The SIG MCX is a series of firearms designed and manufactured by SIG Sauer, produced in both selective fire and semi-automatic only configurations, and features a short-stroke gas piston system, which is carried over from the SIG MPX submachine gun.

The SIG MCX with a standard folding stock
TypeAssault rifle
Semi-automatic rifle
Place of originGermany
Service history
In service2015–present
Production history
ManufacturerSIG Sauer
Unit costMCX VIRTUS Patrol: MSRP $2,233 USD
MCX VIRTUS Pistol: MSRP $2,235 USD [1]
VariantsSee Variants
Mass2.61 kg (5.8 lb) (229 mm barrel)
2.72 kg (6.0 lb) (292 mm barrel)
Length730 mm (29 in) stock folded (229 mm barrel)
908 mm (35.7 in) stock unfolded (406 mm barrel)
Barrel length229 mm (9.0 in)
292 mm (11.5 in)[2]
406 mm (16.0 in)

Cartridge5.56×45mm NATO
.300 AAC Blackout
ActionShort-stroke gas-operated piston, rotating bolt
Rate of fire900 RPM
Muzzle velocityMCX Carbine 5.56x45mm NATO: 3,000 ft/s (914 m/s) [3]
Effective firing rangeMCX Carbine 5.56x45mm NATO: 1,650 ft (503 m) [3]
Feed system30-round detachable STANAG box magazine
SightsPicatinny rail for mounting iron or optical sights

The SIG MCX is available in rifle, carbine, short-barreled rifle, and pistol (generally considered as a compact carbine) configurations.[4]


The SIG MCX was first introduced at SHOT Show 2015.


In 2016, SIG recalled some of the rifles that had the first generation bolt carrier group.[5]

Orlando nightclub shooting

A SIG MCX was used in the 2016 Orlando nightclub shooting, which at the time was the deadliest mass shooting in U.S. history, now second to the 2017 Las Vegas shooting.[6]


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.[7] 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.[7][8] The MCX is designed to deliver optimal performance with .300 AAC Blackout and an optional suppressor.[9] 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.[10][11] It features hardened steel wear points.[7][10]

All MCX variants have a forend made of aluminium 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.[7][11]

SIG designed the upper receiver to be compatible with standard AR-15 and M16 lower receivers[7][10] with the help of an adapter.[12] The overall layout of the two rifles is similar.[13]



The SIG MCX is available with a safe/semi-automatic trigger group for the U.S. civilian market, or safe/semi-automatic/fully automatic trigger group for the military and law enforcement agencies.[7]

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).[7]
  • 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,[14] 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.[15] However, as of April 2017, this is no longer the case).[16]

The SIG MCX Low Visibility Assault Weapon (LVAW) is a short-barreled, suppressed, select-fire variant available only available to the military and law enforcement agencies. It is nicknamed as the "Black Mamba".[17][18]


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.[19][20]
  • The SIG MCX VIRTUS SBR is the short-barreled rifle configuration of the MCX VIRTUS. It features a barrel an 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.[3][2]
  • The SIG MCX VIRTUS Pistol is the pistol configuration of the MCX VIRTUS which futures an SBX stabiliser brace. It features a barrel 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.[3][21]


The SIG MCX RATTLER features a 140 mm (5.5 in) barrel and comes either in short-barreled configuration or with a SIG Sauer PCB (pistol pivoting contour folding brace). It is available in 5.56×45mm and .300 AAC Blackout.


CSASS Program

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.[22] 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.[23]


See also


  1. "MCX VIRTUS". Retrieved January 5, 2019.
  2. "Sig MCX VIRTUS SBR". Retrieved January 5, 2019.
  3. "Military Factory - SIG MCX". Retrieved January 5, 2019.
  4. "2017 SIG SAUER Catalog". SIG Sauer. Retrieved 26 February 2017.
  5. "Sig Sauer MCX Mandatory Recall". SOFREP News. 24 December 2014.
  6. Gibbons-Neff, Thomas. "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.
  7. G&A Online Editors (January 13, 2015). "First Look: SIG Sauer MCX". Guns & Ammo.CS1 maint: extra text: authors list (link)
  8. Leghorn, Nick (October 17, 2015). "Gun Review: SIG SAUER MCX". The Truth About Guns. Retrieved June 23, 2016.
  9. "SIG Sauer MCX Carbine". American Rifleman.
  10. Merrill, David (16 January 2015). "RECOIL Exclusive: Breakdown of the Sig MCX". Recoil.
  11. Warden, Drew (October 7, 2015). "Full Review: SIG Sauer MCX". Gun Digest.
  12. "AR Lower Receiver Extension Adapter for SIG MCX Upper - Soldier Systems Daily". Retrieved 2017-06-10.
  13. Utley, Sean (30 June 2015). "Sig Sauer's MCX Rifle: An Elite Modular Weapons System". Tactical Life.
  14. Federal Gun Control Act 1968 18 U.S. Code § 921 - Definitions,, "(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"
  15. "The Rise And Fall Of The SB-15 'Sig Brace'". Grand View Outdoors. 24 March 2015.
  16. "Brace Yourself: ATF Reconsiders Obama-Era Policy on Stabilizing Braces". National Rifle Association Institute for Legislative Action. 25 April 2017.
  17. "On the range with Sig Sauer's MCX 'Black Mamba'". Military Times. 17 April 2014.
  18. Neville, Leigh (31 March 2016). Guns of Special Forces 2001 – 2015. Casemate Publishing. pp. 142–143. ISBN 978-1-4738-8102-0.
  19. Martin, Clay. "Ready for Any Mission: SIG Sauer MCX Virtus — Full Review". Retrieved January 5, 2019.
  20. "Sig MCX VIRTUS Patrol". Retrieved January 5, 2019.
  21. "Sig MCX VIRTUS Pistol". Retrieved January 5, 2019.
  22. Jahner, Kyle (8 April 2016). "H&K confirms: This is the Army's new and improved sniper rifle". Army Times. Retrieved 9 June 2016.
  23. Merrill, David (21 May 2015). "RECOIL Exclusive: An Inside Look at Sig Sauer's CSASS – The MCX-MR". Recoil.
  24. Peter Mitchell (24 July 2017). Elite Force. 7 News Melbourne (Television production). Seven Network. Retrieved 10 November 2018.
  25. Missing or empty |title= (help)
  29. "Indonesia Defence Forum". Pakistan Defence. Retrieved 2017-06-10.
  30. Wilk, Remigiusz (24 November 2016). "SIG MCX rifles delivered to Dutch special forces". IHS Jane's 360. IHS Jane's Defence Weekly.
  31. "U.S. Special Forces to purchase Sig Sauer MCX rifle carbine". Army Recognition. 15 February 2018. Archived from the original on 17 February 2018. Retrieved 17 February 2018.
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