How a SCAR-H works

The FN SCAR (Special Operations Forces Combat Assault Rifle) is a gas-operated (short-stroke gas piston) self-loading assault/battle rifle with a rotating bolt. It is constructed to be extremely modular, including barrel change to switch between calibers. The rifle was developed by Belgian manufacturer FN Herstal (FNH) for the United States 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 5.56×45mm NATO cartridge and the SCAR-H, for "heavy", is chambered in 7.62×51mm NATO. Both are available in Close Quarters Combat (CQC), Standard (STD), and Long Barrel (LB) variants.

In early 2004, United States Special Operations Command (USSOCOM) issued a solicitation for a family of Special Operations Forces Combat Assault Rifles, the so-called SCAR, designed around two different calibers but featuring high commonality of parts and identical ergonomics. The FN SCAR system completed low rate initial production testing in June 2007.[11] After some delays, the first rifles began being issued to operational units in April 2009, and a battalion of the U.S. 75th Ranger Regiment was the first large unit deployed into combat with 600 of the rifles in 2009.[2] The U.S. Special Operations Command later cancelled their purchase of the SCAR-L and planned to remove the rifle from their inventory by 2013. However, they will continue to purchase the SCAR-H version, and also plan to purchase 5.56 mm conversion kits for the SCAR-H, allowing it to substitute for the SCAR-L.
The SCAR is manufactured in two main versions; the SCAR-L ("Light") and SCAR-H ("Heavy"). The SCAR-L fires 5.56×45mm NATO, fed from STANAG (M16) magazines. The SCAR-H fires the more powerful 7.62×51mm NATO from proprietary 20-round magazines. Different length barrels are available for close quarters battle and for longer-range engagements. The initial solicitation indicated that the SCAR-H would also be able to be chambered in 7.62×39mm M43 Kalashnikov cartridge and 6.8×43mm Remington SPC cartridge. However, FN is not currently offering them and they likely have been cancelled.

The Mk 16 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 will replace the M14 and Mk 11 sniper rifles. However, the weapon will only supplement other weapons while issuing remains at the operator's decision.

The semi-automatic only Mk 20 Mod 0 Sniper Support Rifle (SSR) is based on the SCAR-H. It includes a longer receiver, a beefed-up barrel extension and barrel profile to reduce whip and improve accuracy, and an enhanced modular trigger that can be configured for single-stage or two-stage operation together with either a folding or a non-folding precision stock.

The SCAR has two receivers: The lower is constructed of polymer, and the upper receiver is one piece and constructed of aluminum.[15] The SCAR features an integral, uninterrupted Picatinny rail on the top of the aluminium receiver, two removable side rails and a bottom one that can mount any MIL-STD-1913 compliant accessories. The lower receiver is designed with an M16 compatible pistol grip, flared magazine well, and raised area around the 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, in the United States. Since 2008, FN Herstal has been offering semi-automatic versions of the SCAR rifles for commercial and law enforcement use. These are dubbed the 16S (Light) and 17S (Heavy), and are manufactured in Herstal, Belgium and imported by FN Herstal's U.S. subsidiary FN America of Fredericksburg, Virginia. FN America slightly modifies the rifles (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.

The FN SCAR 20S Precision Rifle chambered in 7.62×51mm NATO was introduced in 2019. It is a semi-automatic only civilian version of the FN Mk 20 SSR.[18] In 2020 the FN SCAR 20S 6.5CM variant was announced chambered in 6.5mm Creedmoor. This chambering has been selected by USSOCOM for long-range use.
Introduced in 2004 as an addition, the Enhanced Grenade Launching Module[24] (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 (Light) and H (Heavy) 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. Like the M203, the FN40GL uses the same High-Low Propulsion System.

The FN40GL is deemed a third-generation grenade launcher, meaning it is multifunctional: it can be used mounted to the rifle or as a standalone system; it is manufactured using a number of materials like aluminum, composites, and polymers; the breech opens to the side for use of longer 40 mm rounds including less-than-lethal; and it is mounted on the bottom accessory rail instead of requiring specialized mounting hardware. The FN40GL is attached to SCAR rifles on the bottom rail with a trigger adapter and dual locking clamp levers on the launcher, limiting the ability to integrate with other rifles. Barrel length is 240 mm (9.6 in), and is unique in that it is the only system where the barrel can swivel to the left or right for loading, while other breech-loading launchers pivot specifically to one side. This enhances its ambidextrousness, making it easy for a left-handed operator to load under fire. The standalone stock assembly has the FN40GL mounted to the bottom rail as with the rifle, but still has 3 o’clock, 6 o’clock, and 9 o’clock rail positions for other accessories. This is mainly during non-lethal uses for other mounted additions like LED lights and laser dazzlers. The trigger is placed lower than normal for operation with the user's middle finger while keeping their trigger finger free to use the rifle. The double-action trigger is long and heavy to prevent easily and unintentionally firing a round under stress. It can fire the Pike 40 mm guided munition.
In July 2007, the United States 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, 6,000 rounds apiece were fired from each of the carbines in an "extreme dust environment". The purpose of the shoot-off was to assess future needs, not to select a replacement for the M4.

