From Wikipedia -
The Special Forces Combat Assault Rifle, or SCAR, is a modular rifle made by Fabrique Nationale de Herstal (FNH) for the U.S. Special Operations Command (SOCOM) to satisfy the requirements of the SCAR competition. This family of rifles consist of two main types. The SCAR-L, for light, is chambered in the 5.56x45mm NATO cartridge and the SCAR-H, for heavy, fires 7.62x51mm NATO. Both are available in Long Barrel and Close Quarters Combat variants. The FN SCAR system completed low rate initial production testing in June 2007. After some delays, the first rifles began being issued to operational units in April 2009, and a battalion of the US 75th Ranger Regiment was the first large unit deployed into combat with 600 of the rifles in 2009. While purchases of the MK 16 SCAR-L variant by the US Special Operations Command have been canceled, US SOCOM will still buy the MK 17 SCAR-H variant and some subordinate Spec Ops commands are still looking to buy the MK 16 SCAR-L variant and or keep the existing MK 16s they have already purchased.
The SCAR is manufactured in two main versions; Light (SCAR-L, Mk 16 Mod 0) and Heavy (SCAR-H, Mk 17 Mod 0). The L version fires 5.56x45mm NATO using improved STANAG (M16) magazines. The H fires the more powerful 7.62x51mm NATO from a newly designed 20-round magazine. Different length barrels will be available for close quarters battle and for longer-range engagements. The initial solicitation indicated that the SCAR-H would also be chambered for the 7.62x39mm M43 cartridge, and 6.8x43mm Remington SPC cartridge. However, FN is not currently offering other calibers.
The Mk 16 Mod 0 was intended to replace the M4A1, the Mk 18 CQBR and the Mk 12 SPR currently in SOCOM service, before SOCOM decided to cancel the order for the Mk 16 Mod 0 (see below). The Mk 17 Mod 0 will replace the M14 and Mk 11 sniper rifles.
The SCAR features an integral, uninterrupted Picatinny rail on the top of the aluminum receiver, two removable side rails and a bottom one that can mount any MIL-STD-1913 compliant accessories. It has a polymer lower receiver with an M16 compatible pistol grip, flared magazine well, and raised area around magazine and bolt release buttons. The front sight flips down for unobstructed use of optics and accessories. The rifle uses a 'tappet' type of closed gas system much like the M1 Carbine while the bolt carrier otherwise resembles the Stoner 63 or Heckler & Koch G36.
The SCAR is built at the FN Manufacturing LLC, plant in Columbia, South Carolina, United States. Fabrique Nationale introduced a semi-automatic version of the SCAR modular rifle system, the 16S (Light) and 17S (Heavy), at the end of 2008. This version of the SCAR is designed for the law enforcement and commercial markets, and is manufactured in Herstal, Belgium and imported by FNH USA, Fredricksburg, Virginia, United States. FNH USA slightly modifies the rifle (supplying a U.S. made magazine and machining a pin in the magazine well) to be in compliance with U.S. Code before selling them.
In July 2007, the US Army announced a limited competition between the M4 Carbine, FN SCAR, HK416, and the previously-shelved HK XM8. Ten examples of each of the four competitors were involved. During the testing, 60,000 rounds apiece were fired from each of the 40 carbines in an "extreme dust environment." The purpose of the shootoff was for assessing future needs, not to select a replacement for the M4.
During the test, the SCAR suffered 226 stoppages ranking second to the XM8 with 127 stoppages, but less compared to the M4 with 882 stoppages and the HK 416 with 233. This test was based on two previous systems assessments that were conducted using the M4 Carbine and M16 rifle at Aberdeen in 2006 and the summer of 2007 before the third limited competition in the fall of 2007. The 2006 test focused only on the M4 and M16. The Summer 2007 test had only the M4, but increased lubrication. Results from the second test resulted in a total of 307 stoppages for the M4 after lubrication was increased, but did not explain why the M4 suffered 882 stoppages with that same level of lubrication in the third test.
The SCAR was one of the weapons displayed to U.S. Army officials during an invitation-only Industry Day on November 13, 2008. The goal of the Industry Day was to review current carbine technology for any situation prior to writing formal requirements for a future replacement for the M4 Carbine.
On May 4th 2010, a press release on FNH USA's official website announced the SCAR Acquisition Decision Memorandum was finalized on April 14, 2010. This is an approval for the entire weapons family of the Mk16 SCAR Light, Mk17 SCAR Heavy and the Enhanced Grenade Launcher Module.
Introduced in 2004 as an addition, the Enhanced Grenade Launcher Module (EGLM), officially referred to as the FN40GL, or Mk 13 Mod 0, is a 40 mm grenade launcher based on the 'GL1' designed for the F2000. The FN40GL is marketed in both an L and H model, for fitting the appropriate SCAR variant.. The EGLM system features a double action trigger and a swing out chamber. These offer two advantages over the M203 system, the first being that the launcher does not need to be re-cocked if the grenade does not fire, and the latter being that longer grenades can be used.
In 2008, a variant of the FN SCAR was one of four finalist rifles for the Infantry Automatic Rifle (IAR) competition. The IAR is a United States Marine Corps requirement for a lightweight automatic rifle for squad automatic rifle use. The FN entrant is different from existing SCAR versions in that it combines closed bolt operation (fires from bolt forward / chambered cartridge) with open bolt operation (fires from bolt to the rear, no chambered cartridge), switching automatically from closed to open bolt as the weapon's barrel heats up during firing. There have been previous firearms with mixed open/closed bolt operation, but the automatic temperature-based operating mode switch is an innovation. The IAR competition was expected to result in Marine Corps procurement of up to 6,500 automatic rifles over five years, but eventually the SCAR variant was passed over in favor of the Heckler and Koch HK416 rifle, later designated as the M27.