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 Herstal to sustain inventory levels. Navy special operations forces procures their firearms through SOCOM and fielded the MK 16 more than any other unit.

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 their 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 pre-solicitation 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.

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.

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.

Military variants

SCAR-L – 5.56×45mm NATO assault rifle
   * SCAR-L CQC (Close Quarters Combat) – 250 mm (10 in) barrel
   * SCAR-L STD (Standard) – 360 mm (14 in) barrel
   * SCAR-L LB (Long Barrel) – 460 mm (18 in) barrel
SCAR PDW – 5.56×45mm NATO personal defense weapon variant with a 170 mm (6.5 in) barrel length
SCAR-SC- 5.56×45mm NATO subcompact carbine. Weighs 3.1 kg (about 6.8 pounds), has a 7.5-inch barrel, and has a pistol grip with no finger rest. It has a lower effective range of 200m. A 300 blackout version will also be released. Available since mid-2018.
SCAR-H – 7.62×51mm NATO battle rifle
   * SCAR-H CQC (Close Quarters Combat) – 330 mm (13 in) barrel
   * SCAR-H STD (Standard) – 410 mm (16 in) barrel
   * SCAR-H LB (Long Barrel) – 510 mm (20 in) barrel
   FN SCAR Sniper Support Rifle (SSR) – 7.62×51mm NATO semi-automatic sniper system
   Precision Rifles (7.62×51mm NATO)
      * FN SCAR-H PR (Precision Rifle) - 510 mm (20 in) barrel, two-stage match trigger, folding stock, and M16A2 pistol grip.
      * FN SCAR-H TPR (Tactical Precision Rifle) - 510 mm (20 in) barrel, two-stage match trigger, adjustable fixed stock, and M16A2 pistol grip.

Prototypes
   * HAMR (Heat Adaptive Modular Rifle) – Automatic rifle entered in the United States Marine Corps' Infantry Automatic Rifle competition. It was eventually beaten by the M27 Infantry Automatic Rifle, a Heckler & Koch HK416 variant.
   * FNAC (FN Advanced Carbine) – 5.56 mm NATO assault rifle entered into the US Army Individual Carbine competition. The competition was canceled before a winning weapon was chosen.

Civilian variants
   * SCAR 16S – Civilian 5.56×45mm NATO semi-automatic version. Offered in matte black or flat dark earth (brown) color.
   * SCAR 17S – Civilian 7.62×51mm NATO semi-automatic version. Offered in matte black or flat dark earth color.
   * SCAR 20s – Civilian 7.62×51mm NATO semi-automatic version. Offered in matte black or flat dark earth color.