During the test, the SCAR suffered 226 stoppages. Since a percentage of each weapons' stoppages were caused by magazine failures, the FN SCAR, XM8 and HK416 performed statistically similarly. The FN SCAR ranked second to the XM8 with 127 stoppages, but with fewer stoppages compared to the M4 with 882 stoppages and the HK416 with 233. This test was based on two previous systems assessments that were conducted using the M4 carbine and M16 rifle at Aberdeen Proving Ground 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 13 November 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.

The SCAR was one of the competing weapons in the Individual Carbine competition which aimed to find a replacement for the M4 carbine. A variant of the SCAR was entered into the competition, known as the FNAC (FN Advanced Carbine). The weapon is similar to the SCAR Mk 16 Mod 0 but with modifications including a 140 g (0.3 lb) weight reduction resulting in a loaded weight of 3.61 kg (7.95 lb), a bayonet lug for an M9 bayonet (which the Mk 16 does not have), a rail mounted folding front iron sight instead of the gas block mounted sight, and a non-reciprocating charging handle. The competition was cancelled before a winner was chosen.
On 25 June 2010 SOCOM announced that it was canceling the acquisition of the Mk 16, citing limited funds and a lack of enough of a performance difference in comparison to other 5.56mm rifles to justify the purchase. Remaining funds would be expended for the SCAR-H and the Mk 20 sniper variant. At the time, SOCOM had bought 850 Mk 16s and 750 Mk 17s. SOCOM had operators turn in their Mk 16s and is not keeping them in the inventory, but started developing a conversion kit for the Mk 17 to make it capable of firing 5.56mm rounds.

"FN America believes the issue is not whether the SCAR, and specifically the [originally contracted] Mk 16 variant, is the superior weapon system available today...it has already been proven to be just that...recently passing Milestone C and determined to be operationally effective / operationally suitable (OE/OS) for fielding. The issue is whether or not the requirement for a 5.56mm replacement outweighs the numerous other requirements competing for the customers’ limited budget. That is a question that will only be determined by the customer". FN Herstal though had refuted that the Mk 16 was being dropped from the inventory and stated that the 5.56mm variant will be retained by SOCOM, and that "The choice between the 5.56 mm and the 7.62mm caliber will be left to the discretion of each constitutive component of USSOCOM's Joint Command (e.g. SEALs, Rangers, Army Special Forces, MARSOC, AFSOC) depending on their specific missions on today's battlefield".

FN America's claim contradicted the official announcement from SOCOM and they did not reverse their decision. SOCOM decided to procure the 7.62mm Mk 17 rifle, the 40mm Mk 13 grenade launcher, and the 7.62mm Mk 20 Sniper Support Rifle variants of the Special Operations Forces Combat Assault Rifle (SCAR) manufactured by FN. SOCOM would not purchase the 5.56mm Mk 16. At that point the individual service component commands within SOCOM (Army Special Operations Command, Naval Special Warfare Command, Air Force Special Operations Command, and Marine Corps Forces Special Operations Command) would or would not still buy the 5.56mm Mk 16 SCAR for some or all of their respective subordinate units even with overall US Special Operations Command opting not to.

SOCOM began removing the Mk 16 from its inventory at the end of 2011, and most units will have the rifle completely out of their service by the end of 2013. To maintain the SCAR as a small-caliber weapon, they are procuring conversion kits for the Mk 17 battle rifle to make it fire 5.56×45mm rounds. The presolicitation for the SCAR program originally called for one rifle that could be adapted to fire multiple calibers including 5.56mm, 7.62×51mm, and 7.62×39mm. When requirements were finalized, the decision was made to separate the 5.56×45mm and 7.62×51mm weapons because converting the medium caliber rifle to fire small caliber bullets created an assault rifle heavier than the M4 carbine. After fielding, operators reversed the previous decision and called for a SCAR that could change calibers. The Mk 17 was chosen to be scaled down because it had a larger receiver for the 7.62×51mm round, and so the 5.56mm Mk 16 could not be scaled up to chamber the larger round. The 5.56mm conversion kit was finalized in late 2010 and orders began in mid-2011.

On 9 December 2011, the Naval Surface Warfare Center Crane Division released a sole source 5 year indefinite delivery/indefinite quantity procurement notice for the Mk 16 Mod 0 (SCAR-L), Mk 17 Mod 0 (SCAR-H), Mk 20 Mod 0 (SSR), and Mk 13 Mod 0 (40mm EGLM) from FN to sustain inventory levels.] Navy special operations forces procures their firearms through SOCOM and fielded the MK 16 more than any other unit.

The Mk 17 is now in widespread use by United States SOF forces in Afghanistan, where its relative light weight, accuracy and stopping power has proved of worth on the battlefield.