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The SIG MCX with a standard folding stock
Semi-automatic rifle
Assault rifle (selective fire variants only)
Place of originUnited States[1]
Service history
In service2015–present
Production history
ManufacturerSIG Sauer
Unit costMCX VIRTUS Patrol: MSRP US$2,233
MCX VIRTUS Pistol: MSRP US$2,235[2]
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)[3]
406 mm (16.0 in)

Cartridge5.56×45mm NATO
.300 AAC Blackout
ActionShort-stroke gas-operated piston, rotating bolt
Rate of fire800 rounds/min
Muzzle velocityMCX Carbine 5.56×45mm NATO: 3,000 ft/s (914 m/s)[4]
Effective firing rangeMCX Carbine 5.56×45mm NATO: 1,650 ft (503 m)[4]
Feed system30-round detachable STANAG box magazine
SightsPicatinny 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).[5]


The SIG MCX was first introduced at SHOT Show 2015. The rifle was originally designed by SIG USA, the subsidiary of SIG Sauer based in New Hampshire.[1]


In 2016, SIG recalled some of the rifles that had the first-generation bolt carrier group.[6]

Orlando nightclub shooting[edit]

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.[7]


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.[8] 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.[8][9] The MCX is designed to deliver optimal performance with .300 AAC Blackout and an optional suppressor.[10] 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.[11][12] It features hardened steel wear points.[8][11]

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.[8][12]

SIG designed the upper receiver to be compatible with standard AR-15 and M16 lower receivers[8][11] with the help of an adapter.[13] The overall layout of the two rifles is similar.[14]


SIG MCX[edit]

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.[8]

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).[8]
  • 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,[15] 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.[16] However, as of April 2017, this is no longer the case).[17]

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".[18][19]


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.[20][21]
  • 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.[4][3]
  • 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.[4][22]


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.


CSASS Program[edit]

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.[23] 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.[24]


See also[edit]


  1. ^ a b "The Introduction of the MCX Assault Rifle" (PDF). Understanding the Sig Sauer MCX Assault Rifle Used in the Orlando Mass Shooting. Violence Policy Center. June 2016. Retrieved 7 February 2021.
  2. ^ "MCX VIRTUS". Retrieved January 5, 2019.
  3. ^ a b "Sig MCX VIRTUS SBR". Retrieved January 5, 2019.
  4. ^ a b c d "SIG MCX". Military Factory. Retrieved January 5, 2019.
  5. ^ "2017 SIG SAUER Catalog". SIG Sauer. Retrieved 26 February 2017.
  6. ^ "Sig Sauer MCX Mandatory Recall". SOFREP News. 24 December 2014.
  7. ^ 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.
  8. ^ a b c d e f g G&A Online Editors (January 13, 2015). "First Look: SIG Sauer MCX". Guns & Ammo.
  9. ^ Leghorn, Nick (October 17, 2015). "Gun Review: SIG SAUER MCX". The Truth About Guns. Retrieved June 23, 2016.
  10. ^ "SIG Sauer MCX Carbine". American Rifleman.
  11. ^ a b c Merrill, David (16 January 2015). "RECOIL Exclusive: Breakdown of the Sig MCX". Recoil.
  12. ^ a b Warden, Drew (October 7, 2015). "Full Review: SIG Sauer MCX". Gun Digest.
  13. ^ "AR Lower Receiver Extension Adapter for SIG MCX Upper - Soldier Systems Daily". Retrieved 2017-06-10.
  14. ^ Utley, Sean (30 June 2015). "Sig Sauer's MCX Rifle: An Elite Modular Weapons System". Tactical Life.
  15. ^ 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"
  16. ^ "The Rise And Fall Of The SB-15 'Sig Brace'". Grand View Outdoors. 24 March 2015.
  17. ^ "Brace Yourself: ATF Reconsiders Obama-Era Policy on Stabilizing Braces". National Rifle Association Institute for Legislative Action. 25 April 2017.
  18. ^ "On the range with Sig Sauer's MCX 'Black Mamba'". Military Times. 17 April 2014.
  19. ^ Neville, Leigh (31 March 2016). Guns of Special Forces 2001 – 2015. Casemate Publishing. pp. 142–143. ISBN 978-1-4738-8102-0.
  20. ^ Martin, Clay. "Ready for Any Mission: SIG Sauer MCX Virtus — Full Review". Retrieved January 5, 2019.
  21. ^ "Sig MCX VIRTUS Patrol". Retrieved January 5, 2019.
  22. ^ "Sig MCX VIRTUS Pistol". Retrieved January 5, 2019.
  23. ^ Jahner, Kyle (8 April 2016). "H&K confirms: This is the Army's new and improved sniper rifle". Army Times. Retrieved 9 June 2016.
  24. ^ Merrill, David (21 May 2015). "RECOIL Exclusive: An Inside Look at Sig Sauer's CSASS – The MCX-MR". Recoil.
  25. ^ Peter Mitchell (24 July 2017). Elite Force. 7 News Melbourne (Television production). Seven Network. Retrieved 10 November 2018.
  26. ^ "Flashbang - TOU".
  27. ^
  28. ^
  29. ^ "Sask. seals deals to equip conservation officers with carbines".
  30. ^ "FOTOD: Suure politseiõppuse käigus harjutati ohtlike kurjategijate tabamist". June 20, 2018.
  31. ^ "Sturmgewehr soll Terroristen abschrecken - Neue Super-Waffe für Berliner Polizisten".
  32. ^ "STRATEGIE & TECHNIK: Streifengewehr in Schleswig-Holstein: 522 SIG MCX für die Landespolizei". November 25, 2017.
  33. ^ "Polizei in Schleswig-Holstein bekommt 522 neue Sturmgewehre". LN - Lübecker Nachrichten.
  34. ^ "Rheinland-Pfalz stattet Einheit mit Mitteldistanzwaffen aus".
  35. ^ Wilk, Remigiusz (24 November 2016). "SIG MCX rifles delivered to Dutch special forces". IHS Jane's 360. IHS Jane's Defence Weekly.
  36. ^ "Dutch MARSOF officially purchase .300 BLK SIG MCX Rifles". The Firearm Blog. 2016-12-09.
  37. ^ "Request Rejected".
  38. ^ "Спецподразделение "Альфа" и боевые машины: СБУ будет работать в день выборов 2019 – фото и видео". 30 March 2019. Retrieved 28 April 2020.
  39. ^ "SCO19 Spotted With MCX Carbine". Elite UK Forces. 17 November 2015. Retrieved 16 March 2020.
  40. ^ Neville, Leigh (2019). The Elite: The A-Z of Modern Special Operations Forces. Osprey Publishing. ISBN 978-1472824295.p.43
  41. ^ "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.
  42. ^ "MCX Rattler: Sig Sauer's Plan To Make Old SOCOM Rifles Even Deadlier". Task and Purpose. National Interest. 29 October 2019. Retrieved 1 October 2020.

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