nicknamed "Black Mamba".
- MCX-MR (Mid Range): Semi-automatic sniper rifle chambered in 7.62×51mm NATO. It features a 16 inches (410 mm), fluted, 416 stainless steel barrel, with a 1:10 inch twist, manufactured by Bartlein Barrels. The handguard is secured via two screws, and the gas system has settings for suppressed or unsuppressed use. It weighs 8.9 pounds (4.0 kg), and features both an M16/AR-15-type charging handle and a left side charging handle, uses SR-25 box magazines, and is compatible with SR-25 lower receivers. It was SIG Sauer's unsuccessful submission for the United States Army's Compact Semi-Automatic Sniper System (CSASS) program.
- MCX Virtus: In 2017 Sig Sauer announced an update to the MCX line of rifles remaining the series of rifles the MCX Virtus. The MCX Virtus rifles have new upper receivers, handguards, barrels, and bolts which are incompatible with prior MCX versions. 
4 Orlando nightclub shootingEdit
- Wilk, Remigiusz (24 November 2016). "SIG MCX rifles delivered to Dutch special forces". IHS Jane's 360. IHS Jane's Defence Weekly.
- Sculthorpe, Tim (3 August 2016). "ISIS, meet the C-Men: Scotland Yard shows off the first of 600 awesomely armed (and masked) Counter-Terrorism firearms officers who hit the streets today in vans, boats and MOTORBIKES". Daily Mail. Retrieved 24 March 2017.
- Musson, Chris; Gray, Rebecca (28 March 2017). "ARMED ALARMED Scots cops don’t have tools to deal with two neds never mind terrorists as they call for armed officers". The Scottish Sun. Retrieved 28 May 2017.
- "2017 SIG SAUER Catalog". dcatalog.com. SIG Sauer. Retrieved 26 February 2017.
- "Sig Sauer MCX Mandatory Recall". SOFREP News. 24 December 2014.
- G&A Online Editors (January 13, 2015). "First Look: SIG Sauer MCX". Guns & Ammo.
- Leghorn, Nick (October 17, 2015). "Gun Review: SIG SAUER MCX". The Truth About Guns. Retrieved June 23, 2016.
- "SIG Sauer MCX Carbine". American Rifleman.
- Merrill, David (16 January 2015). "RECOIL Exclusive: Breakdown of the Sig MCX". Recoil.
- Warden, Drew (October 7, 2015). "Full Review: SIG Sauer MCX". Gun Digest.
- "AR Lower Receiver Extension Adapter for SIG MCX Upper - Soldier Systems Daily". Retrieved 2017-06-10.
- Utley, Sean (30 June 2015). "Sig Sauer’s MCX Rifle: An Elite Modular Weapons System". Tactical Life.
The MCX has the familiar AR upper and lower receiver layout that we know, but some caveats have been added here. The upper receiver is hardened in select areas, and Sig has developed replaceable parts for those areas that wear the most. One such part is the metal cam-path insert on the side of the upper receiver. Other replaceable parts include a feed ramp insert and the ambidextrous charging handle latch. These items are all steel inserts or pins. The forward assist has an aluminum housing that can be replaced if it wears out. These features reveal that the MCX was meant for long-term use in harsh conditions. In essence, you won’t have to scrap the upper receiver after hard use, only replace some parts. The lower receiver’s controls require no retraining, as they are the same as an AR’s, while the magazine release, bolt release and safety selector are all ambidextrous. Aftermarket drop-in triggers will be right at home, too.
- Federal Gun Control Act 1968 18 U.S. Code § 921 - Definitions, Cornell.edu, "(29) The term “handgun” means— (A) a firearm which has a short stock and is designed to be held and fired by the use of a single hand"
- "The Rise And Fall Of The SB-15 ‘Sig Brace’". Grand View Outdoors. 24 March 2015.
- "Brace Yourself: ATF Reconsiders Obama-Era Policy on Stabilizing Braces". National Rifle Association Institute for Legislative Action. 25 April 2017.
- "On the range with Sig Sauer's MCX 'Black Mamba'". Military Times. 17 April 2014.
- Neville, Leigh (31 March 2016). Guns of Special Forces 2001 – 2015. Casemate Publishing. pp. 142–143. ISBN 978-1-4738-8102-0.
- Merrill, David (21 May 2015). "RECOIL Exclusive: An Inside Look at Sig Sauer’s CSASS – The MCX-MR". Recoil.
- Jahner, Kyle (8 April 2016). "H&K confirms: This is the Army's new and improved sniper rifle". Army Times. Retrieved 9 June 2016.
- "Indonesia Defence Forum". Pakistan Defence. Retrieved 2017-06-10.
- https://www.facebook.com/tgibbonsneff. "The gun the Orlando shooter used was a Sig Sauer MCX, not an AR-15. That doesn’t change much.". Washington Post. Retrieved 2017-07-23.